Cooling System issue

[sroth004]

Hello all, having a cooling system issue or issues on my '94 Explorer with 82k miles that I'd like to run past the group. I am the second owner having purchased it a few years ago with a bit over 60k miles from the daughter of the original owner. I sat indoor for a couple of years prior to my purchase. Sorry in advance for the long story.

Last Spring I notice the coolant in both the radiator and overflow tank had turned very dark, almost "greyish" and had a odd consistency. I drained/flushed/refilled/bled the coolant and within a few hundred miles the new coolant started to look the same greyish. Brought the car to a garage that has done quite a bit of work on this vehicle including head gaskets due to external coolant leaking at the rear of both cylinder banks. The shop flushed the system again and also replaced the thermostat and temp gauge sensor with the Motorcraft units I provided (the correct 197 or 198 degree thermostat). After the work was completed the X exhibited wide swings of the temp gauge as it was driven, swinging as far right as just below the line on the hot side of the gauge, with the coolant again becoming greyish fairly quickly. I sent coolant and oil samples to for analysis, with testing indicating no oil in the coolant and no coolant in the oil. The X was stored indoors for the Summer and when I pulled it out to get ready for Winter use attempted to purge the air in the system that was easily felt in the top radiator hose consistent with the swinging of the temp gauge to the hot side. Purging the air helped but did not eliminate the gauge swing so I assumed I was no successful at purging all of the air.

I brought the truck back to the shop that completed the last flush. They flushed the system again, with feedback was that they felt there was stop leak in the system at some point based on there being small black solid debris in the flushed coolant and recommended replacement of the radiator, water pump, etc...I let them replace the radiator, water pump, thermostat, etc...but not the heater core (no way was I removing the dash) along with another full flush. I asked and they did not recommend replacing hoses, which I believe may be original. The swinging of the temp gauge is much improved but not resolved (I have not checked for air in the system yet) however the coolant has again turned dark.

At this point I am stumped and definitely not going back to the same shop. I have not sent samples of this oil and coolant for testing yet and have not removed the valve covers or otherwise looked for cracked heads. Of note, I do not believe the engine has overheated as the gauge swinging never sat toward the right for more than a second or two and is tied to air in the top hose where the temp sensors reside.

Any thoughts or suggestions on potential next steps would be appreciated.

Thanks

Steve R.

 

[bwryan]

Can't speak to the grey-ing of the coolant, but just wanted to point out that replacing the heater core on these is amazingly easy, just remove the cover in the passenger footwell and it's right there. I've had other vehicles where it was a nightmare (looking at you, Acura), but on my '94 it was a delight. I almost did it twice, it was so easy. :-D

Easiest ways I know to check for evidence of cracked heads are looking for steam at the exhaust and looking for whiteish gunk on the under side of the oil filler cap. Re. burping the system, that really is important because if there's air and not coolant at the thermostat, it won't work right.

Good luck!

Brian

 

[massacre]

+1 on the ease of heater core replacement on these. My early fox body (non AC) is just as easy.
But a fox body with AC is a complete nightmare.
When i had swinging coolant temp, it ended up being heads cracked between the valves.

 

[sroth004]

Thanks Gents, much appreciated. Didn't realize the heater core was so easy, guess I should have looked in the shop manual, though I doubt that's the cause. I'll watch for other feedback and will update the group with an outcome.

 

[410Fortune]

Likely still some stop leak in the system it may take a few
More
Flushes to get it all out. Somebody must have used the crappy bars leaks in this rig, that stuff settles in the low spots and can be a pita to get it all out

If you don’t have any loss of coolant and the samples Came back neg for oil then i bet you’re just fine.

You may consider a new fan clutch or at least inspect the one you have, a stuck fan clutch can cause odd heating issues and wild Fluctuations of the temp gauge. I may also suggest that the temp swings are normal? The factory gauge is not very accurate
You will see 200-205 degree water temp at the dash sensor before the thermostat opens and then temps will drop to 185-190 and slowly climb back up, this usually results in the needle moving slightly but still in the “normal” Operating range

Any trapped air behind the thermostat will result in wild fluctuations of the stock gauge as it is actually reading a pocket of hot air trapped and not coolant. Raising the front of the truck as much as possible while running can help burp all the air.
The thermostat should also be installed w the weep hole in the upright position. Make sure the overflow tank is not plugged with the bars leaks.
A good drain, Clean and flush of the overflow bottle should be part of a good flush, also the overflow tube must be free and no blockage.
Radiator pressure cap should be 16# factory and should be tested or at least cleaned and a visual inspection of the seal and spring and mating surface at top of the radiator. If the truck had prior coolant leaks it is quite possible a lower psi radiator cap was installed like a 13# or lower, factory motorcraft caps are best, of course

Any debris or bent fins of the ac condenser can cause airflow issues to your radiator. A visual inspection should have been part of the radiator replacement.

Your 94 should have a dual core radiator and possibly a built in trans cooler in the radiator. You may consider bypassing the radiator trans cooler and run an additional or larger aux cooler. Info on this can be found with a search of the forum, we have discussed this in great length. If the internal trans cooler fails you will get atf in your coolant and coolant in your trans, which will destroy the trans.

The grey color indicates bars leaks was used however, not red trans fluid and not brown (milkshake) oil

For peace of mind you could disable the factory coolant gauge and install an aftermarket mechanical coolant gauge, just for testing and then go back to the stock gauge later, or run a “tee” and hook them both up

An infrared thermometer can be fun to see how the cooling system is working, take readings near the upper and lower radiator hoses and also in front of and behind the thermostat housing can give you an idea of how things are working

 

[sroth004]

Thank you 410, very helpful, much appreciated. Radiator cap is original, I have ordered a new Motorcraft OE 16lb (RS-90). I provided the Motorcraft RT-1161 thermostat (OE, 197 degree) in the Spring, shop indicated they used a new OE again a couple of weeks ago but its not listed as such on the receipt. I do need to confirm they installed a dual core radiator, also not specifically listed on the receipt. I will pursue all suggestions over the next week or so and report back. Thanks again.