temp running at 160 (did search)

Ok guys and gals, question of the week. I have an 87 4.0 and installed a 195 T-stat b/c engine was not getting much higher than 180. After installng the 195, engine warms to exactly 195 and drops back down to maybe 150 after the t-stat opens. After freeway driving and stop and go through town, the temp doesn't make it past 150/160. My heater isn't blowing very hot either. I burped the system also. Gauge is working properly and I have a new sending unit. What could be the problem for not running any warmer than 180?

Temp is in the 50/60 outside.

All hoses are hot to touch but not boiling too.

is my heater core clogged?

Coolant is clean.

Pressure bottle is about 3/4 full when cool and drops to a 1/4 when t-stat opens.

Maybe a vacuum leak in the coolant system?

Thanks!

Grab the little lever on the heater control valve under the hood and force it one way and the other. Mine got corroded with time and doesn't always open all the way. That doesn't explain the temp reading though. The temp sensor you wanted to replace is the one on the driver's side rear of the head. I say that because there are actually two sensors and lots of people don't know it. If you got the right sensor, try burping the system again. Point the vehicle down a hill and take a 1/2" deep socket and loosen the sensor until antifreeze starts to come out, then tighten it back down. You said you burped the system, but different people have different methods. A bubble at the back of the head right around the sensor is quite common and can be a pain to get rid of .

There are actually two different types of sensors for the gauge as well and will cause different readings. That most likely is not your problem though because you say it rises to about the right temp before dropping back down.

It sounds like you may have gotten too much sealant around the tstat or the new tstat is bad and once it opens it does not close all the way until the temp goes to ambient.

Lots of Luck.

Thanks Tom, I'll give the heater a try. As for the senor, did the right one. I have rebuilt a few 4.2 and 4.0's so they are familiar. I just can't figure out why I am running so cool so I thought I would get some other opinions b/c I need some thinking outside of my personal experience.
Dan

Sounds like your thermostat is sticking open. Even though the thermostat is new, it could still be defective. Good thing it's cheap and fairly easy to replace. I found out after replacing the radiator and all other cooling goodies on my '90 that the "new" thermostat was the culprit all along for my overheating woes. Good luck.

ACE said:

Sounds like your thermostat is sticking open. Even though the thermostat is new, it could still be defective.

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I agree, I had a brand new mopar thermostat that was defective. It opened too late and made my temperature constantly fluxuate between 220 and 190 constantly when driving on the hwy.

Atl XJ said:

I agree, I had a brand new mopar thermostat that was defective. It opened too late and made my temperature constantly fluxuate between 220 and 190 constantly when driving on the hwy.

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Me too, I put in a MOPAR T-stat and it didn't work any better (as I've said before) then the one I took out. Very dissapointing to say the least!
Stant has a made in the USA premium series of T-stats that only costs a few bucks more, fixed my problem.