ianD

Sorry if this has been covered before, I searched for an hour and couldn't find anything like this. 1990 pickup, just rebuilt 22RE engine top and bottom end. I replaced most everything in the cooling system, water pump, radiator, new hoses, thermostat, and I flushed the heater core while everything was out. Before the rebuild the temperature gauge stayed solid about 1/3 of the way up, after the rebuild when warming up the gauge will go up at least halfway, sometimes more but after about a minute settles back down to the 1/3 area. I suspected the thermostat (190 degree) and pulled it out and did the hot water test and it didn't start opening till about 220 degrees. I tested the old one (180 degree) and it opened at the right temp so I put it back in but still had the same problem. I tried bleeding the air several times parked on a steep hill with the front end up, at first I could hear air gurgling in the heater core but after several tries I can't hear it anymore so I think I got it all. The heat works fine and I visually checked to make sure the valve by the firewall was opening all the way and both the inlet and return hoses are hot so coolant is flowing. I was always driving with the heat on but the other day I tried turning it off while warming up, the temp gauge went up to about 1/4 of the way and stays there rock solid but when I turn the heat on it creeps up a little bit. I've tried keeping the heat off while warming up several times now and the temp gauge never goes above 1/4 of the way. I'm completely stumped on this, could it be the temp gauge just acting funky? Any input is greatly appreciated, thanks.

Co_94_PU

iTrader: (-1)

Between about one and three quarters is perfectly acceptable...

The gauge is a resistor based unit, that is it's a resistance based sensor. They are susceptible to fluctuation based on minor resistance changes due to plug vibration, voltage change and heat along with variation in construction.. ie not very accurate alone much less when compared to another random sample.

Due to where the gauge sensors are located they see more flow when the heater valve is opened, heater line is directly below the sensor in the middle of a 2xR based intake..

Ps, unless you live below sea level you need to recalibrate that thermometer, water boils at ~212..

ianD

Ok Just seemed odd, I don't remember it doing that before but I didn't pay as much attention to the gauge before I rebuilt the engine. One of these days I'll put in a more accurate temperature gauge. I may have been wrong about that 220 degrees, I did the test a month or so ago and forgot exactly what temperature it opened, it was above 200 though, water was starting to get a little bubbly

Co_94_PU

iTrader: (-1)

Attribute it to slight variations in manufacturing old vs new sensor, that covers differing gauge readings. Old scaled over sensors , the deposit acts as a thermal barrier (like a sweater, lol)..

Just keep an eye on it, mostly for extreme changes from the new norm.

Also remember air pockets when lodged on a sensor will either drop the needle or peg it out, usually they drop to zero.