93 - Slightly overheating, then cooling off.

[scrivyscriv]

I noticed my temp gage going to the far range of NORMAL and then slowly returning to its regular spot about a month ago, so I changed the thermostat. Replaced it with an AutoZone Valucraft $4.00 part, and it seemed okay for a few days, but then started acting up again.

It warms up, sits on the 'N' or 'O' of NORMAL, then will climb to the far end - but not as far as it did before I changed the thermostat - and quickly return back to the 'N' or 'O' it lives on. The gage most often, but not always, rises when I'm not moving, and will return as soon as I rev the engine.

Heat was blowing hot until I changed the thermostat, now it blows a mediocre warm.

Coolant is about 70/30 antifreeze/water.
Squeezed the upper radiator hose with the engine running and felt pressure build up.

I've seen similar threads but nothing that describes my Explorer.

Temp sensor?
Fan clutch?
Thanks for any help.

 

[boggs1227]

flushed it latelly ? did you get all the air out of the system ? any scaleing on the inside of the radiator?

 

[rocco123]

Been working this same problem for over a year. Temp always fluctuates. About 2 months ago I replaced the thermostat when changing my radiator (due to a rad leak). Problem still there. Just replaced my intake maniflold gasket due to gasket failure (replaced thermostat with a Stant brand). Cleaned & flushed the system with garden hose flush kit. Still fluctuates temp. Not just an indication, the temp gets cooler & warmer coinciding with indication.

 

[scrivyscriv]

Scott, you caught me! I haven't flushed in a two years, LOL. I'll grab a flush kit and update on how effective it is for this problem. And yes, there is scale inside my system - saw it in the thermo neck when I was changing the thermo, and couldn't get that crap off for anything.

 

[dewgod]

I had the same problem on my 94 and found a hair line crack in the top of the radiator. It couldn't keep pressure because of the leak, but evertime I stoped the vehicle I could see no antifreeze leak (cause it was on top). Didn't always over heat, just when it had to "work", like climbing hills etc.

 

[boggs1227]

well 'flush' is a acid based chemical ...it's designed to eat corrosion and break it up ...if you got a rad with a LOT scaleing ( corrosion ) then if it's bad enough ( beacuse now the whole structure is weak ) you "could" eat a hole in the radiator and kill it . a pic would help .

when i bought my explorer last year i flushed the system with just plain water ( no flush agent) i let it run for about 10 minutes and i had a LOT of brown rusty water and crud float out of mine
(used the prestone flush adapter kit ) ....plus my truck had sat doa for 3 years in the woods so i think that if another year or two had gone by i would most likelly had to buy a new rad and heater core ...i think i saved it in the nick'of time .

 

[Hossexplorer]

I was about to post a new thread on this same exact issue! I changed the thermostat and now the temp fluctuates from "N" to "A". Ive read other threads about burping the system and i have let it get to normal range and filled it constantly while the radiator cap is off. And I have filled the overflow tank and drove for over 20 miles but it hasnt burped itself. Temp still is fluctuating. Also there is no scaleing and coolant is clean looking. -What are other ways to burp? Or am I missing something?

 

[boggs1227]

the way i 'burp" the coolant system is while cold and engine off i take the cap off and squeeze the upper rad hose and watch the coolant go down ..once it's down i do that a couple of moretimes till finally the coolant is about 1-2 inchs down then i add more coolant to fill it back up .couple of times doing this will burp all the air out .

...works for me at least

btw:: whats with the sudden rush of coolant issues this week...anyways ?!?

 

[fixxxer]

Has anyone tested or replaced the radiator cap? They do go bad. If that doesn't do it, pressure test the system. You can rent the tool at most auto-parts places.

 

[scrivyscriv]

Scott, I backflushed my system and am currently cycling a flush chemical through it for another three or so hours of engine time. I'll tell you though immediately after backflushing, my temps leveled out and my heater started kicking out about 30% more heat.

Coolant was mostly greenish, but the stuff at the bottom of the radiator coming from the **** was a rusty brown. Didn't see much as far as suspended particles or anything like that, though... but I'm sure I will once I flush this current chemical out

 

[boggs1227]

thats great ....glad to help out ...just make sure that when you put in the coolant mix to use distilled water and not tap ....that will kill it in a heart beat .

good luck !

 

[Willard]

I have had the same problem for a couple years. Radiator is new (for other reasons), t-stat is new, and cap is new. Now leaks, doesn't really use any coolant. One thing it does do though is the coolant overflow reservoir overflows all the time.

I cannot confirm it, but I'm thinking the reason behind this is a possible very small crack in the head gasket, causing the system to get pressurized from cylinder compression. This, in turn, pushes some coolant out, and also tends to turn the coolant a kind of brown color from some of the crap getting pushed into it. There is no coolant in the oil, and no oil in the coolant.

So that is another thing to consider, especially if it looks like coolant has overflowed from the overflow reservoir.

 

[scrivyscriv]

Jesse,
Man, what a frustrating problem that sounds like!
It would be really interesting on down the road to find out what the source of that problem is... I'm not sure a crack in the gasket that's small enough to not let coolant or oil flow is going to be big enough to allow the kind of pressure out that you're talking about though!
On that theory, however, have you checked compression on your cylinders? I know it would be hard to tell, especially if you have a lot of miles on your motor, but worth a shot nonetheless.

 

[Willard]

No, I have never checked compression to see if that was possibly the issue. The thing runs smooth and strong so I really don't care.

The gasket being the issue was something I gathered from reading on this site, I believe 410Fortune first said it, and it does make sense to me. If you think about the kind of compression a cylinder has it is plausible, especially with 215k+ on the motor. I think it would be a crack straight from one of the water jackets over to the cylinder, so oil would not be able to get mixed in there. There's also a small chance it could be a extremely small crack in the head, since it's been overheated more than once, but I would think something such as that would be much worse.

 

[scrivyscriv]

Just as a follow up for future thread searchers - the problem with my temp gauge was because the heater core was partially blocked. I changed it because it had a pinhole leak and was sending smoke out the vents, and from then on my temp gauge has stayed rock steady with no problems at all.

It's an easy fix, too, one that a thread search should pull up many 'how to's' for. My heater core was under lifetime warranty from O'Reilly's and they replaced it no questions asked.

 

[Robrt32]

Mine does this too AND when I got the truck the water was routed back to the block.. The plastic valve had cracked and the previous owner was too cheap to spend 20 bucks.. He had ran it a year or more with the heater core nipples wide open.... I had a MEAN heater last winter though... I ALSO don't remember the temp gauge fluctuating BEFORE I put that plastic valve back in.... interesting... I'm gonna check this out... THANKS MAN

 

[doonze]

So the new heater core solved the problem? I'm going through the exact same thing myself. Course when I changed the thermostat it took a few days for issue to come back, so I'll wait to see if your issue also stays fixed. I don't really see why a blocked heater core would cause the temp to rise for a few moments then drop back down quickly. Unless it's just that not enough water is flowing on the block side of the system to allow the thermostat time to open. Hmmmmm... Course I also have a "running hot (around A) on long freeway trips" issue I'm also dealing with, so this issue has been put on a back burner while I try and figure the bigger issue out.

 

[scrivyscriv]

I changed the heater core about two months ago actually. I just never got around to updating this post since it was already several months old... I don't know why exactly a plugged heater core would cause it. Let me know when you find out more about your situation. I'd like to be 100% positive that it's the heater core, for future reference.

I've heard of X owners with heater problems just capping off the core and putting a connector between the two heater core hoses, and if that doesn't cause any problems, I don't see how a plugged core would.

The only other maintenance related to this problem has been a chemical flush and t-stat replacement, both before the core replacement. The t-stat helped the problem for a day or two, but then it went back to running hot and cycling.