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strangest cooling system problem

mushrat_1

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Joined
February 28, 2006
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City, State
bellingham, wa
Year, Model & Trim Level
92 XLT
Ok, so its a 1992 Explorer XLT 4.0L 5-speed w/optional tow gearing. When I bought it someone had replaced 2 of the 3 freeze plugs on the passenger side of block with rubber (crappy)ones. Dont know why. Two months or so ago one popped out and I shut it down immediately. Replaced missing plug with a brass one, threw in a little bars leak just in case a bad head gasket was causing excessive cooling system pressures and figured I would give it a more thorough going over once the weather got better.

Now, heres where it gets really weird.

Lost heat from heater a few weeks ago, thought it was no biggie, must be losing a little coolant. Coolant level was not low at all. Given that the heater core is only 6 months old, I figured it must be the bars leak. I hooked a flushing tee into the heater line and flushed the entire cooling system. The stuff coming out of my radiator neck literally looked like, well, a bowel movement. Very thick and very brown. My first thought was the bars leak, but WAY more of this stuff came out than the amount of bars leak I had put in. Waited for the water from the flush to run clear, buttoned it up and away I went. Heater was working great.

A few days later, no heat. Popped the radiator cap to check the level, and chocolate milk was all over the cap and inside the radiator neck. INSTANT PANIC!! Checked the oil, perfect. Thought it might be more bars leak residue so flushed it again. A few days later, same thing.

So, now I am in a big arguement with my boss. He says I am getting oil in the cooling system. (which is exactly what it looks like to me too) My response to that is, the oil getting in there would have to be under more pressure than the cooling system, or it would be water in the oil. In my experience, there are no pressurized oil passages next to coolant passages in modern engines. Only oil drain back/return passages, which, of course are not under pressure and could not force oil into the cooling system.

Does anyone here have the expertise to teach me I am wrong, and this indeed is the case? It sucks doing all this flushing when its only 35 deg. outside, and if it is oil getting into the water then I think I just need to do an engine swap and get it over with, but don't want to, if not necessary.

thanks for any help
 



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I had a very simular isssue (my motor is getting rebuilt at the momment), although flakes of what turned out to be rust was the problem. The coolent will have a rainbow effect if its saturated with oil. The rust is probably from and old radiator thats in desprite need of replacement.
 






Oil pressure (say 30 - 60 psi) will exceed water pressure (16 PSI approx).... SO any leak betwen the two will allow oil to enter the cooling system.

Head gaskets are a prime suspect.

Start there.
 












Ouch. Yeah, that too. And we have a vehicle that has a tendency towards cracks in the heads if overheated.

Your assumption that there are not locations where pressurized oil can cross connect into the cooling system is misplaced. There are numerous locations in the heads this could occur, and also in the head to block gaskets. I'm hoping you just have a gasket issue (which if you pull the heads will be VERY evident in the gasket, should it be the case).
 






When my sister over heated my 94 back in the day it did blow two freeze plugs on the passenger side. If the same thing happened to yours then you may have a cracked head if the previous owner ran it to long with no coolant. I would maybe mark the dipstick next time you flush it, then check it a few days later. Being a 92 you will burn some oil, but it shouldnt be much.
 






The brown mush is consistant with a bad head gasket of cracked head or on occasion a cracked block. If the cooling system is not holding pressure, it will not back flow water into the oil crankcase, and thus oil will appear normal. I drove an old Ford Flathead that way for 2 years in High School; not recommended, but not totally disabling.
 












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