I spent the past 2 days replacing the intake manifold gaskets due to leakage. Well, finally got it up and running. I double and triple checked everything. I let the vehicle run for about 10 minutes or so and the temperature gauge stayed on the first mark the entire time. I wasn't anywhere near the coolant temperature sensor or its wiring when doing everything. Is my 4.3 going to overheat?

The ONLY thing I can think of is that I think the coolant temperature sensor is in the driver side head, so maybe it won't get a reading until the thermostat opens? This just makes me nervous since there isn't any coolant in my block, how long is it going to take to get a reading? OEM temperature thermostat, btw.

Gauge was working just fine before the intake manifold gasket replacement.

For the first 5-6 minutes I ran without the cap on but I got nervous and shut it off...silly me wasn't thinking and coolant started coming out of the radiator so I put the cap back on and tried running it another 5 minutes or so like that.

Edit: also, I noticed that the thermostat housing was VERY hot after that time. The upper radiator hose was cold, and the lower radiator hose was just barely warm.

98 jimmy, 4wd, 4.3

Edit: problem solved, ECT sensor unplugged.

 

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The temp sensors dont have anything to do with thermostat or coolant flow. Just reports coolant temp.

thermostat controls coolant flow, if there's enough in the system.
Didnt happen to install thermostat upside down, did you?

The gauge sensor has one wire. The ECT sensor two.
Ground the one wire connector and gauge will go to 'hot'. If it does that and gauge still doesnt work when reconnected, bad sensor.

 

Thermostat is fine. Radiator as full as it will let me until thermostat opens. I'm just saying...temp gauge not picking anything up. I'm running the truck trying to get thermostat to open so I can bleed cooling system.

 

What are you working with? Information to help you depends on the year of the vehicle. This information should be provided in the first sentence of a post requesting help.

How are you so sure that the thermostat is not the problem?

 

98 Jimmy 4.3. thermostat worked before I did intake gaskets.

Just ran it for 20 minutes with cap off. Coolant level in radiator went down very slightly, top hose got a little hotter but still nothing registering on temperature gauge. Thermostat was known good & tested before I changed the intake gaskets. :/

Edit: oh and my heat works :S

 

Edited
If heater works usually means it isnt air locked

Which of your sensors is one wire and which is two?
If the one wire is in the head then I'm pretty sure it has hot coolant around it. If it's up top and heater works and therm housing is hot then somehow it got bad. Like I said before, ground that wire to see if it's sensor or the wire.

 

It is either the thermostat or the temperature sensor. Since you didn't really do anything to either of them during the repair, something went wrong somewhere... Heat doesn't require that much of a differential in temperature to "work" and it bypasses the thermostat so I would call that observation somewhat moot. Do you have any means of verifying the temperature at the thermostat? Infrared thermometer would work great in this case.

If I am reading your description of the problem correctly, you are stating that you let it run for 20 minutes and the upper hose still has not gotten hot... This doesn't make any sense at all and points directly at the thermostat if this is the case.

On an early '98, there may be two sensors. If there are two, there will be one near the thermostat housing mounted below the thermostat in the lower intake and another in the driver side cylinder head. PF already described both of them. If there is only one sensor, then it will be in the driver side cylinder head between cylinders 3 & 5.

And please edit your post to include additional information. Posting consecutively is prohibited by the rules of the forum.

 

I'm going to double check the wiring, losing daylight though :S I think I saw a plug underneath the thermostat housing (in the lower intake) -- so I'm guessing I only have the one sensor that reports to the gauge and ECM?

Edit: the upper hose IS getting hot. I'm going to assume that it's the wiring from the sensor and go from there. I do have a check engine light now, so maybe it points to the ECT sensor anyway...just too scared to drive it somewhere and see.

 

If you only have one sensor, it should be a multi-wire sensor located in the driver side cylinder head.

Could you clarify some points? After it runs for 20 minutes, is the upper radiator hose still cool?

 

Problem solved. I looked @ the coolant temp sensor earlier but didn't realize it was unplugged. Part of the plastic where the wiring harness plugs in is broken so the two leads are sticking out. If I hit a big enough bump it'll pop right off again. "Plugged" it in, gauge works. Running at 195 on the dot! Good to know this forum is so ready to support its members.

Drove to AutoZone, checked computer...just one code, coolant temperature sensor voltage too high. Reset it, now I'm good to go!