Oil Temperature problem

[Harley818]

I had a new problem come up lately and wondering if any of the subaru guys have any suggestions......

I've been driving this car in the summer now for 3 years. Super reliable and fun.

Lately, I've noticed that the oil temperature is running around 240 and climbing up to 260 degrees if I push it harder.
I have Prosport gauges. I had a problem with the pressure gauge which turned out to be the sensor.... so I replaced it and pressure is good.
Now I just replaced the Prosport temperature sensor, hoping that would fix the problem, but still have the same temperature gain.
In stop and go traffic, fans come on regularly, at 205/207 degrees coolant temp and cools to 190 quite quickly.
Oil temps running around 240 in stop and go, and higher if I push it.

I am not driving it as often until I find the problem.

Any ideas?
I was thinking of doing an oil change, and taking the filter apart to see if there is anything unusual like metal bits....

thanks.

[Jetfuel]

How about submerging the sensing unit in water to boiling point ( can and a torch) 212*F ...give or take a few *F for elevation. 1*F per 500 feet change from sea level.Just to see accuracy.
A Blackstone oil analysis can determine what metal is present if you find some in the filter

Jet

[Sgt.Gator]

240 is borderline, 260 is bad. Anything above 260 and you are in race engine territory where they plan on rebuilding the engine constantly.
Did you change oil viscosity just before you noticed the temps going up? Going from 5W-30 to 40 or 50 can make temps go up.
If the coolant is not going up that's a partially good sign. Like Jetfuel said, a sensor test in boiling water will tell you if it's the sensor. Usually temp sensors don't fail like oil pressure sensors do though.
Cutting open your oil filter is always educational. Especially if it's full of metal bits . A Blackstone is most helpful if you have a history of them to compare too.

[Bob_n_Cincy]

Hey Harley, I'm thinking your exhaust manifold might be heating up the oil pan.
I got a couple of questions.
1. Are you running a belly pan?
2. Do you have the OEM heat shield on your exhaust manifold?
3. Where is your oil temp sensor located?
4. Are yo sure you don't have air in your coolant system? This causing hot spots in the top of you engine.
Bob

[Harley818]

Thanks Jet.
I'll try the unit in boiling water to see how accurate it is.
I just replaced it and its still indicating the same temps, so I doubt its the sensor but good to know how accurate it is.
Then, I'm replacing the oil tonight, so I'll see whats in the filter if anything, and good idea to do an analysis on it.
Thanks.


How about submerging the sensing unit in water to boiling point ( can and a torch) 212*F ...give or take a few *F for elevation. 1*F per 500 feet change from sea level.Just to see accuracy.
A Blackstone oil analysis can determine what metal is present if you find some in the filter

Jet

[Harley818]

Hi Sgt.
I didn't change the oil viscosity but when I change the oil Im going from 10-30 to 0-30 synthetic. See if that makes any difference.
And tomorrow I'll cut apart the filter to check whats inside.
Thanks, I knew 240 - 260 wasn't good... you confirmed it.


240 is borderline, 260 is bad. Anything above 260 and you are in race engine territory where they plan on rebuilding the engine constantly.
Did you change oil viscosity just before you noticed the temps going up? Going from 5W-30 to 40 or 50 can make temps go up.
If the coolant is not going up that's a partially good sign. Like Jetfuel said, a sensor test in boiling water will tell you if it's the sensor. Usually temp sensors don't fail like oil pressure sensors do though.
Cutting open your oil filter is always educational. Especially if it's full of metal bits . A Blackstone is most helpful if you have a history of them to compare too.

[Harley818]

Hi Bob,

I'm not running a belly pan, and I haven't really changed anything from last year.
I don't have the heat shield but I am using a turbo blanket, ceramic coated the header, and I did wrap the complete exhaust.
Oil temp is taken from a sandwich plate between the oil filter and the block. One thing though, when I switched the pressure switch, I expected a lot of oil to come out of the hole..... but it was just a little dribble. I would have expected a lot of oil, but maybe when the engine is off its all in the pan?
Pretty sure I don't have air in the coolant. I check the level regularly and its always full at the fill tank. I did Waynes mod as well.

thx for the response.


Hey Harley, I'm thinking your exhaust manifold might be heating up the oil pan.
I got a couple of questions.
1. Are you running a belly pan?
2. Do you have the OEM heat shield on your exhaust manifold?
3. Where is your oil temp sensor located?
4. Are yo sure you don't have air in your coolant system? This causing hot spots in the top of you engine.
Bob

[Ajzride]

Seems like a lot of heat in that area that might be inflating the temperature artificially. Maybe you could use something like this to measure temperature at a few places by taping them on temporarily:

https://www.amazon.com/Thermometer-AJY-Bluetooth-Wireless-328Feet/dp/B07YJTRT8W/ref=sr_1_25?crid=1QSIT8AZPDRR2&dchild=1&keywords=bluetooth+temperature+sensor&qid=1594783750&s=lawn-garden&sprefix=Bluetooth+temper%2Clawngarden%2C171&sr=1-25

[lance corsi]

Harley, are you using a stock oil pump or a high volume one? It’s been noted that a high volume pump may cause the oil to overheat as it bypasses.

[Rdone585]

First - I'm not familiar with Subaru engines. I've been around domestic engines all my life. However, one thing you might check is engine vacuum. If you have positive pressure in the engine it may not be flowing as much oil through the motor as needed. If the oil isn't pulled through the engine efficiently it could lead to over heating. If the engine has positive pressure it could be blowing smoke out somewhere, or pushing the dip stick out of the tube. If the engine has a PCV valve, is it working? You can also use an IR temperature meter to see if you have a hot cylinder. I've seen oil temps of 250 on the track but that's pushing it hard for 20 min sessions at 6K+ RPMs. I've since added an oil cooler and even pushing it the temps stay about 220. Since your coolant temperature is under control and the oil is hot, there likely is friction somewhere causing the extra heat in the oil. The contents of the filter might shed a lot of light on what may be going on. If not, you might consider a compression or a leak down test.

[Harley818]

Harley, are you using a stock oil pump or a high volume one? It’s been noted that a high volume pump may cause the oil to overheat as it bypasses.

I'm using the stock oil pump. Worked well for the last 3 summers.

[Harley818]

I have two catch cans on the venting side. Not catching any oil though.
But you've given me a couple more things to think about.



First - I'm not familiar with Subaru engines. I've been around domestic engines all my life. However, one thing you might check is engine vacuum. If you have positive pressure in the engine it may not be flowing as much oil through the motor as needed. If the oil isn't pulled through the engine efficiently it could lead to over heating. If the engine has positive pressure it could be blowing smoke out somewhere, or pushing the dip stick out of the tube. If the engine has a PCV valve, is it working? You can also use an IR temperature meter to see if you have a hot cylinder. I've seen oil temps of 250 on the track but that's pushing it hard for 20 min sessions at 6K+ RPMs. I've since added an oil cooler and even pushing it the temps stay about 220. Since your coolant temperature is under control and the oil is hot, there likely is friction somewhere causing the extra heat in the oil. The contents of the filter might shed a lot of light on what may be going on. If not, you might consider a compression or a leak down test.

[Harley818]

Hi Bob,
You might be on the right track here.
It does seem like the engine is running hotter lately.

I'm not losing any coolant, but I'm wondering if the heater bypass line might be pinched a little.
First two years I ran with a small hose connecting the two heater lines on the engine.
Last year I hooked up the heater with a bypass so the coolant could continue flowing even if I didn't use the heater.
I thought it was running a little hot a few weeks ago, so I disconnected the heater and went back to the dedicated bypass hose (connects the two lines directly at the engine).

Tomorrow I'll get a new chunk of hose and hook it up so it isn't pinched or restricted. It seems hot to touch so I don't think that is the problem but who knows?

What else could be causing a hot spot?
Since the engine isn't overheating, wouldn't that mean the coolant bubble would be pushed through?
When I shut down the engine, I can hear the coolant percolating through the turbo area. Its definitely hot.

[Bob_n_Cincy]

Hi Bob,
You might be on the right track here.
It does seem like the engine is running hotter lately.

I'm not losing any coolant, but I'm wondering if the heater bypass line might be pinched a little.
First two years I ran with a small hose connecting the two heater lines on the engine.
Last year I hooked up the heater with a bypass so the coolant could continue flowing even if I didn't use the heater.
I thought it was running a little hot a few weeks ago, so I disconnected the heater and went back to the dedicated bypass hose (connects the two lines directly at the engine).

Tomorrow I'll get a new chunk of hose and hook it up so it isn't pinched or restricted. It seems hot to touch so I don't think that is the problem but who knows?

What else could be causing a hot spot?
Since the engine isn't overheating, wouldn't that mean the coolant bubble would be pushed through?
When I shut down the engine, I can hear the coolant percolating through the turbo area. Its definitely hot.

On the 818 wayne's mod should take any air in top of the engine to the degas tank. The problem I was seeing is that air would also form in the top of the radiator. That's why i added the bleed hose from the top of the radiator to the degas tank. I don't know enough about the heater loop to make a recommendation. If you have air pockets in the heater loop, it will prevent hot water getting to the back of the thermostat and preventing it from working properly.
Bob

[Harley818]

Thanks Bob,
Whenever I check the front radiator, its full to the top, however I haven't checked for a while so I'll check today.
I do have Wayne's mod, so the engine should be good. When I disconnected the heater hose yesterday, it didn't seem full....
I'm going to replace the hose today, so I'll check that again as well.


Harley


On the 818 wayne's mod should take any air in top of the engine to the degas tank. The problem I was seeing is that air would also form in the top of the radiator. That's why i added the bleed hose from the top of the radiator to the degas tank. I don't know enough about the heater loop to make a recommendation. If you have air pockets in the heater loop, it will prevent hot water getting to the back of the thermostat and preventing it from working properly.
Bob

[Harley818]

Update:

Front radiator is full right to the cap.
Expansion tank on top of the engine is full right to the cap. I have done Wayne's mod, so hopefully engine is full of coolant. Its been good for the last 3 years.
Pulled the oil filter apart, and good news is there is absolutely nothing in it except oil. So the engine isn't destroying itself inside.
I replaced the heater hose bypass from the metal pipe coming up from the water pump to the other metal pipe going back on top of the engine. There were a couple fitting connectors, so now just heater hose. This would eliminate any possible restriction from a connector.
This morning I'll boil some water and check the accuracy of the oil temp gauge. I replaced the sensor a few days ago and am still reading high temps of 260F.
Then I'll test drive again to see if the heater hose replacement makes any difference.

Last year I had some misfire and backfire due to loose crank pulled and car going into limp mode. I'm wondering if the timing belt could have jumped? Car runs smoothly with lots of power, so I have not checked this yet, but maybe its off enough to generate more heat due to timing being off??

I'll post updates tomorrow with what I find. Any suggestions welcome.

[Harley818]

OK tested the gauge and sensor.
Boiled a pan of water on the stove..... ran to the garage and immersed the sensor..... read the gauge in the dash.
Gauge reads 238F with water slightly less than boiling so 210F?
Looks like the gauge is the problem. Thanks ProSport.... gauge is only 3-4 yrs old with little usage compared to a daily driver.
I'm normally running around 240F and 260F on the gauge when its really hot..... so I'm guessing thats close to really being around 220F
I'll go looking for an Autometer or other gauge.

Thanks for you help and suggestions.....

[STiPWRD]

I've got the same ProSport oil temp gauge. One other thing you may want to check is if the sensor is bad rather than the gauge. It's a thermistor type sensor so you can read the resistance value with a multimeter instead of the gauge and compare it to its datasheet values. It's also good to have a calibrated sensor to put in the boiling water to verify the assumed 212F. I've done this sort of thing before and the temperature can really jump around in boiling water. Ice water is much more stable but the sensor may not be accurate in that lower temp range.

[Jetfuel]

If you have a data sheet that gives you the value resistance vs indication that’s the ticket since you can use a decade box, dial a resistance value and check the reading for such resistance
I read somewhere in the Prosport web page ( when you first stated your issue) that their values for their sending unit was something like 60-930 ohms for 36-320. *F....
If you can find out from Prosport what a fixed resistor ( I’ll do 100 ohms) will equate in *F readings then you should be golden cause you can see if it is the sender or the gauge

Jet....

[Hindsight]

I saw 250+ on the track with mine, and that was with a Setrab air-oil dedicated oil cooler and massive AN fittings and lines, and a SPAL fan on it. I could not find a great place for it to get a blast of airflow though, which would have been much better than a fan. People who have put things behind the side scoops (intercoolers, etc) have not had much luck with that because while the area in front of the scoops is high pressure, the engine compartment is even higher pressure so you don't get flow. I also saw high coolant temps too though, but in my case that was caused by running the OEM radiator and not having good ducting. The kit radiator ducting doesn't really work well and if you do things like a custom front hinge (IE from ZeroDB), you'll need to fab up your own solution and that's kind of a pain in the rear. IMHO the only way to get an oil cooler to work right is to do it like Porsche does their 911 turbo intercoolers. You have a sealed duct running to the intercooler on one side, and another sealed duct running to cut-outs in the rear bumper where there is a low-pressure zone. The only issue is that I don't know if that area of the bumper actually IS a low pressure zone on the 818. You would have to test it first.

[Bob_n_Cincy]

I saw 250+ on the track with mine, and that was with a Setrab air-oil dedicated oil cooler and massive AN fittings and lines, and a SPAL fan on it. I could not find a great place for it to get a blast of airflow though, which would have been much better than a fan. People who have put things behind the side scoops (intercoolers, etc) have not had much luck with that because while the area in front of the scoops is high pressure, the engine compartment is even higher pressure so you don't get flow. I also saw high coolant temps too though, but in my case that was caused by running the OEM radiator and not having good ducting. The kit radiator ducting doesn't really work well and if you do things like a custom front hinge (IE from ZeroDB), you'll need to fab up your own solution and that's kind of a pain in the rear. IMHO the only way to get an oil cooler to work right is to do it like Porsche does their 911 turbo intercoolers. You have a sealed duct running to the intercooler on one side, and another sealed duct running to cut-outs in the rear bumper where there is a low-pressure zone. The only issue is that I don't know if that area of the bumper actually IS a low pressure zone on the 818. You would have to test it first.

Hindsight. I posted a slow-motion video of the rear of the car in a wind tunnel. This can give you a clue whats going on.


https://www.youtube.com/watch?v=I7XDxiXPtak

Bob

[Harley818]

Installed my new AutoMeter oil temp gauge today.
Went for a spin.....
Prosport gauge is reading 260 - 280 when I push it.
Autometer gauge ranges from 205 - max of 210F.

Looks like I will be replacing the rest of my gauges given this is the second Prosport gauge or sensor thats failed now.
What a waste of time..... but better to be safe than sorry.

Thanks for your help guys.

[Mitch Wright]

I was just going to say check the sender or the gauge, I had a bad sender for my AIM MXL. Replacing it fixed it. Glad to hear the gauge was the issue.

[Blwalker105]

You might consider Speedhut.com. Fully customizable, American-made stuff. Also, reasonably priced.