Verifying Temp. gauge reading

[MarkC]

My aftermarket temp gauge usually reads about 190F when my Cherokee is at operating temp. I know there's a 195F thermostat in there, and I know normal temp for Jeeps is about 210F. I let it idle for quite a while recently to see at what temp the aux. fan comes on, which it did at about 215F. I'm pretty sure it actually kicks in at about 225 or so.
My question is, how's the best way to see what the actual temp is, vs. the reading on my gauge? If I stick a thermocouple into the overflow bottle, it's goin got be cooler than at the actual sensor back on the side of the block, isn't it? I hesitate to unscrew the sender and stick anything in that hole while everthing's hot.

God, I need to get a life....

 

[Gary Allan]

Mark

Can we assume that this is an OBDII Cherokee? Either way the dash gets its input via the "buss" and the PCM. The indication needle, if in error, can be altered (I think, the speedo can for sure) with the dealer's DRBII scan tool.

The PCM is turning on the fan on what it interprets from the temperature sensor. The rad temp can be much lower than the water temp at the thermostat housing where the sensor is located. If your thermostat is partially closed ..you could have the condition that you describe ..where the "normal temp" appears low but goes higher. On my TJ's the only time that needle is above 205 is when it's summer with the air on ..or climbing a 1.5 mile incline with 33" tires.

See if you can find a buddy with an infared gun (I think that they are actually cheap ..but expensive for just one use).

Man I had fun with my closing company's thermal imager ($50k new) for about a month. Did some nice energy surveys ..on just about everything. I could tell what color underwear a woman was wearing by the heat that they threw off (shameful ..I know).

(visions of Preditor II: "Want some candy?"

)

 

[brianl703]

If it's OBD-II get a scantool and watch the engine coolant temperature PID.

I just did that with my '96 Contour...the fan comes on at around 211 degrees, and in about 40 seconds (at idle) the temperature drops all the way to 195 degrees, then the fan shuts off.

This is with a 70F outdoor temp.

That's a pretty powerful fan to drop the coolant temperature 16 degrees in 40 seconds, I think.

 

[MarkC]

It is indeed a 96 with OBD II.
But it came with only idiot lights, and I couldn't stand it, so I had a temp gauge put in. I had to put it low down beneath the main instrument cluster area, in the panel I believe is usually used for extra light switches or something. It's wired directly to the sending unit, which is the one on the driver's side of the block, near the firewall.
I've been through 2 or three senders in 7 years, but the gauge always reads just a touch on either side of 190 unless it's really hot outside and I've been sitting still for a long time.
I put in a new 195F thermostat a month ago, but the gauge acts the same as always.
The reason I'm wondering is because I'm bored! and also because my exhaust pipe gets a ring of black sooty carbon stuff around the opening and it bugs me, although I've seen this on many vehicles.
I thought about engine temp, MAP, MAT sensors, O2 sensors, etc...but I have no trouble codes and the engine is running like it was new. Gas mileage is great...for a Jeep...and power is still like it always was.
I'm probably just picking at stuff that's not there because I'm bored.

 

[Gary Allan]

Hey, Mark ...most of the walking population would tell us all here to "get a life"

This makes a little more sense. The temperature sensor is reading from a different point in the engine (it should be at the thermostat housing on the bypass port). Your engine appears to be well regulated thermally.