Water temperature wide fluctuation help

[Cutter 54]

I have a small block Ford 363 built new, from Mike Forte with the standard FFR complete kit radiator and hoses. I am assuming the water pump is stock Ford. My question concerns wide variation in engine WATER temperature once the engine is warmed up. According to the water temp gauge, water temp varies from about 190 maximum down to 130 degrees, whether the car is at idle or being driven. This happens while OIL temp stays fairly constant, again according to the Speed Hut gauges. Oil pressure is never a problem. I just had the thermostat replaced with the same result. The water temp sensor is at the intake manifold.

My thoughts center on either air trapped in the coolant (a Google AI suggestion) or more likely the thermostat remains open longer than needed when cooling is triggered. This could cause a see-saw effect and wide swings in coolant temp (but still in normal range) rather than a minimal fluctuation in coolant flow and temperature in the normal situation. Am I missing something?

Again, to repeat, engine oil temperature is very stable and normal. I could not find a discussion of this issue on the forum in a limited search.

Suggestions please?

[rich grsc]

Speed hut has a method of testing to see if the sensor or gauge is bad. Contact them for instructions, could be a bad sensor

[Cutter 54]

OK. I wasn't aware of that.

[CraigS]

If the speedhut test doesn't do you any good please post a pic of your engine so we can see how the rad hoses, T-filler, temp sensor etc are installed.

[steno]

Where is your sensor? Should be on the passenger side, right behind the thermostat opening.

[Cutter 54]

The sensor is screwed into the forward left (driver side) port of the intake manifold. It is left of the distributor and about parallel with the hot water take off for the heater/ defroster, which comes off the water pump housing. Pix to follow.
Some bench testing of the sensor showed an open circuit with no resistance registered by an ohm meter when the sensor was put into boiling hot, room temperature and ice cold water. I don’t trust this result because if the sensor is shot it should give no temp readings at all on the gauge when hooked up to the running motor.
Where am I going wrong here?

One builder recommended using a Tee at the hot water take off for the heater/defroster to connect the water temp sensor.
I THOUGHT the proper location for a water temp sensor is at the point of coolant return to the water pump.
Please educate me.

[BornWestUSA]

What was the outside temperature during your drive? I really don't see a problem here; I only worry about overheating.

I also see large swings; I will try to take note of how cold it gets on the gauge. The guage only gets my attention over 100c, which I seldom see.

[CraigS]

This was my layout on a 351 w/ Performer RPM intake.
222165

[Cutter 54]

Outside temps have been 65-80 degrees F. My concern is the wide range of water temp readings on the gauge. Of course I cannot measure the true temperature of the coolant inside the engine at the point it is being measured to validate the accuracy of the sensor and gauge, which would be ideal. I am asking what the ideal location for the sensor should be on these 351 Windsors, but thanks for responding.

[michael everson]

Pretty sure where you have your sensor there is no water flow.
Mike

[Cutter 54]

OK. Now we are getting somewhere. 3 photos of my setup.
#1: overview showing fan sensor (top arrow) and heater hose takeoff from water pump housing (lower arrow).
#2: Rear intake manifold plugged ports
#3: closer view of fan sensor and heater hose takeoff
Craig, I don’t think I can precisely replicate where you have your temp sensor on my setup. Your thoughts on using a Tee to piggyback the sensor onto the heater hose takeoff??


222202222203

222204

[Cutter 54]

Aha! That can explain everything! Toss me a life jacket.

[CraigS]

The problem w/ a Tee at the heater hose outlet is what happens when the heater is turned off. Some heaters may leave the coolant flow on but I know when I did that (a non standard heater installation) the passenger could feel the radiant heat at their knees. It depends on where the heater core is located.

[michael everson]

Why no just get a thermostat housing with a hole in it for the sensor?
Mike

[rich grsc]

You said you have SpeedHut gauges, but they use 2 wire sensors, you show a single wire?

[Jim Doak]

You said you have SpeedHut gauges, but they use 2 wire sensors, you show a single wire?

The Speedhut sensor for the fan is a single wire. It's grounded through the engine, etc. You just need to make sure not to use thread sealant on the fitting so you get a good electrical connection.

[rich grsc]

He is talking about the water temp gauge and its fluctuation, not the fan

[Cutter 54]

To all the above comments:

-Craig: I realize the coolant (probably) stops flowing through the heater hoses when the heat is off. I a using the optional kit offered with the Roadster complete kit ( Vintage Air basic heater/defrost). This would negate the purpose of a coolant temp sensor. How to work around this? Not sure how to address your question about the heater core location.
The inlet and outflow hoses both go to the heater unit which is mounted at the firewall right behind the dashboard with heater, fan motor and blower in one box.

Mike E: How would I go about doing that? Do I replace the water pump? Outside my wheelhouse....

Rich and Jim: I have decided to eat this big piece of Humble Pie in front of me and admit that the sensor in the picture is the fan thermostat switch sensor with ONE GREEN WIRE. While reviewing the Ron Francis wiring diagrams I realized this is NOT the wire or sensor for the coolant temp. (DOOOHHHH). Feeling pretty dumb at this point. A quick search failed to clarify just where I screwed in the coolant/water sensor. (I know. Senior moment.) I now need to trace wires behind my dash to isolate the DARK BLUE wire connecting the water temp sensor to the water temp gauge. This will take some time and lots of careful loom tubing and elect. tape removal without causing any connection breaks or shorts.

I appreciate the input. Forgive my leaving out some key information, but I still need to resolve what is causing the temp swings. To be continued......

[Cutter 54]

Quick follow up. I found the coolant temp sensor. It is screwed into the upper part of the FFR radiator on the driver side. I believe it is the only fitting on the radiator to accept a sensor. I had simply forgotten I screwed it in there. The wires seem intact, confirmed by getting actual readings on the water temp gauge when the car is running.

I had (falsely) thought there was no port on the radiator for the sensor. Obviously I was wrong. Again, sorry for misleading everyone, including me, in mis-identifying the fan thermostat sensor in the intake manifold.

Now, back to the issue of the temp readings fluctuating......

[rich grsc]

That's is a terrible location for a temp gauge in my opinion. Every time the thermostat opens or closes it will change the temp, it is also where the coolant moves the fastest

[Cutter 54]

I see your point. Let’s speculate on why there IS a port on the radiator for a temp sensor to begin with? A moot issue at this point.
Now, what about using one of the intake manifold ports, like the rear, driver side (plugged) port shown in my photo? See my post from 11/29, post #11, foto #2.I guess I should try it before asking you helpful souls for hand holding. I will do that when I put the dashboard back together.

[Norm B]

Sorry for being blunt but, that position for your engine temp sender is basically useless. If you have a thermostat fail closed your gauge would read cold while your engine severely overheated.
The gauge sender should be in the port in the intake manifold on the driver’s side of the distributor. I believe that you have your fan control sensor/switch in that port now.
If you don’t want the hassle of putting a T in the heater supply port and some kind of flow through system in that line then, get a thermostat housing like the one pictured. Put the fan sensor in the port in the housing.
I ran that way before I “upgraded” to the Sniper system. Used a 180 degree thermostat and a 195 on 185 off fan control sensor. That way the thermostat opened first. If the temp continued to climb the fan would come on and drive the temp down but, shut off before the thermostat closed.
That way the fan stays off while you’re cruising and comes on when you are in stop and go in traffic.

HTH

Norm

[Cutter 54]

Got it Norm. Glad I put the question out. You confirmed what Rich and Mike E said but with the clarification to drive the point through my head, BLUNTLY I might add.

Yes, it does help. Thanks to all. Maybe others will benefit from my groping around in the dark. Happy Holidays. Ed K

[Cutter 54]

Hey Norm, what about using the other intake manifold port on the driver side just aft of the carburetor? This would obviate the need for a Tee, if this is a suitable place to measure engine coolant temp. Thanks.

[Norm B]

That port will be cooler than the front port. Coolant flow in a SBF is primarily front to back through the block and back to front through the heads. The holes in the head gaskets regulate how much coolant flows up into the heads until it reaches the back of the engine. The coolant passages around the exhaust ports are where a lot of heat is picked up and this, combined with the flow design, makes the front of the engine the hottest point at the manifold ports.

A sensor at the back port is much better than what you have now but, not ideal.

Good luck and Happy Holidays

Norm

[Norm B]

When I installed the Sniper system I needed to have two accurate temperature sensor locations. The one for the Sniper is installed in the left port in the intake and I put a Tee in the heater supply line for my temp gauge sensor. The gauge wasn’t accurate unless the heater was on. The coolant wasn’t flowing past the sensor and the gauge read much cooler than the ECT reading on the Sniper display unless the heater was selected on a little. Not good on a hot day when you really want your gauge to be accurate.
They do make flow through heater control units that allow the coolant to circulate when the heater is off but, they were too bulky for my heater hose routing. I made a bypass block out of a piece of 1 inch aluminum plate. There is a 1/4 inch bypass port between the supply and return lines inside the block.
You can just see my temp sensor in the top of the Tee under the distributor shield in the attached picture.
Because your engine is carbureted, you don’t need the second port to be an accurate source of temperature at all times. The water neck port works perfectly fine for a fan control sensor. It will NOT work for your gauge sensor.

Norm

[rich grsc]

Hey Norm, what about using the other intake manifold port on the driver side just aft of the carburetor? This would obviate the need for a Tee, if this is a suitable place to measure engine coolant temp. Thanks.

NO, that is an air intake runner NOT water port

[Norm B]

Sorry, didn’t look at the your pictures closely enough. My manifold has a rear coolant cross over passage with a port into the coolant on each side. I thought yours was the same.
Rich is correct. Your rear manifold ports are into the intake runners and definitely won’t work for coolant temp sensors.
I have got to learn to look more closely.��

Norm

[Cutter 54]

So, Norm, your fabricated bypass block for the heater circulation allows accessing flowing coolant at all times and measures coolant immediately exiting the water pump. Am I right so far? Nice bit of work. Looks OEM. Just as an aside, does that bypass reduce the hot coolant flow to the heater, and diminish its ability to heat/defrost the cockpit? My suspicion is the answer is NO, since a) you would have addressed the issue already and mentioned it by now and b) even if the AMOUNT of coolant going to the heater is reduced due to the bypass, the TEMPERATURE will still be hot as blazes and deliver good heat to the cockpit. Just a thought exercise on my part. Helps to ward off Alzheimers (maybe).

To continue; Now, I could either reproduce what you did, making or buying a bypass device, or install a thermostat housing. I like the latter option. I will now look up available options online but this part and installation are new to me. I don't mean to sound presumptuous asking for more of your generous advice, but please throw me a bone and briefly explain what is involved in the installation. I am willing to try new modifications, but I really don't want to make 2 or 3 or more attempts to get it right. Been there a hundred times with this car.

Thank you Rich for the clarification. Another example of the danger of ASSuming anything. This is all pretty humbling.

Thanks again.

[Cutter 54]

To quote Norm: "get a thermostat housing like the one pictured. Put the fan sensor in the port in the housing."

As I search on Summit Racing, I see a Dorman Thermostat Housing, #902-1003 priced $18.99 offered for a 351 Windsor. It looks identical to your attached photo. Yes?

OK. Drain some coolant, remove hose from water pump, remove therm housing, clean, use ?RTV for new gasket, install new housing, torque, reattach hose, add coolant. DONE.

[Norm B]

Post a picture of your current thermostat housing and we can walk you through what you need to do.
Just for your understanding, the flow for the heater is out of the manifold, through the heat control valve, the heater core and then back to the pump.
I have used the heater a lot and never have the control pulled out more than 1/2 inch. Way too hot beyond that.

The thermostat housing in my picture was from Amazon (just as a disclaimer).

Norm

[Cutter 54]

“I have used the heater a lot and never have the control pulled out more than 1/2 inch. Way too hot beyond that.“

I can imaging using a heater frequently in Nova Scotia. Not so much in Florida where I have the car.

Some engine fotos:(3).

222312222313

I circled what appears to be the housing and arrowed the 2 visible mounting bolts. One large hose and one smaller diameter (bypass) hose seem to complete the items of interest. My photoshopping skills are not the best.

PS. After looking at images online and discussions on Mustang forums I wonder about drilling and tapping out that recess on the top of the housing, just behind the exit hose fitting. I can't help wondering why that recess looks like the perfect spot; seems it was left closed from the casting of the part and sold to some builders or owners who don't need the threaded port for a temp sensor.

[danmas]

“I have used the heater a lot and never have the control pulled out more than 1/2 inch. Way too hot beyond that.“

I can imaging using a heater frequently in Nova Scotia. Not so much in Florida where I have the car.

Some engine fotos:(3).

222312222313

I circled what appears to be the housing and arrowed the 2 visible mounting bolts. One large hose and one smaller diameter (bypass) hose seem to complete the items of interest. My photoshopping skills are not the best.

PS. After looking at images online and discussions on Mustang forums I wonder about drilling and tapping out that recess on the top of the housing, just behind the exit hose fitting. I can't help wondering why that recess looks like the perfect spot; seems it was left closed from the casting of the part and sold to some builders or owners who don't need the threaded port for a temp sensor.


I just pulled my thermostat housing due to a leak. It was about a twenty minute task. I used a suction device to suck out about 1/2 qt of coolant. 5 minutes to put on the new gasket (rtv). I let the gasket sit over night with the bolts finger tight. Then I cranked it down in the morning. Easy. Solid. No drips. That’s in your wheel house. I wouldn’t be creative here. I suppose you could tap the housing and that might work. I dunno…

Best of luck.

Dan

[CraigS]

Yes you could tap that housing but I 'think' the sensor is pipe thread which has a taper to it. When you drill and tap for pipe thread it is real easy to tap a little too far, especially in aluminum. Then your sensor will never tighten up. Sadly this is personal experience typing.

[Cutter 54]

Great advice from both of you. Knowing the pipe thread is tapered is the game changer. Besides, the tap will probably cost more than the housing.
Now to find the exact part, which should be easy…..

Will follow up. Thank you.

[Papa]

Would something like this be a good solution?

https://www.speedwaymotors.com/Mr-Gasket-9713-Chrome-Water-Neck-Gasket-Style-302-351-W-Ford,287934.html?utm_medium=CSEGoogle&utm_source=CSE&utm_campaign=CSEGOOGLE&gad_source=1&gad_campaignid=23033173417&gbraid=0AAAAAD8-Mcm8HjAWcJDV6394QFQOyengE&gclid=Cj0KCQiAubrJBhCbARIsAHIdxD9qmNLFUDfsz4V9w3Zh CYC-kEytR1GfgZ7bJ_kdfY0q9J5VcC1fcR8aAhUHEALw_wcB

[MB750]

“I have used the heater a lot and never have the control pulled out more than 1/2 inch. Way too hot beyond that.“

I can imaging using a heater frequently in Nova Scotia. Not so much in Florida where I have the car.

Some engine fotos:(3).

222312222313

I circled what appears to be the housing and arrowed the 2 visible mounting bolts. One large hose and one smaller diameter (bypass) hose seem to complete the items of interest. My photoshopping skills are not the best.

PS. After looking at images online and discussions on Mustang forums I wonder about drilling and tapping out that recess on the top of the housing, just behind the exit hose fitting. I can't help wondering why that recess looks like the perfect spot; seems it was left closed from the casting of the part and sold to some builders or owners who don't need the threaded port for a temp sensor.

Where you at in FL? If it's in the Tampa area I'd be happy to check things out for a second opinion. Your layout is very similar to mine and my gauge parks around 80C constantly once warmed.

[johnnybgoode]

How tough would it be to swap the two sensors? Use the one in the rad for the fan and the one in the intake for your temp gauge? You could even just temporarily rewire them and see if it fixes the temp swing in you gauge? I have my temp gauge in the manifold and my fan switch in the de-gas (essentially the radiator) tank. Scott

[Cutter 54]

Yes, Papa. I plugged in my engine spec for the "make sure this part fits?" and yes it does. My concerns are it is chrome and will stand out and it is on the more pricey side based on my search. But thanks for the effort. I am not ruling it out at the moment.

[Cutter 54]

To MB 750;

I am in Clermont, which is 1/2 hour west of Orlando. My daughter is in Parrish which is about 90 miles from me. I will keep you in mind. In the past I have also consulted Henry Renaud who is south of you. Helpful, when he has time to breathe!
A brief look at your build says loads about your abilities and mechanical experience. Thanks for the offer.

[Cutter 54]

How tough would it be to swap the two sensors? Use the one in the rad for the fan and the one in the intake for your temp gauge? You could even just temporarily rewire them and see if it fixes the temp swing in you gauge? I have my temp gauge in the manifold and my fan switch in the de-gas (essentially the radiator) tank. Scott

I did consider that but after the comments from Rich (post #20) and Norm B (post #22) I worry my fan switch sensor would be responding to wide swings in coolant temps in the radiator, just what I am seeing with the coolant temp readings on the gauge. I will try it anyway as an experiment.

[Papa]

I did consider that but after the comments from Rich (post #20) and Norm B (post #22) I worry my fan switch sensor would be responding to wide swings in coolant temps in the radiator, just what I am seeing with the coolant temp readings on the gauge. I will try it anyway as an experiment.

Be sure you are clear on what is in each location. The kit-provided fan control is a thermal switch, not a temp sensor/sender like what a gauge or EFI computer needs. The switch simply opens/closes at a certain temperature. These are not interchangeable.


https://youtu.be/wiDxYwwhSik?si=jiuRZHbUNUyP_l83

[rich grsc]

Why make this so hard???? Walk into the local autoparts store ask for a thermostat housing for a 1993 5.0 mustang, with threaded bung.:rolleyes:

[MB750]

To MB 750;

I am in Clermont, which is 1/2 hour west of Orlando. My daughter is in Parrish which is about 90 miles from me. I will keep you in mind. In the past I have also consulted Henry Renaud who is south of you. Helpful, when he has time to breathe!
A brief look at your build says loads about your abilities and mechanical experience. Thanks for the offer.

One thing I can clearly see as different from my setup is that I've got my gauge connector where you've got your fan switch, and my fan switch is installed in my thermostat housing where you've just got a smooth recessed hole. I also don't have a heater core, but none of those ports are in conflict with thermal sensing.

[MB750]

https://thefactoryfiveforum.com/attachment.php?attachmentid=222335&d=1764715577

https://thefactoryfiveforum.com/attachment.php?attachmentid=222336&d=1764715577

[MB750]

I've been thinking about this. The fan switch only needs to know when the coolant temp gets above 80C (or whatever its setpoint is), so putting it on the discharge side of the thermostat but before the radiator is the best location for it. Having it in its current location is overkill from an informational perspective, and if your thermostat fails it'll make the fan run for no reason. Seeing high engine temps with the fan not cycling on is a great tell-tale that your thermostat is not opening.

The engine temp sensor should obviously be in the engine, but BEFORE the thermostat. That way it's showing the actual coolant temp in the engine even if the thermostat isn't open.

I would recommend, as others have, to move the engine temp sensor where your fan switch is currently mounted, and put the fan switch between the outlet of the thermostat and the inlet of the radiator. Since the fan's air flow is only functional if the coolant is flowing, putting it directly in the engine isn't the best place for it IMO.

[rich grsc]

Actually the fan switch could be on the exit from the radiator, then it would only run the fan if the coolant temp didn't fall enough passing through the radiator

[CraigS]

Rich wouldn't that result in a delayed reaction though? In other words the engine gets hot, say from stopping in traffic, but the fan doesn't come on until the water temp after passing through the rad increases.

[rich grsc]

Maybe, what a minute?

[Cutter 54]

Follow up: received the correct thermostat housing from Jegs, aluminum, unfinished with sensor port.(Blue Print Engines #138BPP12310014 Alum therm housing 90 degree angle Ford Small block 302/351W. $18.95 plus $16 shipping).

The gasket is paper so I was planning to spray it with Gorilla Glue contact adhesive on the engine side of the gasket. Request advice on best installation; contact cement, one or both sides of gasket, RTV, or other? One side or both sides of gasket?

I need a reducer to thread the temp sensor onto the housing port which is larger diameter. Then I can button it up, flush the engine with Blue Devil Radiator Flush and fill her up with fresh antifreeze. Final testing will follow.

222868222867.

[Papa]

This stuff works great. Toss the paper gasket and use this instead.

https://a.co/d/4J8BV4N

[gbranham]

Skip the gasket and use RTV. Put it on the neck and manifold, let it sit for a few minutes, install neck with the bolts loose, then torque them the next day.

[Cutter 54]

Thank you both.

[danmas]

Skip the gasket and use RTV. Put it on the neck and manifold, let it sit for a few minutes, install neck with the bolts loose, then torque them the next day.

Follow uncle Greg’s advice. It’s spot on.

[Cutter 54]

Why make this so hard???? Walk into the local autoparts store ask for a thermostat housing for a 1993 5.0 mustang, with threaded bung.:rolleyes:

Quick answer is that the replacement needed to have a 90 degree outflow neck on top to fit my radiator hose, not a 45 degree. Also I prefer an aluminum rather than steel housing, plain finish not chrome. I thought the efficient way to search was online since not all housings are sold by eery vendor; Auto Zone, Advance Auto and O'Reilly's are near by to me. I used Jeg's in the past with great results.

[Cutter 54]

Regarding from MB750, I have 2 points.

1) MB750: "I've been thinking about this. The fan switch only needs to know when the coolant temp gets above 80C (or whatever its setpoint is), so putting it on the discharge side of the thermostat but before the radiator is the best location for it."

That leaves the thermostat housing as an optimum location for the fan switch. Logically that location should be good for the water temp sensor too. That would require a Tee theoretically however, I am not sure the fan switch and temp sensors would both have good exposure to circulating water. Not ideal. It seems the intake manifold, where the fan switch currently is, would be a good alternative for the sensor. My thought is that both locations are exposed to ENGINE coolant whether or not the thermostat is open, closed or fails in the closed position, since coolant will circulate through the engine block, heads and ? intake manifold (I think), as long as the engine is running.

2) MB750: "I would recommend, as others have, to move the engine temp sensor where your fan switch is currently mounted, and put the fan switch between the outlet of the thermostat and the inlet of the radiator. Since the fan's air flow is only functional if the coolant is flowing, putting it directly in the engine isn't the best place for it IMO."

I realize that using the radiator housing for a sensor or fan switch is a mistake and potential liability with a failed thermostat (fan won't go on). For accurate reading on the gauge, placing the temp sensor where the coolant is flowing THROUGH THE ENGINE should be the goal. Please correct me if I'm wrong here, but I think the intake manifold port OR the thermostat housing would be equally good locations for this purpose. As coolant flows through the engine the temps should be the same at either location. This seems to contradict your last sentence above ("Since the fan's air flow is only functional if the coolant is flowing, putting it directly in the engine isn't the best place for it IMO."). What am I missing? As I see it, the fan is useful only when coolant is flowing though the radiator. If the thermostat fails the fan becomes useless. Any cooled coolant in the radiator will not return to the engine. Please comment.

By the way, I DO have a manual "bypass" switch for the fan, incase the fan doesn't trigger, but that seems beside the point.

Getting this resolved is taking so much time since I am sharing one car with my wife, so gathering necessary products and parts has been a challenge. Thank you again for your contributions. I have also been sidelined by properly (re)setting my parking brake cables.

PS. I notice in your second photo there seems to be Teflon tape on the exposed threads of the fan switch sensor. That could compromise the grounding connection and the ability of the sensor to trigger the fan to go on. Just an fyi.