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Are Temp. Gauges Reliable?

In the past dozen years or so, I’ve noticed that the coolant temperature gauge on cars I’ve owned (Honda, Acura, Mercedes) never varies, even slightly, once the engine is warmed up. This seems to be true even when conditions are extreme. Example: two summers ago, I was trapped in a huge traffic jam on the beltway around Wash. DC. The temp. was 101 deg. and my A/C was going full blast. I inched along for over 2 hours but that darn temp. gauge on my Acura TL never moved! I know modern cars have radiator fans and effficient coolant circulation, but it’s still difficult for me to believe that the engine temp. didn’t increase some that day. On the other hand, why would Honda engineers design this gauge to lie to us?

They didn’t design the gage to lie. They designed the cooling system to be able to maintain a constant temperature even under extreme conditions.

Recognize too that the outside temp was 101F, but the engine is operating at 200F+. The cooling system isn’t trying to keep it below the ambient temp, just at some specified temp about 200F. Any properly operating cooling system should be able to do that without problem.

I’ve noticed the same thing on my Civic’s temperature gauge, and I believe it is accurate based on how it moves as the car warms up. I believe it is simply a matter of better engine design and temperature regulation. Precisely managing engine temperature makes for better fuel economy and engine longevity.

The guage is likely accurate. It might be nice if they had some numbers on the dial but that might be too precise for some. The thermostat keeps modern motors at the optimum temp so that efficent combustion occurs and this helps control pollution coming out the tail pipe. If the guage goes from the center up to 3/4 of the way to hot then you have a cooling problem. Yes, electric fans are very good at cooling the motor in stop and go traffic. The old fashioned fan on the water pump needed the motor running at above idle speed to move enough air to cool the radiator.

In today’s cars once the coolant is at operating temp and then goes higher the electric fans kick in. With the AC on there is a always an electric fan running in most cars.

I’ve read (but cannot remember where) that some of the gauges are now 3-position gauges: cold/OK/hot, without actually showing temperature. I’ll see if I can find anything to back that up.

Mine doesn’t show degrees, only cold/OK/hot. It’s analog, but without actual readings.

It’s okay though. Readings other than cold/OK/hot for this purpose are really just clutter.

I think having the air conditioner on may have helped, since that would have caused the fan to run constantly. In my car, if I run the A/C, the temperature doesn’t get higher when I stop. Without the A/C running, the temperature climbs somewhat high before the fan turns on, and then the temperature returns to normal. The fan seems to be able to maintain normal temperature if the car isn’t moving, so when the car is stopped the temperature depends on whether the fan is running.

Wxf048, I’d suggest that you have you cooling system looked at, and perhaps the fan’s temp sensor tested. Your system should not be climbing and dropping like that.

Wxf048, what do you drive? I don’t believe it’s normal for the temperature gauge needle to rise like that. You might have a looming problem that could become worse.

I appreciate all comments. At least wxf048’s gauge moves a little. You know, I owned a Mercedes in the 80s. It had a big temp. gauge. with a broad sweep. I really trusted it because it would drift around a little. On cold mornings, I wouldn’t turn on the heat until the engine warmed up. When I did, I could actually watch the dial drift down a tad as the heater core pulled heat from the coolant, then return to normal a few seconds later. Maybe modern gauges are programed not to move from the norm unless the coolant temp. changes a certain amount, say 10 deg F.

There’s a difference between reliable and accurate . Yes the gages work but are they accurate - not so much !
Yes modern gages are programmed with a ’ dead zone ’ where the needle will stay still even if the temperature moves a few degrees ! It’s called a heavily damped gage .

Nice catch Genex. Although most of us try not to quibble about wording, there truely is a difference between reliabiliy and accuracy.

I have a 99 Cavalier. It’s done that since I first got it 8 years ago. My first car (an 86 Hyundai) did the same thing. I always thought it was normal, but other cars I sometimes drive (all newer than mine) never report warmer than normal. I’m going to get out my scanner and watch the digital readout while the car sits idling after being warmed up. I’m interested in the comparing gauges, digital readings, and fan on/off settings on a couple of cars.

I’ve seen that gauges fluctuate on many cars, but as far as I can remember, nothing newer than about 2000 (which, btw happens to be the year I moved back to the US). What wfx048 is experiencing was quite normal for my corollas (76 and 79, RWD, converted to electric fans), a friends Lumina, a couple Tercel’s, and various other European FWD cars (Fords, Renault’s, Volvo’s and a smattering of other makes).

In addition to a gauge that actually has more than the OK or not positions, the thermostats would operate with more flexibility in their open/close states.

My results were interesting. My mother’s 01 Prizm showed its normal gauge position (just below half-way) at the thermostat temperature of 180. It basically didn’t move between there and 207, when the fan came on and pushed the temperature to 194. Another cycle showed the same results. This seems to be what’s expected.

My Cavalier got to its normal gauge position (just below half-way) at its thermostat temperature of 180. By the time it got to 196 the needle was noticeably higher (above half-way). It heated all the way to 225 before the fan came on. The gauge was within the normal zone, well below the red zone, but I’m not sure I like it getting that hot. I don’t know where to find the specs. The fan didn’t want to turn off. It cooled the engine to 174 and was still running. Either the thermostat or the still-100-degree temperature kept it from getting cooler. The fan didn’t turn off until I drove the car a few blocks. By then it was up to 176, but the fan was off.

I’m not sure what to make of that.

The more systems get in control of the cars computer, the more quickly it can respond to the cars needs. I feel this is one of the big reasons car’s heat gauges seem to remain more constant and operate in the most efficient range. There is a big advantage to doing this.

Consider yourself lucky. I had a '92 Civic with a temp gauge that started redlining for no good reason. I’d be at a stoplight and I’d look down to see it rising from its usual “just above center” position to peg itself at the top of the range. When the light changed and I started moving it would drop right back down again. Never any smoke, never any steam, no symptoms whatsoever except that the temp gauge had suddenly been possessed by the devil. When I took it in to have the “overheating” problem worked on they kept telling me that nothing was overheating.

dadoctah, I strongly urge you to try another shop. What yuo’re describing is not normal and if continued could lead to destruction of the engine.

Ther are numerous tests that should have been performed, starting with an operational test of the cooling fan and a test of its temp sensor. Flow testing and thermal mapping of the radiator, testing of the T-stat, flow testing of the water pump, testing of the radiator cap, and even checking of the radiator hoses for a collapsed inner liner are all thing thing sthat should be looked at.

Shops that neglect to look more deeply into an issue as potentially serious as this just because the engine doesn’t overheat in front of them are, IMHO, derelict in their duties.

My old 94 will climb a little above normal if the A/C isn’t on and the engine is idling, then the fan kicks in and it drops. It’s always done this, and never comes close to overheating, regardless of the outdoor temperature or driving conditions. If the A/C is on with the low-speed fan running constantly, the temp gauge is pretty much painted on.

In the early ninety’s you could watch a tempuratue gauge during engine warm up and see it climb to 205 F before the thermostat opened, then a surge of cold coolant would bring the gauge down to 180 F. The temp would then settle at 195 F.

During the spring customers would complain thier car was running hotter than normal, the radiator fan comes on at 220 F.

The late ninety’s brought electronically controlled instrument clusters (analog gauges) allowing to mask any normal temp movement, as genex stated with a “dead zone”. The gauge is designed to stay in the near center for temps between 180 and 230 F. While monitoring the temp with a scan tool I unplugged the radiator fan to create a high temp situation, the temp gauge would read normal until above 230F, then increment up in steps until 250 F, then the gauge would pop into the red. This is effectively dumbing down the gauge to a warning light, it will display a cold or hot value when the temp is abnormal.