Engine runs too Cool..

[glastron351]

Hi Guys - I have a MK4 that has an interesting problem...when its cool outside (55-60 degrees approx.) I cannot get my engine temp over 145 when I run on the highway (which I do a lot). When it's really hot out it will come up to about 180-190 then thermostat kicks in and the fan brings the temp down. Thermostat is 170 (I think) but if I cannot get to that temp on the highway I believe it's not even in the picture. In the city and stop and go driving temp's come up and the thermostat cuts in accordingly. Engine is a 408w (stroked 351w block from a 94 F150) with AFR 205 heads and Edelbrock performer RPM aluminum intake. Car does not seem to have any performance issues but I'd hate to have to put a 'winter' front on to block off incoming air flow....
As always looking forward to your thoughts and ideas...

[Norm B]

Three questions:
1) Are you sure your temperature gauge is accurate?
2) Are you running a fail safe thermostat?
3) Did you put teflon tape or some other non conductive sealant around the temperature probe?
Engine temp should at least get to the thermostat opening temperature even on cold days.

A 170 thermostat is too cool and I would switch to a 180 at minimum and would recommend a 190 if you’re using fuel injection.

Norm

[gbranham]

Agree with Norm on the thermostat you have; it's too cold. Also, where is your temp sensor located? Manifold or elsewhere?

Greg

[Jim1855]

Running an oil cooler? Generally, not necessary on a "street" car.
Jim

[gbranham]

Running an oil cooler? Generally, not necessary on a "street" car.
Jim

I think he's talking about coolant temp, not oil temp.

[Jhinkemeyer]

Thermostats don't "cut in" they open gradually starting at the listed temp. I think the cutting in your seeing in the temperatures is just the fan doing its job.

You can usually tell when the t-stat does its thing by keeping a hand on the upper hose as it warms up (at idle in the driveway). Start it cold, the hose should be soft and cool. The hose should stay roughly that way until the thermostat opens, you'll feel it start to build pressure and then "suddenly" start to get much warmer (it should be a noticeable change). If it just warms gradually the whole time the engine is warming up the t-stat may be stuck open.

Since you want to verify/change the t-stat anyways I would just get 180-190 as others mentioned and get in there and swap it out.

[Railroad]

Change the Thermostat, check your ignition base and advance timing.

[Sdonnel]

What kind of radiator are you using? The radiator in my car at, 60 degrees F air temp, cools the temp to 140 at 75 mph. I know the engine is fine, but the low temp is a function of how well it cools at a given speed in my opinion.

[Dgc333]

What kind of radiator are you using? The radiator in my car at, 60 degrees F air temp, cools the temp to 140 at 75 mph. I know the engine is fine, but the low temp is a function of how well it cools at a given speed in my opinion.

That is why you run a thermostat. Regardless of the radiator, no coolant flows through the radiator until the thermostat opens. I would say your thermostat is stuck open and needs to be replaced.

[J R Jones]

I had a thermostat issue in the last week. My recently acquired hi-perf 302 ran 160F which as Norm stated is too cool. I swapped the 160F thermostat out for a (NAPA) Balkamp Safe-T-Stat at 180F.
It ran perfectly 80 miles to Elkhart Lake where I went to parade speed and warmed to 200F. The fan switch terminal end was loose, the fan did not come on.
The trip home temperature was 160F again. I pulled the new thermostat to find a latching device had locked it open. I bought another brand thermostat (non latching) and I am back to 180F.
jim

[Jeff Kleiner]

Sounds like the thermostat is stuck open.

Jeff

[glastron351]

Thanks guys...I will check temps with a temp gun to ensure accuracy and switch to another thermostat. I'm pretty sure I used some liquid sealant on the sending unit. I'll clean that off to remove from the equation....will keep you posted on the outcome.