So i have a 03 6.0 f350. 202k miles on her. Since i bought it the coolant temp would never get over 184 no matter how i drove it. Last weekend i did a coolant flush and added rotella elc, installed XDP coolant filter. Replaced upper rad hose and thermostat with brand new one thinking that this was the reason it didnt get up to temp. After taking it on a 2.5 hr drive with highway driving at 70, the truck will still not get up to operating temp. Since the new thermostat install it will hit 188-190 if i get on it, but will quickly jump back down to 186 and stay there. Outside temp of 55 degrees. Any reason why it wont get up to operating temp? I do have a 10-12 degree delta with EOT at about 196-200 and ECT of 186-188.. Will a clogged oil cooler cause coolant not to get up to temp? Any input would be great! Thanks

 

After sitting overnight, check the difference in temp between the oil and coolant sensors, you might have an issue with a sensor.

 

They are usually the same temp or real close if i recall, but i will double check for sure tomorrow. I use a Edge insight cts2 to monitor those things. When truck is warming up, the ECT is usually 10-15 degrees higher than the EOT until the ECT gets to 186 or so then the EOT will pass it. Is this normal?

 

Yep, the EOT lagging 10 or so degrees behind the ECT until around 180-190 is normal.

Besides checking what your temp readings are after the truck has sat for a while there may be another possibility. Ford changed the thermostat housing, I believe around 05, and I’ve seen issues with thermostats not totally sealing on the old housings. If you got a thermostat that included a new housing then that should be a non-issue.

 

Yes i bought a murray thermostat which was all one assembly. I just installed it and bolted it down and installed upper radiator hose. No leaks that i can tell.

 

You will get a cascade of people saying it needs to be a Motorcraft thermostat. I go a step further, it needs to be an International thermostat.

It may or may not fix your issue.

 

I would have got the motorcraft thermostat but they were out of stock and only had the murray thermostat. So i settled with that one. Would a clogged oil cooler cause the coolant not to get up to temp?

 

I’ll second the International thermostat recommendation over Ford or others. I went through 2 Ford thermostats in 6 months. Held 190 for a bit and then soon wouldn’t hold over 180 for both of them. I ended up going with a Mishimoto 200 degree thermostat and it’s been almost 4 years now, still working. I think I have a new International thermostat with housing as a spare somewhere in the garage.

 

Would you happen to have a part number for the international thermostat? Or know where to pick one up?

 

Clogged oil cooler won’t keep coolant from reaching proper temp if the thermostat is working properly.

And honestly thermostats wont necessarily be at the exact temp...a 192 degree stat may open at 190, or 193, or...some depending on quality may be further off.

 

Ill look into getting a new thermostat and try that. Ive read good reviews about the mishimoto thermostats. Might end up getting one of those.

 

Found it in the garage. I got mine either off eBay or Amazon, Arkansas Valley Diesel was the seller.

Part no. is 1839304C92

It was $30, including housing.

 

Awesome thanks alot!

 

Holy cow...looks like their eBay listing is now $102...which is insane! Unless that’s for, like, 4 thermostats!

I definitely like the Mishimoto thermostat. If you get it just make sure you boil it before you install it in the housing. Or get it pre-installed with the cool polished housing

 

Will do! Do you think installing a thermostat that is opening and closing properly will bring my deltas down? Or Will that not affect my deltas.