Thermostat Stuck Open?

[RJS]

Hi

My engine has been running cooler than normal this year. During the summer, the temp gauge has been reading about 1/3rd up the scale (where the middle of the gauge = 180-185 degrees). Infrared temp gun on T-stat housing read about 165-170 degrees. At that time, I decided not to take any action and just observe.

However, with the cooler Fall weather, the dash gauge is now reading about 1/4th up the scale and the temp gun reads 145-150 degrees on the t-stat housing.

Is it possible the t-stat is stuck open - I always thought they failed closed? Short of removing it, are there any tricks/tips to "unsticking" it (i.e. rapping on the t-stat housing to vibrate it loose)?

Engine runs great. No other symptoms.

Appreciate any thoughts. Thanks,

Bob
PS: I believe this all started just after the last time I flushed the cooling system. Originally I thought the cool running was simply a benefit of the flush. Now I am wondering if a piece of debris was dislodged and stuck in the t-stat (holding it open)??

 

[sail]

I have been having problems with my cooling system. Driving more this summer at extended higher speeds the radiator gradually fills the overflow.

Using a 180 degree thermostat the gauge is on the high side. The heater would cook you out. Flushed the system, put in a 160, same problem. Now the gauge is about in the middle. Some heat but not nearly as much. Car seems to run fine after warm up but does not seem as hot as I expect opening the hood. I have raised the car to fill, took out the heat sensor till it overflowed, burped with bottom hose. I don’t think its air in the system.

So in my case I don’t know what else to do but take the radiator to a shop. In yours why not just pop in a new thermostat.

 

[SkinnedKnuckles]

I think failing open is part of the "fail safe design" some of them advertise. I had on that failed open 2 yrs ago with symptom as you describe. Far preferable to failing closed.

 

[RJS]

Richard,

Just lazy I guess... Plus, I want to confirm it may not be anything else before I go there. I note that Stant manufactures three levels of t-stat. The "Economy" version is what the big three sell. There is also an "OE Type" and a "Premium SuperStat".

o Stant SuperStat® premium 180 degree thermostat (PN 45358) "...uses a unique non-linear valve to stabilize engine temperatures, prolonging engine life and improving fuel economy and emissions." Interchanges w/ NAPA #530080.

If I do replace the T-stat, I'll go for the SuperStat.

Rich, in your case, the cooler t-stat (160) only sets the min temp for the engine but, has no impact on the max temp. Once the t-stat opens, the max temp is determined by the thermal efficiency of the cooling system (i.e. it's ability to transfer heat through the radiator). If that is not up to the job, you will likely run hot even with t-stat removed. Your improvement was likely the result of the system flush, not the 160 t-stat.

Be sure the air duct is in place (this is critical) and that the front of the rad is clean and not full of debris blocking airflow.

You can also try to increase the thermal efficiency of the cooling system by flushing the rad, and then refilling the system with a mix of 60% distilled water, 5% Water Wetter and 35% coolant. Water transfers heat MUCH better than coolant but, of course you cannot run 100% water (although some racers do). Very smart to raise the engine and burp all the air out too.

Bob

 

[jsfbond]

Failed open is the design of a good quality t-stat. Also your oil filter should have a by-pass valve in it, dirty oil is better than no oil.

 

[EV2239]

It could be nothing to do with the thermostat and just that the gauge could do with overhaul. They tend to read low for a time before giving up altogether.

Ash

 

[sail]

Bob, I am understanding the lower range is what the stat regulates. Summer and winter make a bigger difference than I would have guessed. But in both cases the temp held steady at moderate speeds and would rise slow but sure at speed as it spilled over. My guess is the 50/50 coolant can't circulate fast enough. Thanks I'll check out your superstat and for now just not go so fast.

 

[Geo Hahn]

"...uses a unique non-linear valve to stabilize engine temperatures...

I hate it when an engineer transfers to marketing.

I would check the actual temp by pointing an IR thermometer right where the sending unit is.

When replacing the thermostat I usually unbolt the housing from the head (the long vertical bolts) and loosen the top hose at the radiator, then pull all that out for further disassembly, cleaning and inspection on the bench. Good time to replace the top hose if it is at all cracked or tired looking.

If the new thermostat doesn't have a little hole in it I drill one -- doesn't have to be very big, maybe 1/8". I think that make filling & draining the system a bit easier.

 

[TR3driver]

Bob, just change the T-stat. If it stuck once, chances are that it will stick again. BTDT. The stat, gasket, and enough coolant to make up for the little bit you'll lose just don't cost enough to bother trying to scrimp.

Richard, FWIW, I've been fighting very similar problems for the past couple of years on my TR3. The radiator had been to the shop several times, and pronounced "fine". But after some questioning, the last time I told them to go ahead and open it up to rod out the tubes. They were totally amazed at the amount of crud that had been coating the inside of the tubes! Apparently not enough to block flow significantly (they tested the flow each time), but enough to block heat transfer.

Unfortunately, after rodding out all the tubes, it was leaking in multiple places, so they had to replace the core.

The weather has turned cool, so I haven't really had a chance to test it, but it is clear that the thermostat is controlling the temperature now.

 

[macilona]

follow up question to the initial post by RJS---I have the same experience w temp running low in the cooler weather. Is low temperature of any concern?? the engine runs fine---does it matter if the temperature stays in a low range? thanks

 

[SkinnedKnuckles]

Too low a temp won't allow the engine to run as efficiently as it should. As to harm? I don't know. Carbs may run a bit rich, oil additives may not be as active as they should. Guessing there. A thermostat change is one of the easiest operations there is - why put it off?

 

[Geo Hahn]

...does it matter if the temperature stays in a low range?

Yes, the engine needs to be hot for all sorts of reasons. The engineer-types here can enumerate them but for one thing any moisture/condensation will not get cooked off until the engine is hot. Also a hot engine is more efficient. And, lubrication will be better once everything is up to operating temperature. Plus, your heater (if you have one) will heat better.

Well, you get the idea.