Funky Thermostats

[Oiluj]

My temp needle has always hung a bit to the right of the centerline on the dash gauge. Even though I have a high capacity aluminum radiator, my car always runs a bit warm, about 200 degrees F when measuring coolant temp in the radiator. I finally decided to do something about it.

So I bought a new 180 degree thermostat from MSA. To verify things were operating correctly, I removed the existing 190 degree thermostat, cleaned it, and put both thermostats in a pan on the stove. I suspended the thermostats on a piece of wire so they didn't touch the bottom of the pan. The 180 didn't open until 189 degrees, and the two year old 190 didn't open until 198 degrees.

Since both appeared off in the same direction, I decided it would be prudent to verify calibration of my electronic thermomerter. I checked it in both boiling water and ice. As a back-up, I compared it's readings to a regular thermometer. Both read exactly the same and were dead accurate.

Both my thermostats appeared to be opening late... So off I went Napa Auto. They didn't have a 175 degree thermostat, so I got a 160 degree. Sure enough, it didn't start opening until almost 170 degrees. I figured that is still better and installed it in the car. A temp check of coolant now reads 173 degrees, and the dash temp gauge needle rests a little to the left of center. I think a 175 degree would have been perfect, but I'll stay with the 160. I'd rather the engine run a few degrees cooler than warmer.

BTW, just for grins I just looked at some oil viscosity curves, and the small difference in operating temp makes no significant difference. I "might" be able to detect a small drop in fuel efficiency, but time will tell.

The real moral of this story is, check the operation of a new thermostat BEFORE installing it...

[Wade Nelson]

I've frequently found cars that are running 10-30 degrees hot aren't holding pressure in the cooling system. A quick pressure test and a new radiator cap solves a LOT of "running warm" problems. Frequently it's a single loose hose clamp that drips under pressure.

[Stanley]

Got a real Nissan 180 deg Thermostat at The dealership in Tucson about 2 years ago. Looked more well-made than the chain-store type, flows better according to some. One of the few parts they still had for a 240, about $17.

[AZ-240z]

Got a real Nissan 180 deg Thermostat at The dealership in Tucson about 2 years ago. Looked more well-made than the chain-store type, flows better according to some. One of the few parts they still had for a 240, about $17.

Also, if you compare a Nissan thermostat to an aftermarket, you will see that the Nissan thermostat opening is about 30% larger than aftermarket. Less restrictive/ better flow/better cooling.

FWIW

Dan

[rcb280z]

I had the same results when I replaced my thermostat with a genuine Nissan one. Heating problems went away.

[Oiluj]

I do recall the Nissan thermostat having a larger flow area, which should flow better.

The real point of my post is that it's a good idea to test any new thermostat before installing it to be certain it actually opens at the specified temperature.

I admit to being surprised to find all three thermostats were off almost 10 degrees. Enough so that I questioned & verified the calibration of my thermometer...

[djwarner]

I saw Carl Beck at a Cars and Coffee meet this morning. I mentioned that I thought my Z was running around 220 if the gauge is correct. He said the preferred temperature is in the 180-190 range. I knew the current unit was replaced by the previous owner and thought he could has slipped in the wrong unit. So after reading this thread and listening to Carl, I found a 160 degree thermostat at the local NAPA and dropped it in.

I based my estimate on the 120-250 range on the dial and estimated the centered tick mark was at 180, leaving 70 degrees to the right of the tick.

Well, the new thermostat allowed it to climb about 2 needle widths past the tick mark, estimating 190 degrees on the same basis.

I thought I had resolved the issue until I went home and heated the old thermostat on the stove. With my non-contacting thermometer, it cracked open at exactly 180 degrees. I repeated the test just to make sure.

Like you, I'm going to leave the 160 degree unit installed. It was the standard for many older engines. Just goes to show you that modern manufacturing tolerances beat 41 year old temperature probes and gauges.

One point though, you can run an engine too cool for reasons other than viscosity. Any non-operating car exposed to temperatures near the dew point will actually cause condensation to form in and on the engine. This is because the metal is subject to radiational cooling as well as conduction cooling through the air. Water will desolve into oil up to about 1% by volume and it will affect the lubricity of the oil. The oil has to be heated up to about 180-185 degrees to drive off the dissolved water. But this is oil temperature - not coolant temperature.

So even at 160 degrees coolant, the oil temperature should still reach the 180 degree level.

What amazes me is that the thermostat actually throttles the coolant temperature. This explains why I've never heard the fan kick in even in the 90 degree plus temperatures here in Florida.

Edited October 21, 2012 by djwarner

[grannyknot]

Oiluj, I have found similar results with late openings when testing OEM and aftermarket T stats in various makes but I almost always end up going with OEM because of the quality of the product. I have also tested my "laboratory thermometer" to make sure it is accurate, and it is. I always want more accuracy in the cooling system but since I have never suffered a summer over heat I have come to accept that 5-10 degrees doesn't seem to make that much difference on a street driven car.

Chris

[Oiluj]

My wife & I took a drive of about 70 miles in the Z today. The temperature in stop-n-go traffic raised to the center mark on the dash guage, about 180 degress. When moving, it quiclky dropped back to just slightly left of the center mark, which I previously measured to be about 173 degrees at the radiator.

Still, next time I'll try the Nissan part, (assuming it's still available).

[EScanlon]

Recently I had the same problem with Roadster.

After weeks of being convinced that the car was "close" to boiling over, (needle past the center point at 190 (marked) by at least two needle widths), I was convinced that any day now I would suddenly have a torrent of steam explode out of the overflow bottle.

However, somehow the engine ALWAYS performed well, and I never seemed to lose any coolant (except what I purged in relieving pressure).

So, last weekend I bought one of those infra-red thermometers and tested it with known items. ( Glass of water chock full of as much ice as will fit and water to the top is a solid 32 degrees Farenheit, in fact, this is one of the calibration points that gets used, the other being boiling water.) IR Thermometer read exactly what was expected.

Started up the Roadster, let it run until it read "HOT" and then checked the temp at various spots on the engine (thermostat tower, radiator hoses, head, etc.).

The result? I was running a rock solid 180 degrees (engine variations usually lower than the 180 of the coolant), while the gauge continued to report (210 +) a HOT condition.

So, my question to you guys is: have you checked the accuracy of that gauge?

FWIW

E

[Oiluj]

So, my question to you guys is: have you checked the accuracy of that gauge?

Yep. That was the first measurement I made. My dash gauge reads right at center mark when coolant temp, (measured at top of radiator), is just over 180 degrees.

Didn't think this post would generate this much interest...