Thermostat Failure?

[The Critic]

During my commute this morning, I noticed that my temperature gauge was reading a hair above 1/4, even after an eight mile long highway drive. In addition, the heater's performance seemed to be much worse than usual. If I recall correctly, the gauge usually reaches the 3/8 mark very quickly (within a mile of city driving), but that was in warmer (60F) weather. This morning, the gauge was barely at the 1/4 mark as I entered the highway after two miles of city driving.

The outside temperature was about 40F this morning. I'm not sure how long it is supposed to take for gauge to reach the 3/8 mark in this weather. However, the gas mileage suddenly dropped 1.5 mpg at today's fill-up compared to the previous two, so coupled with the lousy heater performance, I think something is amiss.

Since the Saturn already has 121k miles, I went ahead and ordered a new Stant 195F thermostat along with new Gates upper and lower radiator hoses. I've already replaced the engine coolant temperature sensor with the updated dealership part, so I'm certain that the gauge is reading correctly.

Do you folks think the thermostat is the problem here?

Thanks.

 

[HTSS_TR]

Yes, the thermostat failed at open that why your coolant temperature is lower than normal and a drop in gas mileage.

 

[ThirdeYe]

When my thermostat failed on my Acura, it would hardly show any temperature while I was driving at all, but if I stopped and let the car idle it would come up to temperature... that's what typically happens if it's stuck open at least.

 

[oilyriser]

Bit above quarter mark is normal for Saturn, in cold climate, when coolant reaches 80C, but the stat is probably opening early by that age and the motor is taking too much time to reach temp. Don't be disappointed if the new thermostat makes no difference in the final temp gauge reading, once it warms up.

 

[The Critic]

Originally Posted By: oilyriser
Bit above quarter mark is normal for Saturn, in cold climate, when coolant reaches 80C, but the stat is probably opening early by that age and the motor is taking too much time to reach temp. Don't be disappointed if the new thermostat makes no difference in the final temp gauge reading, once it warms up.

To clarify, previously the gauge would read exactly between the 1/4 and 1/2 marks, and it would reach that mark after a very short period of city driving. Now, the gauge pretty much stays on the 1/4 mark (a hair above was a bad descripition) and it takes much longer to get to that spot. So are we certain that this could not be caused by cold weather alone?

Either way, the parts are already on their way so I'll have to install them. Given the age and mileage of this car, it's probably a good idea to replace them for preventive maintenance anyway.

 

[demarpaint]

Sounds like the T-stat. I found that some cars I've owned a OEM T-stat worked better that the Stant replacement did. Not sure about Saturn though. The difference in temps between 60 and 40 is not really that cold. If we were talking between 60 and 20 it might delay the opening a little longer. But the temp range you mentioned is only going to amount to sllllllllightly longer time to open.

I have a feeling your T-stat is stuck open or not fully closing and opening too soon, if it were failing to open you'd overheat.

Frank D

 

[StevieC]

Make sure when you get a new Thermostat that you get the fail-safe version. This way when it fails all you get it no heat, or a cold running engine and it will always get you home.

If you buy the cheapie you could risk over-heating the engine and cause damage and will have to pull over and wait for a tow-truck.

The difference is about $6 here...

 

[Donald]

Originally Posted By: HTSS_TR
Yes, the thermostat failed at open that why your coolant temperature is lower than normal and a drop in gas mileage.


Actually its just the opposite. The thermostat is stuck fully open.

 

[Donald]

Clearly in your case when you remove the thermostat from your cold engine you should see it mostly or fully open. If its closed then maybe there is something else.

You can test a thermometer in a pot of water with string going side to side hanging the thermometer in the water (but not touching the sides or bottom of pot. You need a thermometer to measure the water temp.

While in theory the thermostat should make the gauge read the same in winter or summer assuming the radiator can properly cool the engine in the summer and the engine can supply all heat to cabin in the winter. But in most vehicles the gauge does read lower when it gets colder.

When it was 40 you probably had the heat on and when 60 probably not.

Bottom line is a thermostat should be considered a maint. item and replaced every few years anyway, so you are due.

 

[StevieC]

It should be replaced when it is needed. In my last car it was over 10 years old and I never replaced it... Don't fix it if it ain't broken in my opinion...

Also if your car is Japanese or import, buy it from the dealer. In my opinion they are much better quality and will last a very very long time versus the generic brands you can get at a local parts store.

 

[Rhymingmechanic]

A new thermostat solved that same problem in my Saturn. When I put the old one in boiling water, it opened but never closed again.

One more hose you could replace while doing the job is the "pipe to water pump" hose. NAPA should stock it. The pipe end connects with a clamp rather than a crimped collar.

 

[Spector]

If not the thermostat then the sensor for the gauge and last resort, the gauge itself.

I have two cars that once the thermostat was replaced the gauge never read the same again, replaced the sending unit etc, always read lower from that point on. You may have to adjust your mind to know it will read lower and at what point it will now be considered overheating.

 

[Donald]

He also mentioned lower heat output in the cabin, so one would assume its not the sender or gauge.

 

[The_Jeff]

Critic, be sure to take the time to get pictures of old part next to new: I bet the rubber seal is rather chewed up and shot, allowing bypass.

 

[mechtech2]

Right.
Get a good one. Ask for the most expensive or best quality one at the auto parts store, or get a factory one at a dealer.
This is money well spent, and only a few bucks more.
Also, don't get a colder one, use the factory rated type. This will keep the thermal efficiency up there for cruise conditions.
The temp rating is the STARTING opening point, BTW. It needs more heat to get it open fully.

 

[The Critic]

Thanks guys.

I ordered the Gates #14279 thermostat from RockAuto, it was $16.86. It was also the only one available.

 

[StevieC]

I'm not familiar with Gates as I have never seen them in Canada. But judging by the price it should be a good one that is a fail-safe. Did you get a gasket to replace the other one? Gonna need one of those too, but you can source it at a local parts store.

Make sure you let the car warm up for a 10 minutes with the radiator cap off (so as not to build up pressure), and then shut off and replace the thermostat.

By warming up the engine a bit first will allow the bolts around the thermostat housing to come out much easier and help to prevent stripping the bolts. DO NOT OVER TIGHTEN THE BOLTS when you put it back together...

Cheers Buddy!

 

[sprintman]

Mines gone in the BMW. Told this morning it needs thermostat, expansion tank, hoses and coolant. Luckily I have steel impeller water pump unlike earlier model which has plastic otherwise I'd need that to. BMW's are fun!