today i was driving home in my recent purchase, a 1995 ranger xlt with the 4.0 v6 in it. i was glancing at the gauges to make sure everything was normal when i noticed the coolant temp gauge acting odd. it would slowly make its way up to about halfway up on the gauge, then go back down to 1/4 of the way up. then it would go back up to 1/2, then back down to 1/4. it kept doing this the whole ride home, which was about 20 miles of 60mph highway cruising. i didn't worry about it too much because it wasn't overheating. i got home, checked the radiator, it was full. the coolant tank was low, so i added some coolant. the oil is fine, no coolant in it. i let the truck idle back up to temp and the coolant temp still fluctuated, but not as much. the check engine light is on, and the previous owner told me its from what he thinks in the egr system. i have not been able to pull a code from it as of yet. i'm not new to cars, just to rangers, so i'm hoping someone can point me in the right direction. thanks in advance!

 

I was gonna say air pocket but i dunno if its full even though it still could be. Thermostat could be sticking open. Could also be the sending unit for the coolant temp is bad.

Also does it only fluctuate while driving or while at idle as well??

 

I was leaning towards an air pocket as well. I'm gonna flush all the fluids anyway. I'll put a new temp sensor in and change out the therm too.

 

My CEL is on cause of the EGR. it seems to be common.

My family had a buick that did this. Turns out the head gasket had blown. Even though there were no real signs of breakage (Coolant in the Oil, etc...)

Not saying this is what the problem is, buts its a possibility

 

The buick was doing the temp fluctuating? I would think that it would at least overheat if the hg was bad. The exhaust doesn't smell like it's burning coolant or anything either.

 

Hey bud I have an 04 with 35k that the thermostat was shot, it did the same thing. Replace that sucker! Cheap fix

 

I would jack the front of that truck up, let it run w/out the rad cap and bleed it out real good. Air pockets can do this, however i would also find the wire that goes to the temp sender and ground that wire out while watching hte temp gauge. Make sure it's not getting stuck w/in it's sweep. Had a bad temp gauge and the thing acted like a "dead spot" somewhere in the sweep. It would go from 1/3 to like 3/4 too hot.

 

THe typical ohv tstat starts to die the truck does not warm up as the tstat opens early. truck works fine in the summer but has no heat in the summer. I replace mine every two years for this reason.

If someone has used a crappy tstat they tend to not maintain the desired temp and can bounce around. It will be more noticeable as it get colder outside.


So with that being sad tstat and a coolant flush/fill should take car of the problem. If it comes back you most likely have a small leak in a hose somewhere letting in air. Plus it will lose coolant.

 

Update...had a local shop plug in a scanner...temps are fine, the gauge just fluctuates on it's own. Now I'm just keeping my fingers crossed.

 

Bare minimum I would do is pull the radiator cap when its cold and let it warm up for 15 or so minutes. This will purge a air bubble if you have one. Top off if it needs it with premixed coolant.

Then cross your fingers.


IMHO, a thermostat is a regular maintenance item. Which should be down with a coolant flush every 2-3 years.

 

I did change the thermostat and ran it with the radiator cap off.