Its pretty possible there is air trapped somewhere. I think this happened to me recently. My car would get to 100 or slightly higher a lot even if it was cold. A dew weeks ago I went to dallas in it and it would run about 95-100 the whole way. Well just a couple days ago I went to check the oil and the car was completely cold and had rock hard radiator hoses. It scared the crap out of me and I loosened the radiator cap and a lot of air escaped. Thinking I had a blown head gasket I read every thread I could and I decided to monitor it. Well it seems my car now runs about 85 now most of the time with an occasional spike to 90 or a little higher. I can only assume there was air trapped in there and it finally made its way out somehow.

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1984 300SD Orient Red/ Palomino
1989 560SEC
2016 Mazda 6 6 speed manual
1995 Ford F-150 reg cab 4.9 5speed manual

Thanks, but in my last post I stated that I have tested this one and it's barely opening at 100 degrees C...

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Jake, 15 years working on Toyota's for a living, self employed now- Landcruiser restorations.
1985 W123 300D CA emissions, 225K miles; deleted cat/oxidizer, all EGR removed
1997 Supercharged 4runner desert buggy
1993 Cummins D250 ~250hp 650 ft lbs, keeping it mild
1978 Honda CVCC Civic, the tiny collectable
1994 F350 4x4 crew (soon to receive the cummins)
2003 Tacoma DC, the wifes/camping
1983 John Deere 310C (Backhoe, for work)

On the 617.95 engine, there is a bypass passage in the thermostat housing that serves that very purpose. Following the FSM-prescribed fill procedure makes it happen a lot faster.

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When cryptography is outlawed, bayl bhgynjf jvyy unir cevinpl.

The point that you miss, dear TF, is the fact that the 80 degree thermostat MIGHT be defective. Putting in the 70 degree thermostat can accomplish two bits of data:

1) Confirm or deny the possibility of a defective 80C. thermostat. If the engine runs at 115C. with the 70C. 'stat, we both know the answer.

2) Confirm or deny the suspicion that the current crop of 'stats runs near the top end of the range. If the engine runs at 85C. with the 70C. 'stat, we both know the answer.

So, the 70C. 'stat can absolutely be part of the solution.

Thanks Brian, the exact point that I have been trying to get across to our wondrous friend TF... Not that it will get through

__________________
Jake, 15 years working on Toyota's for a living, self employed now- Landcruiser restorations.
1985 W123 300D CA emissions, 225K miles; deleted cat/oxidizer, all EGR removed
1997 Supercharged 4runner desert buggy
1993 Cummins D250 ~250hp 650 ft lbs, keeping it mild
1978 Honda CVCC Civic, the tiny collectable
1994 F350 4x4 crew (soon to receive the cummins)
2003 Tacoma DC, the wifes/camping
1983 John Deere 310C (Backhoe, for work)

In post #26 I made it no less than crystal clear that I believed the new thermostat was likely defective.


I know that you are enough of a scientist to know what happens to "data" when there is no control group.

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When cryptography is outlawed, bayl bhgynjf jvyy unir cevinpl.

It's like I'm listening to the Costanzas...

Let's not lose sight of the whole point of this thread. I'm genuinely curious as to what the outcome is going to be.

ElJaco, I didn't sift through every single post, but I'm curious: did you run your AC at all when the car was getting this hot? That's a huge concern of mine with spring/summer just around the corner. With the car running hotter, I'm concerned that running the AC will push it above 100C.

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Never be ashamed to ask for help.

1985 300D
1987 300SDL
1970 Jaguar E-Type OTS
2002 Dodge Intrepid (Traded In)
2011 Ford Crown Victoria

I completely understand the point that you think you are trying to make. Yours is a very common misconception; I hear it frequently. Everybody and their brother thinks that a lower-rated thermostat is the answer to an overheating condition. It isn't.

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When cryptography is outlawed, bayl bhgynjf jvyy unir cevinpl.

100C is well outside the control range for either a 70 or 80 degree thermostat. What is there to be curious about?

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When cryptography is outlawed, bayl bhgynjf jvyy unir cevinpl.

Pull quote of the year right there! Well Done

I don't blame you for not sifting through this mess

I ran the a/c and it was 83 degrees out, the a/c is what pushed it higher than I even wanted to see. My AUX fan works like a champ, I tested it and have seen/felt it come on a few times.

I also took the t-stat out today and boiled it, it is faulty. I am going to have a 80 and a 70 by weds, going to start with the 80, if It reads higher than it did before the swap, I'll try the 70.

__________________
Jake, 15 years working on Toyota's for a living, self employed now- Landcruiser restorations.
1985 W123 300D CA emissions, 225K miles; deleted cat/oxidizer, all EGR removed
1997 Supercharged 4runner desert buggy
1993 Cummins D250 ~250hp 650 ft lbs, keeping it mild
1978 Honda CVCC Civic, the tiny collectable
1994 F350 4x4 crew (soon to receive the cummins)
2003 Tacoma DC, the wifes/camping
1983 John Deere 310C (Backhoe, for work)

I have not read the whole thread, but I have found in the last 3 or so years thermostat quality varies regardless of brand. So it is important that you pot test it before you install it. I would not install a thermostat blindly ever again, it's just asking for a headache.



.

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1983 123.133 California
- GreaseCar Veg System

A controlled group would be excellent, but the best we can get is a single data point. The data from that single point might be inconclusive............but, might suggest a solution.

One can only try. There is no harm in using either the 80C. or the 70C. stat. Both will provide data. Personally, I agree with you that the 70C. stat cannot solve the problem of 115C. temperatures. However, it might possibly solve the problem of a defective 80C. stat if it runs at 80C. It would further confirm ongoing suspicions that the current crop of 80C. 'stats generally run near the top of the specified range.

This thread now has me worried about putting a new t-stat in my OM606.910, it currently runs at a perfect temp and all seems to be operating well, but I do plan on taking it down to the desert this summer so I know it's best to do a good coolant flush and replace the t-stat as it has been a couple of years. What brands are you guys finding to be the worst offenders these days? Behr, Wahler?

Well I've probably changed, 500?+ thermostats in my life, I dunno how many, but this is the first one that I have had be bad. It takes what, 15 minutes to change a t-stat, and 10 to boil one, so for me, it's not worth my time to test every one.

__________________
Jake, 15 years working on Toyota's for a living, self employed now- Landcruiser restorations.
1985 W123 300D CA emissions, 225K miles; deleted cat/oxidizer, all EGR removed
1997 Supercharged 4runner desert buggy
1993 Cummins D250 ~250hp 650 ft lbs, keeping it mild
1978 Honda CVCC Civic, the tiny collectable
1994 F350 4x4 crew (soon to receive the cummins)
2003 Tacoma DC, the wifes/camping
1983 John Deere 310C (Backhoe, for work)