Temp gauge dropping under acceleration

Hey guys, tried a forum search and I couldn't find anything relating to this specific issue.

I have a 97 Cherokee sport with about 295,000k on her, yesterday I changed the plugs, wires, distributor cap and rotor. Started it up and everything went fine, running like a top.

Took it to work today and noticed something strange on my way there. When I accelerate the temp gauge will drop down to the one just above 40. However when I stop at a light, after about 15 seconds it will go back to right in the middle. I've never had any issues before, always been and stayed dead center once she's warmed up.

Is it possible I've knocked a sensor loose or something while I was changing out the plugs? Any help you guys can provide would be greatly appreciated! Thanks!

Sounds like time for new Thermostat, the old one is probably sticking in the open position.

did you check your coolant level? It almost sounds like it's low.

Coolant temperature will rise when the vehicle is stopped and fall when the vehicle is moving. One reason for this is the ram-air through the radiator when you are moving, but another reason is that the water pump spins faster when you are working it at 2500 RPM than when you are idling at 750 RPM. Furthermore, the thermostat typically works its way open when you are sitting stopped at the light, since temps keep rising, and then you take off and crank up the water pump and a blast of cold coolant goes rushing into the engine.

However your temperature should not drop to 140 so yeah your thermostat is probably sticking open and ought to be replaced.

Behaving like a diesel. Is there something you haven't told us?

Last time i checked the coolant level was fine. Ill double check it tomorrow. It just seems strange for this to just start after doing a tune up after it was running fine before. I guess it could be coincidence though.

Would it be alright to drive like that till i can get a new tstat in this weekend?

Sound like it needs to burp. If the coolant level drops below the sensor, it will not register the temp of the air. This is why it's important (IMHO) to use the T-stat that seems to be only available from the dealer. The little check-ball doesn't seem like much, but due to tight packaging to put a rather tall engine into a somewhat squat body, the T-stat housing ended up being the highest point in the cooling system. Higher than the radiator cap, the traditional top spot. I've noticed through the years that when one of the Heeps had a normal T-stat installed, the temp gauge would take its time coming up from a cold start, then jump up to normal when the stat opened. When I installed the correct one (the correct way-ball up), it comes up the right way, an air bubble not keeping the coolant trapped below the sensor. Some on this board have suggested parking with the nose of the car facing up a hill, or jacked up, while it idles up to temp with the cap removed. Any or all of these tips may or may not work, no guarantees, and as always, your results may vary!

My '98 developed the EXACT same problem.

Remove the electrical connector from the temp sender on the T-stat housing, get in there and clean both connections with a small wire brush, put some dielectric grease on the connector and reassemble.

That's what did it for me about 3 months ago and it hasn't happened since. If you try it and it doesn't work then look at replacing the T-stat and/or the temp sender

Original_MudButt said:

My '98 developed the EXACT same problem.

Remove the electrical connector from the temp sender on the T-stat housing, get in there and clean both connections with a small wire brush, put some dielectric grease on the connector and reassemble.

That's what did it for me about 3 months ago and it hasn't happened since. If you try it and it doesn't work then look at replacing the T-stat and/or the temp sender

Click to expand...

This looks like what was going on. I pulled the sensor, blew it out and cleaned it up it up. Works like a charm now

Thanks guys!

Nhil90 said:

This looks like what was going on. I pulled the sensor, blew it out and cleaned it up. Works like a charm now

Thanks guys!

Click to expand...

Cha-CHING!! We have a winnah!!!arty:

I had the same problem with mine.

I knew it had nothing to do with temperature, engine heating.

It was clearly an electro-mechanical problem.

In my case the connector on the sending unit was BROKEN.

New sending unit and all is well.

Actually in my case it was sorta backwards, when I sat at idle it would drop off and under acceleration it would read.