This spring when I went to the parts house to buy a new summer (180F) thermostat, I thought I would splurge and buy the more expensive "fail-safe" model from Motorad. Well, life this fall has turned out to be much more challenging than normal, and I had not found the time to change to my winter (195F) thermostat. But I was not too concerned, usually a 180 thermostat makes plenty of heat.

The weather here in Ames turned pretty cold last week and we needed to make a quick 180 mile trip to Minnesota. I started the '95 SLE and let it idle with the defroster and heat on high to help loosen the 1/2" of ice that had accumulated over the car. In a period of about 20 minutes with outside temperatures less than 20F, I got the car cleaned off and away we went. As we pulled out, the temperature gauge was reading about 200F from the long idle. As we drove up the interstate, the temperature gauge kept dropping, finally coming to equilibrium just over the 100F line. The air from the heater got colder and colder as I increased the heater temperature control to maximum.

When we returned from Minnesota, I removed the summer thermostat. Here'* what I found:


Wide open and locked in that position by a little brass tang. The extended idle had increased the temperature enough to pull the thermostat flange past the "fail-safe" tang, locking it open. Now, this is not supposed to happen until the engine has "overheated." I have not been able to find what temperature is defined as overheating by MotoRad, but as I cleaned off the ice, I do not remember hearing the cooling fans engage. Although I was not watching it closely, I estimate that it locked open somewhere between 200 and 220F.

Here is an image of the other side showing the temperature rating:


I Googled this issue and found others had experienced the same problem of the 180F fail-safe thermostat locking open at temperatures well within normal operating range.

I don't think I will be buying any more of these.

Bill, what were the advertised advantages, if any?

It is designed to protect your engine against overheating damage caused by a stuck-closed thermostat. When the engine overheats, the flange opens wider than normal and pushes past one of the brass tangs which snap over the edge holding the thermostat open. This provides maximum cooling for the engine. It is not a bad idea, and it obviously works. I'm just thinking that the accuracy of the "overheat" temperature may not be all that good.

Thanks for the information. I don't think i'd want one either. Did you freeze during the trip?

Bill, I had the exact same issue TWICE with our 99 SE. Never bothered to post about it. But, I did the same thing. Thought I'd be wise and spend a couple extra bucks to protect my engine IF the thermostat ever failed. Bought the same model as you. The first one failed within 3 months. I got it replaced under warranty. The second one failed after about 6 months. I'm not even sure if it was under warranty, but I pitched it and bought a conventional 'stat. I ran the conventional model for about 16 months (until we sold the car) with no issues.

I feel your pain.

Well, let'* just say that I was never in danger of falling asleep at the wheel.

Fuel economy dropped from about 28mpg to 22 also.

There is a lesson here. No matter how trivial some issue may seem to be, if it relates to our beloved cars and their operation, a quick post might save some other member some time and grief. The lifeblood of this forum is contributions from the members.

I had the exact same problem with the exact same thremostate and it was also drilled. I removed it and istalled the original 195 stat and I have amazing heat now. I reset the 180 so it'* not constantly open but I don't know if I'll install it in the summer again.


Thanks for the wright up Bill.

Yeah, I reset mine, too. But, what'* the point? If the thing is gonna snap open again within the normal operating range, I'd be right back where I started. The fact that the thermostat was drilled is an interesting point. That should have made it a little more difficult for the thermostat to pull into it'* "overheat" range, as a small amount of coolant would have been passing through the flange at all times providing a bit more cooling for the engine than an undrilled thermostat would have. But, the thing locked open anyway. I'm thinking the best place for it is in the garbage.

I might consider using one of these if I had a more sensitive engine (aluminum heads) for which I wanted to provide extra protection. Maybe I will try to contact MotoRad to see what the theoretical snap-open temperature is for their different models. I suppose that the 180 might be more prone to this problem if the snap-open point is a fixed number of degrees above the nominal temperature, say 40 degrees. In that case, a 195 might work OK with our relatively high fan-on set point.

Bill,

A few weeks a go when I was repairing the UIM/LIM failure, I went to AutoZone for a Thermo and the counter help showed me that same thermo. Something told me not to get it. Guess I made a good choice. Sorry your ride was a little cooler than you wanted. IMHO thermo'* are better than they used to be - that is not as many failures. I usually buy the more expensive one'* hoping that it wont fail. At least it didin't over heat