ljobbins

First off sorry for the long post but want an accurate description of the problems. My car is an 88 4.0 inline 6 Manual trans 4x4 mostly stock not lifted or giant tires. Two days ago I was driving home and after 45 minutes my dummy temp light went on so I pulled over and looked at it and it didn't seem hot and nothing looked or sounded wrong but I didn't want to risk it with the light on. I let it cool for a while on the side of the freeway and when I drove again it started off not lit then lit again in 5 minutes. Repeated until I made it home. Next day my friend came over and looked at it. The more we ran it and shut it off, the more the light changed and did funky things. Sometimes the light would work on the key foreword test or the grounding test sometimes not. After a while our best guess was the sensor. We went to oreillys and got one. After a while of the new one and running it the light came on dimly but not all the way bright but the light does light up fully on the initial start up test so the light is good. Decided it wasn't overheating so I ran it to work this morning. Then on the way to work the light was dim then bright for 15 or so seconds then back to dim. Didn't trust it so I took it the radiator and cooling specialists and they said the radiator was shot and couldn't be fixed. Got a new one and flushed and filled with new coolant. Also replaced the water pump thermostat and lower radiator hose a month and a half ago. On the way home today the light came on dim again and it's only a 15 minute freeway drive. I want to take it back to the shop to have them check it again to see if they can find anything else wrong, but I wanted to see if anyone here could think of anything. I am also going to get a multimeter from my friend tomorrow to test the wires, but in any case I don't think the light should be getting any power unless the sensor is sensing something but at this point I don't what is going wrong. I would also like to know if anyone has any info on installing a temp gauge because I would rather have a gauge then a stupid light. Any help would be great.

Bustedback

You have to be sure that you burp the cooling system to get the air out on a closed system. Get a temp gun and confirm the actual temp when the light comes on. You may just have the sensor wire grounding out someplace. Does the light still come on with the sensor unplugged?

ljobbins

The shop said they ran the coolant through the whole system but i know there could be a couple little pockets of air in there but they would just work themselves out right? Also the light does not come on unplugged and when tested it shines bright but when plugged in and running it is dim like the sensor is giving a tiny bit of a ground to close the circuit but not enough to light up strong which is weird because I thought it was a on off light not a dim to bright light. Thanks for helping.

Bustedback

I wonder if the parts store sold you a sender for a gauge instead of for a light.

ljobbins

I asked them and he said no and it's just a simple sensor. It is two different metals and as it heats up they touch and close the circuit. It is just a stem on top that the wire for the light plugs into. Sensor stem to plug with wire to fuse to light. I do have lifetime warranty on the sensor so I can swap it out at no cost and try a another new one but it's a pain because I spill a good amount of fluid during the switch.

Bustedback

He gave some wrong information, there are different senders for a gauge and a light. The sensor for the gauge is a variable resistance sender, the sender for the light is more of an on/off switch. I think you have the wrong sender.

ljobbins

Ok I'll check it out

cruiser54

Or the engine is seeking ground to the chassis through the sender?

You have an 88.

Click on the link in my signature and go through and perform posts 1 through 5 without taking any shortcuts.

Post 18 may also apply.

Always a good idea to replace the coolant bottle cap with a 703-1396 from Napa.

Firestorm500

If you have "air pockets in the system" they will not work their way out of a closed cooling system, such as your Jeep has.

Take the cap off the bottle when cold. Warm to operating temperature, with the heater enabled too. Then run it at high idle, about 1500 RPM, for about 5 minutes. Observe the coolant swirling through the bottle. When the air bubbles stop, you have successfully gotten them out.

Air pockets can and do stop the coolant from flowing.