Engine temp gauge & idling in heat

[Ramblin Fever]

is it normal, on a 100F day for an engine's temp to rise to 3/4 idling for 20min or so with the A/C on??

The gauge never went above that, but the minute I realized it was at the half-way mark, I shut the A/C off.

The minute I got the truck rolling, where it could actually pull in air, the gauge dropped back to norm pretty quickly.

Truck has new radiator, waterpump, coolant, etc.

This was the first real hot day and there was no movement of outside air circulating for the truck to pull in at the time. 2 different mechanics I called just out of curiousity said it was normal as long as it didn't actually overheat....which it did not.

 

[Colt45ws]

Unfortunately, the dumbing down of gauges has resulted in units that are scarcely better than a 'idiot light' for actually telling you what is going on.
So, maybe? I dont even know what year, make, and model you speak of.

 

[SLCraig]

GM? If so, they like to use scare tactic gauges and make people think their cars are overheating.

Take Saturns for example, my car finally turns the fan on at 3/4 on the gauge, getting close to Max (this is normal) on the even older Saturns the gauge almost gets pegged before the car turns the fan on, and this is actually normal operation. Stupid if you ask me, but normal. Seen this on other GMs as well.

 

[SteveSRT8]

Gauges vary wildly from car to car, even on the same model.

Manufacturers often change the face and/or calibration to mask true readings. And most drivers are worried about high readings when the engines run fine at the elevated temps.

Get a real gauge on it and learn how the readings correlate, then you can drive with confidence. I use an old mechanical gauge and strap it to the outlet hose on the radiator, drive it for a few days and then take it off.

 

[Nick R]

Originally Posted By: SLCraig
GM? If so, they like to use scare tactic gauges and make people think their cars are overheating.

Take Saturns for example, my car finally turns the fan on at 3/4 on the gauge, getting close to Max (this is normal) on the even older Saturns the gauge almost gets pegged before the car turns the fan on, and this is actually normal operation. Stupid if you ask me, but normal. Seen this on other GMs as well.


Yup, when the fan is working normally, mine does this too. If the A/C is off and I'm stoped or in stop-and-go traffic the fan won't come on till the thermostat hits 210. Which is most of the way to the top of the gauge.

 

[The_Jeff]

Originally Posted By: SteveSRT8
then you can drive with confidence. I use an old mechanical gauge and strap it to the outlet hose on the radiator, drive it for a few days and then take it off.


That's going to give you some wild readings, on the cooled side of the thermostat.

 

[Ramblin Fever]

Sorry.. the truck is a 97 Isuzu Rodeo with the 3.2L V6 Isuzu engine, not GM.

The thermostat is a 175, IIRC.

Fantastic engine and very stout.

 

[Chris142]

It's going to run warmer when it's not moving down the road. How is your fan clutch?

 

[mechtech2]

Sounds normal.
But it is always good to check for leaves and debris that block flow in the condenser or radiator.

 

[severach]

Leaving the AC on would keep it cooler. The AC forces the electric fan on.

The heat goes up and down between the fan set points and the thermostat settings. At highway speed the temp should stay on the thermostat setting. At idle the temp will increase to where the fan comes on and decrease to where it turns back off leading to a large needle swing. The swing can be as high as 180*F - 215*F and so long as you aren't really over heating is perfectly normal so long as your cooling system is in good condition. A marginal cooling system could burst at the elevated pressure.

 

[SteveSRT8]

Originally Posted By: eljefino
Originally Posted By: SteveSRT8
then you can drive with confidence. I use an old mechanical gauge and strap it to the outlet hose on the radiator, drive it for a few days and then take it off.


That's going to give you some wild readings, on the cooled side of the thermostat.


Nope, if you position it properly it's [censored] near dead on. I check with my infra red thermometer gun. But ya can't do that while driving!

It does require a bit o' smarts to get it strapped down tight on the correct side, but I was assuming everyone here knew that. I always check both the inlet and outlet actually.

 

[Chris142]

Originally Posted By: severach
Leaving the AC on would keep it cooler. The AC forces the electric fan on.


I don't think his truck has electric fans.

All engines with mechanical fans will run warmer sitting still than going down the road. He said that once he got moving it cooled down imediatly. This tells me that the rest of the cooling system is ok.


Owners manuals used to tell people to raise the rpm's when sitting still to increase air through the radiator. The OP can try a new fan clutch and see if that helps some but as I said it's going to run warmer sitting still anyway.

 

[Gary Allan]

Add a pusher electric up front; relayed off the compressor clutch.

 

[SteveSRT8]

now there's a good suggestion. And if space is at a premium in front, add one on the back side.

And not "all" vehicles with engine-driven fans get warmer while idling. Some are excessively shrouded and actually heat up at higher speeds due to the restriction.

 

[Ramblin Fever]

As far as I know, the cooling system's in superb condition. I've been VERY VERY adament about it the entire time we've owned this truck, since new, as it is an aluminum engine.

Going to take truck in for the steering box to be looked at....feels like there's some play while driving the truck...going to have the fan clutch looked at at the same time.

Fan clutch is in fact original, 197k miles worth. no fluid leaking and it doesn't feel loose, we checked that this morning, but I will have the shop double check.

 

[antonmnster]

Sounds like a weak fan clutch. I replaced the one on my BMW yesterday; no longer locked up after 140k. Made the electric push fan do all the work.

BMWs have the most dumbed down temp gauges of anyone. The needle will peg at the 12 o'clock position when the coolant is ANYWHERE from 160 to 235 deg. It really tells you nothing. If it did, then most all new BMW drivers would be hounding their service advisors to "fix" the car... morons.

Saab temp gauges sound just like Saturn's. You'd swear the car was going to burn up waatching the gauge, then the fans would pull it back.

One of the water-cooled Cushmans at work has a REAL temp gauge. It will shoot right up to 190, the fan will turn on, it will drop right to 170, and so on.

So it's normal to wander somewhat.

 

[rslifkin]

The temp gauge in my Jeep is a real gauge. Sitting in traffic with the A/C on, it stays pretty constant, as the fan runs most of the time due to A/C pressure (not enough condenser airflow). With the A/C off, it varies as the fan cycles based on engine temp.

What you're describing sounds normal for a vehicle with a mechanical fan only. It's possible that your fan clutch is a bit weak, particularly if it hasn't always done this.