I'm not sure what to look for during the test on this thermostat for the 6.9:

https://www.summitracing.com/parts/mof-rt1049

It's different than any thermostat I've dealt with. Where will I look to see it open? There's several views of it above. I'm about ready to dunk the new one and old one in a pot of water...

 

Answering my own question. Turn the thermostat on its side so you can see the opening valve. At 190 going up it began to open. At 200 it was open at least 1/4". On the cool down it fully closed again at 175 . Repeated the cycle with same results. The old one lost its seal and was open per my guess. Install tomorrow!

 

For the install I posted on the oil burner forum. Some tips for 6.9 thermostat replacers...

https://www.ford-trucks.com/forums/1...l#post20640598

 

Out on a road trip today. My recently installed thermostat seems to be stuck open. It worked perfectly for 1500 miles. Running cold today. I blocked off part of the radiator with some cardboard. Hopefully that will be enough to compensate for an apparently stuck open thermostat.

Was the right part. Came in Motorcraft packaging. I certainly was hoping for more than 1500 miles...

 

If you bought that from Summit, call them, Tell them your not happy and see what they can do.

 

E5TZ-8575-C (Motorcraft RT-1049) .. 192 degree Thermostat ... is what's listed for 1983/89 6.9/7.3 diesel in the 1980/89 Ford Truck Parts Catalog

 

I ended up blocking the entire front of the radiator yesterday and that was not enough to get the temp up much. Was cold out last night, in the high 30's, got the needle off the C and almost to the bottom of the normal range. Limped home on the back roads.

I was wondering if anybody else has seen a new thermostat go open after 1500 good miles? I was driving at highway speed with the temp guage in the middle of the normal range. Then I noticed it start to drop, slowly and surely went right to the bottom of the normal range. It's nice to know I have ample cooling capacity. You have to have a good working thermostat to get up to operating temperature.

Any suggestions on the best source for good thermostats? I've never seen a thermostat go bad so quick before. Usually they are pretty bullet proof...lasting 100's of thousands of miles.

 

I bought it from ford parts giant online. I'm on hold with them now...

 

Waiting to hear how that turned out... because, inquiring minds want to know...

 

hmmm...looking at my testing temps again now that I read the link Karl posted. Seems the thermostat did not close at plus or minus 3 degrees from spec. It needed to cool to 175 to fully close. Maybe it failed the test according to the NAPA link as it was slow to close? Thereby remaining open too far to maintain engine temps. I did install it and it worked great for 1500 miles.

So the closing point is probably at least as important as the opening temp, maybe more important? I'm pretty sure it's open now as it would not build temp.

 

I do have an open RMA return with FPG. It was on Friday so might be Monday till I hear back on the replacement.

 

Yeah, seems like it has failed. Was this a stock 192 thermostat? If so, it's testing 17 F cooler.

 

Ford OEM part number. Motorcraft packaging. Same as Bill posted. I should have returned it but had to put my truck back on the road. Oh well. New one coming. Will test again.

 

FPG could not send a replacement as they are out of stock. Issuing a refund.

Had to reorder from another vendor.

 

I got the replacement thermostat today. I tested it in a pot of hot water along with the one I installed last November. Did three cycles.

Temp up old 185. New 187 opening.

Continued up to 200 where both were open, old opened up a little wider than new.

Temp down, old 176. New 181 closing.

So the new one opens within 3 degrees of spec, which is listed at 190 now, not 192 per the spec number dummy posted. But needs to cool to 181 to fully close. Should I reject the new one? Or install?

Last November when the old one above was new, 5 months and 1500 miles ago, I reported it opened at 190 and closed at 175. These temps might not be as accurate as the ones I took today as I was watching more closely. So 190 open was likely close but not exact. Depending on the angle of observation the actual opening could have been missed by a few degrees.

The new one today opened at hotter temps and in all cases it opened less wide than the old one and closed 4 to 5 degrees sooner on the cool down.

I would have liked to see the open and close at closer to spec, 190, or within plus or minus 3 degrees. That would be within the guidelines that NAPA suggests. That the link Karl posted above in this thread.

so....install or try again?

Recall that the one I installed last November seemed to work perfectly in terms of what I expected to see on the guage and engine performance. A cold diesel is kind of obvious when not operating at temp. The guage showed smack dab in the middle of normal which is normal for my truck.

I pulled the old one as it could not get my truck up to operating temp. Besides the guage not rising I could tell it was cold by the way the engine sounds, the heater was not blowing hot and I could hold the upper hose with no heat there either.