Coolant Temp Gauge Question

[TallPaul]

Sorry no photo, but my 1999 Chevy one ton van chassis motorhome has a coolant temp gauge and I want to see if anyone knows how to interpret the tick marks that don't have a temp associated with them.

The gauge is divided into three major tick marks: left, middle and right. Between these are a sub tick mark and between each of the major and sub tick marks are three small ticks.

So the major and sub ticks mark off quadrants, with each quadrant subdivided by three ticks.

Anyway, only the major ticks are marked with a temperature. These are 100, 210, and 260. What doesn't make sense then is the first half the gauge is a range of 110 and the second half is a range of 50. So what do the sub ticks in the first half amount to. Would it be the same proportion or about 75 for the first quadrant and 35 for the second?

 

[rriddle3]

To the left of center, each mark represents ~14 degrees and to the right of center, each mark represents ~6 degrees. It's just the way the gauge was designed.

 

[TallPaul]

Weird that they would make the increment change halfway through the gauge, but your point (known for fact or guess?) is about as logical as my thinking which would be that the whole gauge is proportional the same way. In your description, the top of the first quadrant is about 156F, whereas in mine it would be more like 175.

Well, if what you say is true, this thing generally runs around 150F, which seems way too cool.

 

[rriddle3]

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...but your point (known for fact or guess?)...

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No guess, just simple math based upon the known markings that you listed.

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Well, if what you say is true, this thing generally runs around 150F, which seems way too cool.

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Without knowing what temperature thermostat you're running, I would agree. Seems that the normal range should be somewhere between the 6th mark and the middle.

 

[TallPaul]

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...but your point (known for fact or guess?)...

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No guess, just simple math based upon the known markings that you listed.

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Well, wouldn't it be easier for them to set up the gauge to be decreasing in scale evenly from bottom to top, than to have an even scale that suddenly decreases in the middle. I am more inclined to believe it is continuously decreasing, which would put my normal temp closer to 175 ish, which is much better. Guess the only way is to hook up a better gauge, maybe Autometer.

 

[Junior]

My quess is that the gage is not linear and the marks labeled with numbers are known points. It might be a way to get the gage to not move around so much after the engine reaches operating temp. That could panic the uneducated. Just like a lot of oil gages really only measure if you have pressure or not. If people saw their oil pressure gaguese going from 25 to 60 psi they might think something is wrong.

It is possible the 8 year old thermostat is tired.

 

[TallPaul]

Yes, moving gauges are not understood by some folks, typically those who have no idea what is under the hood, nor care, so long as they get where they are going in comfort and/or style.

Funny, the Chevy OP gauge is real and moves a lot, but this one does not go up and down with thermostat cycling. Whereas on the wife's Aerostar the OP gauge is a dummy gauge, but the temp, though not numbered, moves up and down with thermostat cycling.

Thermostat tired? I would think time is not a factor as they may sit on shelf (NOS) for a long time, but actual usage would be the main factor in tiring the thermo. My guess anyway.

 

[eljefino]

My cutlass ciera had this gauge style and regularly ran at 1/4 position. At 1/2 (212 indicated) the electric fan came on.

I would regard the stock gauge as a toy. I would actually be pleased that the area of most concern is magnified for more careful viewing.

I know you have a belt-driven fan so can't go by that. A scantool is the only way to know for sure.

 

[Gary Allan]

If I read your description correctly, it's just like my temp gauge on my TJ. It works out to have "normal" be just left of center.

Your thermostat is probably in need of replacement.

 

[TallPaul]

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Your thermostat is probably in need of replacement.

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Well, that's one thing I don't plan to tear into. Will have to take it to the shop. Guess that is the one glitch with a low mile, but aged vehicle: some things just don't like to sit around for a long time. Example is that the crank position sensor went out around 11,000 miles.

Thanks

 

[Junior]

I guess Gary's opinion on the thermostat being bad carries more weight than mine.

 

[TallPaul]

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I guess Gary's opinion on the thermostat being bad carries more weight than mine.

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You said possible, Gary said probabable.

But actually it was more the weight of two opinions. But Gary is known to be a very automotivated tinkerer and so he carrys a bit extra weight. I'm still not convinced, but plan to ask my mechanic.

A bad thermo and cool running would result in open loop and poor fuel mileage and acid loading of the oil, but the oil looks great after 4500 miles (on blotter) and fuel mileage is excellent for a 454 motorhome 8.75 mpg. My Ford 460s got at least 1mpg less. So those items seem to point to okay thermo. All depends on the true temp vs stupid gauge.

 

[Junior]

Just giving you a friendly ribbing. No worries.

 

[TallPaul]

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Just giving you a friendly ribbing. No worries.

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Gotcha.

Hey, so I asked my mechanic and showed him the gauge layout. He said that the tick between 100 and 210 is probably about the thermostat setting. Could be 180 but some motorhomes are set to 160 to run cooler.

Now here is why I like this shop. They do good work and are reasonably priced. The guy advised me on my coolant changeout procedure and took 7 gallons of used antifreeze (some from a different car) and dumped it free of charge. Now that's service.

 

[Anduril]

My Cavalier's temp gauge has 3 numbered marks at 100, 195, and 260. Coincidentally enough, pointing directly at 195 appears to be normal operating temperature. At idle it'll creep up one tick mark before the electric fan comes on.

In my gf's car (also a Cavalier), her gauge setup is totally different (a year older than mine) and does not have numbers. Normal operating temperature is directly in the middle, but the needle goes all over the place. If we're driving fast on the freeway (70+), you can actually see the needle move back to about the 1/3 mark. If she just comes off the freeway to a red light and sits there idling, it goes almost to the red before the electric fans come on. The car has never overheated or showed any signs of actually doing so, so we've both just learned to ignore it.

I don't much care what the actual engine temperature is (my Cavalier being the only car I've ever driven that tells you the actual temperature), but see the temp gauge as more of a relative thing. Drive your car for a while and you'll know what's "normal," then just use the gauge to see if something's not right.

 

[TallPaul]

Oh yeah, my F150 has a "guage" with no numbers. Just says "NORMAL." This one always sits around 1/4 the way over from the left edge. I never see the needle move for the thermostat, and I have had the thermostat frequently changed in that truck. Must be a dummy gauge.

 

[Gary Allan]

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Well, if what you say is true, this thing generally runs around 150F, which seems way too cool.

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Is the temp consistent when going down the road at highway speeds

without too much (but some) increase on grades?

Is it typically the same temp you see idling in the driveway when it peaks?

See if your garage pal has an infrared gun and have him hit the thermostat housing when your at your normalized gauge reading.

 

[TallPaul]

Off the top of my head it seems to be pretty consistent on the road just below the 1/4 tick, but I am going on a 200 mile trip tommorrow and will watch the gauge closely. Will report back Monday night.

 

[TallPaul]

Well I was a little bit off when I posted above, unless changing out all the coolant changed things, which I doubt. Anyway, took a 200 mile trip and it pretty consistently stayed on the tick mark above the 1/4 mark. So if the scale were 1-17 with 1=100F, 9=210F, and 17=260F (with 5 and 13 as mid points between these) then mine sits on 5 most of the time, except when I slow down to a near stop, then it climbs to 6 for a while. Also 15 and 16 are merged together as one big red mark. Anyway, looks like everything is all right. Still don't know actual temp though.

 

[Matt_S]

A scan tool, like a GM Tech II, would show the actual temp the computer is reading. The service manual was unclear about the workings of the gauge, though.