Temp gauge rises, then goes back down to C while driving

[oneway]

'90 4x4 BII

so I searched a lot on here and found a bunch of "what-if" but very helpful scenerios and now i'm trying to firgure out the best place to start.

my engine temp gauge doesn't even get to the middle of the world "NORMAL" before it goes back down to C on its own while driving. It doesn't rise on its own while in park and idling....warming up in the morning. I only know the engine is warm because the idle RPM's drop as the engine warms up.

through searching the site, I found out that it could be the temp sensor or the sending unit??? but none of those suggestions were for this specific model vehicle....are they in the same location on the 88's - 90's?

Also - could it be my thermostat is closing on it's own or malfunctioning? I know on motorcycles, you can start the bike with the cap off the radiator and watch the fluid start to bubble and that means your thermostat is opening and functioning...can the same be done with these trucks? If so - my thinking is, if the fluid doesn't bubble - then it's a thermostat problem.

I don't think it's the gauge itself because the needle does move.

where would you start? Would you drive it? thanks

[joeyy]

I'm not an expert by any means of the imagination but when my Bii was having heating problems, I replaced my thermostat. Its quick, easy, cheap, and give you piece of mind that at least its not the thermostat. It seemed to help my problem, but we have different problems. Mine truck would come very close to over heating. I thought I would share that with you. Hope it helps!

[oneway]

yes...a thermostat that doesn't work will cause the engine to overheat.....so will bad head gaskets....water pump etc etc

but i am seeing no signs of over heating or running to high of a temp. But saying that only goes so far because the needle drops back down after a while

they are very cheap...$15 on jcwhitney.com and from what i understand, installation is easy as well.

I'll see if others chime in and suggest replacing the thermostat - then i'll start there.

thanks!!

[bronco_lou]

Sounds to me like the sending unit is bad or maybe a ground issue, tyr to replace the sending unit first and see if that cures the problem.
Louis

[oneway]

thanks. I'll try to locate the sending unit and see how much a new one is.

any websites recommended to purchase one from?

[oneway]

here is some info that others may find helpful


PROBLEM:
the car idles fine at warm up - starts with no problems. The temp gauge will not work as the engine warms up - but as I drive, it will rise slightly and then fall back to C. I see no signs of over heating. What could be causing this? Where is the thermostat and sending unit and temp sensor? I don't think it's the gauge itself because the needle does move. Thanks

ANSWER:
Hello, Follow the upper radiator hose to where it connects to the engine. The thermostat is under the housing bolted to the engine that the hose connects to.

Look in that same area for the temp gage sending unit.

If the thermostat is stuck open the engine will be slow to warm up and the gage will behave as you have described.

Roger"

IS THE TRUCK OK TO DRIVE UNTIL THIS ISSUE IS FIXED?

ANSWER:
I believe it is safe to drive. If you need the heater you may find it has poor performance especially at highway speeds.

Roger"

[scotty boi]

i have a bronco 2 and it was having the same problem but i came to find out the guy who had it b4 me put a aftermarket thermastat that opened up at a lower temperature which in turns keeps the vehicle alot cooler with all the fluids circulating..
when i first got mine and it was doing that i that something was going on to because of the mad heat it was pushing out but was staying so cool at the same time..
but good luck with yours hopefully it was as simple as mine

[oneway]

pushing mad heat from the vents on the inside?

thanks for that info, because that is what mine does when I turn on the heat. I turned it off thinking that would cause the needle to rise some - but it didn't. I bought an OEM thermostat - but thanks for your info - i'll have to check that out when I go to replace it.

[scotty boi]

yea it pushed out mad heat from the vents n everything but mine has never had no problems with it overheating

[scotty boi]

maybe the new thermostat is junk too...try boiling it in water and see if it opens up and if it does then try buying 1 that opens up at a lower tempature and if that dont work then try the waterpump