Thermostat too cool / out of spec / wrong part?

[VeryNoisyPoet]

Car in my sig. Warms up plenty fast, but coolant temp seems to swing lower than it should when on the highway or with the AC fan running. Even on a hot day, my Scangauge reports coolant temps consistently around 82C / 180F when cruising, or if the AC fan is running. When AC fan isn't running in slow moving traffic the temp cycles normally between 96C/ 204F (radiator fan shuts off) and 103C / 217F (fan turns on).

Thermostat was replaced maybe 7 years ago with what should have been an OEM unit rated at 87C / 189F. System was flushed and filled with all new 50/50 mix as of a few weeks ago. Old coolant came out green with a little brown tint and a few little flakes came out with the flush, but otherwise system looks spotless inside.

I thought rated temps on a thermostat indicates when it begins to open, plus or minus a couple degrees, so it almost looks like either I have an 82C/ 180F thermostat installed by mistake, or the OEM thermostat is pretty far out of spec on the cool side.

Any thoughts on this? New thermostat is only $12 and super simple to access so I'm tempted to just replace it anyways.

 

[carviewsonic]

Replace it, it's getting weak. Replaced a few on my cars over the years, the old ones were acting just like the one in your description.

 

[Warstud]

The T-Stat in my truck runs about 15 deg cool. I need a new one.

 

[Kira]

Is "Factory Part ONLY" still the battle cry for thermostats?

Is there a quality aftermarket name in thermostats?

I used to think AC Delco was all quality stuff but I've been reading here that even they are repackaging goods made on lower quality lines.

OBVIOUSLY it's not worth risking buying a cheap stat in order to save a couple of bucks.

 

[VeryNoisyPoet]

FCPEuro lists four options:

- Genuine Volvo 90C for $23
- BorgWarner 90C for $11
- Mahle 92C for $11
- Vernet 87C for $11

All of them claim they meet stringent performance and reliability tests, and FCP makes a big deal of only selling quality parts to avoid the fitment and performance fails that often plague aftermarket items.

 

[threeputtpar]

If you do buy from FCPEuro, they do have a lifetime warranty. if it's as easy as you say to replace, then just throw a new one in there.

For my allroad, where a thermostat replacement includes a full timing belt job, OE is the only option. I don't want to be back in there weeks later due to a bad out of the box stat.

 

[SHOZ]

I replaced two t-stats for doing the same thing last summer. They would ride at the 180F opening point but seldom go higher. Now they run around 185F-187F. Fully open is 204F and when the low speed fan comes on for engine cooling.

 

[Quest]

why dread over a 7+yrs old thermostat?

 

[eljefino]

Not all of your engine is going to be the same temp. If the coolant temp sensor is far from your thermostat you could pick up or lose heat by the time the coolant gets there. Could be a bias engineered in, in other words.

That said, mine match right close, except on an old dodge k-car with the condition I describe.

 

[VeryNoisyPoet]

Originally Posted By: eljefino
Not all of your engine is going to be the same temp. If the coolant temp sensor is far from your thermostat you could pick up or lose heat by the time the coolant gets there. Could be a bias engineered in, in other words.

That said, mine match right close, except on an old dodge k-car with the condition I describe.


Temp sensor probe is right next to the thermostat on these engines, so it sees the hottest water in the system.

Good tip for some other vehicles, I imagine.

 

[VeryNoisyPoet]

Originally Posted By: Quest
why dread over a 7+yrs old thermostat?


Dread isn't quite the right word here. This is a curiosity thread to get input from lots of other people with lots of combined experience, as I only have a few years experience working on just a couple vehicles.

 

[VeryNoisyPoet]

Originally Posted By: threeputtpar
If you do buy from FCPEuro, they do have a lifetime warranty. if it's as easy as you say to replace, then just throw a new one in there.

For my allroad, where a thermostat replacement includes a full timing belt job, OE is the only option. I don't want to be back in there weeks later due to a bad out of the box stat.


Yikes! I wouldn't want to do that job twice either.

 

[SHOZ]

My Gen Coupe has a unique cooling/thermostat setup. The temp sensor is at the back of the head in a manifold where the coolant is coming out of the engines, so it's the hottest the engine sees. Out of this manifold one end is the upper radiator hose and there are two smaller hoses, one goes to the heater core and the other goes to the back of the t-stat housing in the water pump. The heater core one then goes to the base of the t-stat which is connected to the lower radiator hose.

What I found is in the winter when you are pulling a lot of heat out of the heater core this coolant is then below the t-stats opening temp. It actually drives up the entire cooling system temp about 5F or so at the time you want it the most.

I figured it's a fluke and Hyundai engineers didn't plan this to work this way.

The t-stat range is 180F open and 204F (also the low speed fan turn on temp) fully open. When fully open the base of the t-stat will close off the other small coolant hose coming from the head. This stops the flow of that coolant past the t-stat base and also forces more out through the upper radiator hose.

 

[das_peikko]

Go to dealer and get a factory thermostat. That's one item I don't mess around with by going aftermarket.

 

[97prizm]

I've always like the Stant super stat thermostats. They ate a bit more but are USA made and seem to hold up

 

[VeryNoisyPoet]

UPDATE: New thermostat arrived and I'll install it tomorrow. I went with the 90C / 194F BorgWarner unit since the Genuine Volvo unit was the same thing except a $10 markup.

I tested it in a pot of water that I slowly heated up with a temperature probe. I could just see it crack open at 91C / 196F, and it looked pretty wide open by 100C / 212F (see image). I cycled it a few times, so at least it's not a dud out of the box.

 

[VeryNoisyPoet]

New thermostat installed, and problem solved! Temps don't go below 89C / 192F anymore.

Old thermostat was actually a 90C / 194 F unit, so it was opening a full 10C too early by the looks of things. No obvious fouling or corrosion, so I guess it was just tired.

Also a good sign is how clean the inside of the housing and passages look. Temperature sensor can be seen towards the top of the housing in the picture. I scraped and sanded smooth all mating surfaces before installing the new thermostat, and torqued the bolts to 12 ft-lbs.

 

[Lapham3]

It appears as nicely accessible on your car. I've had the most problems with simple thermostats and radiator caps being 'bad from new'. So, I don't time change these and often get decades of service with good ones. Yes, I have cars that I've owned for 30-40 years, some from new or nearly so. Some of the cars these days are scary with changing such a basic part.

 

[VeryNoisyPoet]

Originally Posted By: Lapham3
It appears as nicely accessible on your car. I've had the most problems with simple thermostats and radiator caps being 'bad from new'. So, I don't time change these and often get decades of service with good ones. Yes, I have cars that I've owned for 30-40 years, some from new or nearly so. Some of the cars these days are scary with changing such a basic part.


Yeah it's surprisingly affordable and easy to work on for a modern-ish European car. Toughest part was breaking loose the two T40 bolts, since I've had bad luck with old Torx heads stripping out. These ones were in good shape, but I still needed penetrating oil, some massaging with a small impact driver, and my breaker bar to get them moving.