Overheating Issues...

[Warrof]

Hey guys and gals,

So my wife and I bought this 1994 Ford Explorer Limited back in April 2019, at the time we needed a bigger vehicle for our expanding family. It had been sitting for a while, but it had low miles and the v6 4.0. And my Mustang isn't a family vehicle neither was her Suzuki Samurai.

Within a month we had to replace the Water Pump, Thermostat, Radiator Cap, and a couple of the smaller hoses. Also flushed the system with the Prestone cleaning kit, lots of crud came out. Pretty sure the family that bought it off the lot in '94 never did any maintenance except for oil changes.

That fixed it for a while, ran quite cool for about a week. Then more stuff happened. Ended up replacing the Radiator and fan(was cracked). That fixed it for a while, again. Due to stupidity, my dad and I forgot to run the lower hose correctly, the belt rubbed a hole in it.

At this point I wanna shoot the blasted car, so my in-laws car-napped the Explorer and took it to the local mechanic (good guy, does good work). Considering my wife was due to have our first kid, I didn't really care about the car. Mechanic replaced all the hoses, heater core, and the valve that runs to the heater core. Been running really great since! 1 month and 3 weeks...

About 2-3 weeks ago the car started overheating while idling with the AC on... with my experience I knew that wasn't unusual so we started running without the AC unless we were on the road.

Last night, she really overheated bad. Boiled out everything in the reservoir, and a fair bit out of the radiator.

Just to summarize I've replaced, fixed or tested:
Water pump, radiator cap twice, thermostat, radiator, fan blades, all hoses and clamps, tested for combustibles in coolant(negative twice), flushed a few times, cleaned with Prestone Cleaning Kit, heater core, heater core line valve... I think that's everything.

Next I'm gonna replace the fan clutch(did not replace that) and see what kind of crud is in between the radiator and the AC evaporator (or whatever it's called).

Does anyone have any further advise?
Proabably gonna go through this guide as well.

How To: Doonze's Ultimate Radiator Flush!

 

[Josh P]

I've had mixed results with the 4.0L overheating. One motor had no issues and another motor cracked a head causing coolant to go into the exhaust. I'd upgrade the fan clutch to a severe duty found on the later 4.0L ohv and sohc engines.

 

[Kesp4.0]

Are you certain that it boiled out that coolant because it overheated and not that it started to overheat because it was low on that coolant to begin with? There may be a leak somewhere that caused a reduction in the coolant level to where the car begins to overheat as a result.
That happened once in my 93. It was already low on coolant and I neglected to check it for a while. One day I'm trying to drive home but there was heavy traffic and my car started to overheat. I never let it get too hot and was able to limp it home after pulling over and letting it cool every few minutes. Come to find out there was barely any coolant in there.

 

[Warrof]

Are you certain that it boiled out that coolant because it overheated and not that it started to overheat because it was low on that coolant to begin with? There may be a leak somewhere that caused a reduction in the coolant level to where the car begins to overheat as a result.
That happened once in my 93. It was already low on coolant and I neglected to check it for a while. One day I'm trying to drive home but there was heavy traffic and my car started to overheat. I never let it get too hot and was able to limp it home after pulling over and letting it cool every few minutes. Come to find out there was barely any coolant in there.

I've gotten in the habit of checking the radiator coolant level before anyone drive it for the first time everyday, also make sure the reservoir is topped off. The radiator was full overnight, the reservoir was a little low (but it always is for whatever reason) that morning. Filled it the 1 cm back up to cool fill line. Also, the only place that ever looks wet, overnight or otherwise, is around the reservoir lid.

I've had mixed results with the 4.0L overheating. One motor had no issues and another motor cracked a head causing coolant to go into the exhaust. I'd upgrade the fan clutch to a severe duty found on the later 4.0L ohv and sohc engines.

Such as this? Advance Auto Parts - Down for Maintenance Or is there a better brand? (this is the only one that comes up on a google search that I've found) Dunno why the link says down for maintenance... links to the correct page though.

 

[Josh P]

6L5Z 8A616 BA is the ford part number and the napa part number is TEM 273387. Came standard on the 98-11 4.0L. I like that fan clutch cause when it fails, it fails locked up so you won't overheat. I've used that fan clutch on my 91 4.0L aerostar van. My 99 Jeep grand cherokee had an overheating problem and that fan clutch fit the 4.0L inline 6 engine too with a gmc 11 blade fan attached to it.

 

[gmanpaint]

Do a boil test on the t-stat to make sure it's good.

Burp the system for air, until hot air comes out of the vents at idle. Your new core might have air trapped in it.

What PSI rad cap are you running? Boil over points matter.

Check the pump hoses when hot. Hard or soft? Collapsed or expanded?

 

[Warrof]

Do a boil test on the t-stat to make sure it's good.

Burp the system for air, until hot air comes out of the vents at idle. Your new core might have air trapped in it.

What PSI rad cap are you running? Boil over points matter.

Check the pump hoses when hot. Hard or soft? Collapsed or expanded?

Not sure how to do a boil test... And the cooling system is currently draining, but very slowly. Need to do a serious cleaning.

The new heater core produces plenty of heat, even at an idle. Though I do not know if the mechanic burped the system, I imagine that he did. Really good guy and a solid mechanic.

Was originally running a 16 psi cap, but it didn't seat right (the original and the replacement). Was always blowing coolant out of it and never allowed for coolant to be pulled in from the reservoir. My dad pulled the 15 psi cap off of his Chevy 1 ton pickup... That cap works beautifully.

The hoses are well pressurized while running hot, and the radiator is always full, minus the recent overheat.

 

[Warrof]

Update: During the back flush I couldn't get the drain hole to drain at all, well very little. Decided to pull the radiator out and blow it out with water. Got tons of debris to come out. The drain hole now drains fluid very easily... Tomorrow I'm gonna pull the water pump and thermostat off and flush the engine block thoroughly, then do a proper flush with Prestone Flush.

Hoping that between that and the new Fan clutch the vehicle will stay much cooler.

Edit: I did cover the transmission coolant holes before spraying.

 

[Warrof]

Update: The flush is about 1/2 way done, 3 out of the 6 hours. The water level dropped a fair bit the first day, but today it only dropped a little bit. (Was frustrated and didn't drive it for a few days.)

I will admit that I am getting fairly fed up with this machine. I'm giving it till after the second flush treatment... If we are still having issues I am going to be seriously looking for a different vehicle

 

[gmanpaint]

It can be hard to burp the air out sometimes. Its good to have the front of the rig, higher than the rear when doing it. If you have to, Jack up the front.

One method..
Cap halfway on, heater on high, go ahead and turn the blower all the way up, and let it idle for 10 mins. Close the cap, shut it off.

A boil test is simply putting the stat in a pot of water, and heat the water up. Watch the stat, as the temps rise. If you can see it open before the water begins to boil, its good.

 

[MrQ]

My brother dealt with an issue like this. Completely rebuilt the whole cooling system, added electric fans, heavy duty fan clutch, bigger radiator, bled and flushed the system multiple times, the works. But every time he turned the A/C on the temp climbed. Turned out to be a small head gasket leak. Within a month after diagnosing it, his oil turned to chocolate milk. Not saying this is the issue, but it's quite possible.

If you do wind up going that route, replacing the head gaskets are not too bad on the OHV. It's a little tight on the passenger head, but still doable. Just keep everything in order that comes off the heads and it should be fine.