6CTA m939a2 overheating issue

[dawico]

Yes but what we are saying is don't trust the gage and also you can point it at different areas to determine flow

Yes, I know what you are saying.

I plan on checking the block, hoses, and the radiator with an IR gun and see what is going on.

 

[dawico]

After testing the thermostat, I got to thinking about the design of it. I am curious if the thermostat could get wedged and not open properly. It seems to be an unusual design. The body slides when it opens and I could see some junk causing it to hang closed.

My original thinking is that this is the older design and caused issues so it was changed to the two thermostat design. Below where mine mounts I can see the ports for the two thermostat setup though so I could be wrong.

More or less just thinking out loud here.

On the pic you can see a rust ring from it sitting closed. The ring is around the part of the body that slides when opening.

 

[Csm Davis]

Short answer is yes, I have seen them hang up in both ways.

 

[dawico]

Short answer is yes, I have seen them hang up in both ways.

Is there any known fix for it? I am thinking of hitting it with some fine sandpaper (thermostat housing and ring it rides in) to smooth it up so it can slide a little easier. Replacing it doesn't really seem like a fix for the design issue.

And thank you for the confirmation.

 

[Csm Davis]

Yeah i would make sure it's clean and moves free but no more than one cost I would buy a new thermostat.

 

[dawico]

So a good trip today. I lightly sanded the thermostat and the ring it rides in and put it all back together. Refilled the system with water and drove about 20 miles and hit full highway speed. Temperature gauge rose right to 185° and stayed right there. Fan did not come on at all.

Yesterday's trip was about 5 miles on neighborhood streets with the gauge going up to 240° and the fan running. Might have hit 30mph.

I am going to call it a stuck thermostat and consider it fixed for now.

One more flush and new coolant added and I will go from there.

Thanks again SS for the help and hopefully this thread helps someone else.

 

[Csm Davis]

Only thing is you need to do the 5 mile surface street run again, hwy speeds push enough air that some of these trucks will cool off with no fan, slow steady stop and go will get it hot faster.

 

[74M35A2]

Change the stat. It is old and they don't last forever, it is a consumable maintenance part. My temp was flaky, the stat looked fine, I replaced it anyway, and now my temp behaves exactly like it should. Even holds 180F going 67mph in 10F weather. Warms up faster, all that. Change it, you'll know it is good, and be done with it.

 

[atomoros]

My 923a2 was hitting the 240 range and I would see some coolant, but could not figure where it was coming from. I filled the coolant and all was OK then temp went to 240 range again. I couldn't stop until I reached the top of a hill. Long story short it was the water pump....easy fix!

 

[dawico]

My 923a2 was hitting the 240 range and I would see some coolant, but could not figure where it was coming from. I filled the coolant and all was OK then temp went to 240 range again. I couldn't stop until I reached the top of a hill. Long story short it was the water pump....easy fix!

That was my next plan of attack. They can go out without leaking I hear.

 

[dawico]

Only thing is you need to do the 5 mile surface street run again, hwy speeds push enough air that some of these trucks will cool off with no fan, slow steady stop and go will get it hot faster.

I did that as the first part of my latest test and it stayed cool.

The first day I had heat issues was 35° out and running down the highway.

I am hoping for the best. Tomorrow will include new coolant and another good test run.

 

[Tornadogt]

good news so far.. thanks

 

[dawico]

good news so far.. thanks

Yes sir. I am very happy.

The real test will be this coming week. 100 miles a day all week.

Hopefully I have nothing new to report.

 

[Ford Mechanic]

At what temp did your fan engage?

 

[dawico]

At what temp did your fan engage?

210° if I recall correctly. It kicked on when it should have according to the temperature gauge.

 

[74M35A2]

Mine comes on at 200F, or so the gauge says anyway. Off about 185F. Probably perfect for a 180F stat.