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post #1 of (permalink) Old 10-11-1999, 12:36 AM
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Problem w/Coolant system - Head Gaskets?

1992 FS Bronco 5.0V8 XLT

The story I am describing might sound a little confusing but please bear with me. I was driving down the highway for about 40 minutes going maybe 70 MPH. Immediately after I parked my Bronco at my residence, I heard water boiling from underneath the hood. (As I reach to pop my hood, I checked the temperature gauge and it read normal) Upon inspection, I noticed that the coolant reservoir was completely empty but was quickly filling back up with boiling coolant rising from the drainage pipe on the bottom. In a matter of seconds, the coolant filled the volume of the reservoir tank and began boiling over the top. I popped off the coolant reservoir cap just in time to try and reduce the pressure. It boiled over the top for several minutes and caused quite a mess. It was ten minutes before the steam stopped and the coolant settled. During this whole period, the temperature gauge still read normal.

I noticed that the color of the coolant was a dark brown rather than the rich green color I am used to. I had just flushed the radiator approximately one month ago. Two weeks before today's incident, I noticed that the coolant obtained a slight brown tint but was still green overall.

Approximately two months ago or 1,200 miles before this occurred, I had just gotten both heads replaced on the engine. The improvement was significant but since then, I have not noticed any negative side affects with the engine.

My feelings on this is it could be either a plugged up radiator but I am leaning more toward a bad head gasket. Are my speculations right? Could it be something else? Could the brown color in the coolant be engine oil? I recently replaced my engine oil four weeks ago. When the coolant boiled over today, it was in the evening and hard for me to get a dip stick reading. The shop that replaced my heads guaranteed the work for 12 months/12,000 miles. The driving I did this Sunday was the probably the most I have done in a long long time.


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post #2 of (permalink) Old 10-11-1999, 09:23 AM
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Re: Problem w/Coolant system - Head Gaskets?

For whatever reasons, it sounds like a classic low-water boil-over. When running, the water temp got up pretty high, but not boiling. when shut off, all cooling stops other than radiation from the block. So what water was there started to boil, with the trapped and growing steam helping do a "big vomit". I could hazard a guess that your temp gauge may not have read trouble, if it was out of the solid water area. Or broke/marginal sensor/gauge. But I would lean more towards the water level was WAY down (not good for tranny either, if the only cooler you have is the one in the radiator tank!).

Now, if that is really what happened, why? Is it possible that when replacing A/F you left it air-bound, without a full-fill of A/F, even though it "appeared" full? That could trap a slug of air in the upper hoses/block. All my 302's I had a Prestone Flush'N''Fill tee in the return heater hose, and I could get real close to a fill that way (by burping air out the tee with the tee cap off). Even then, I would still have to add later after some run/cooloff cycles. I always looked in the radiator for a while, then felt I could trust the coolant recovery tank level. A leak in/at ends of recovery hose, or vacuum leak on radiator cap can fool you into thinking everything is OK 'cuz the recovery tank is OK (but radiator could be down, and can't suck A/F back into radiator when cooling down due to a leak under radiator vacuum!).

I Have seen brown in radiators as a sealant, came in new cars for years, would build up crud on sides of recovery tank. Was a favorite in garages after major engine work. But the brown was a build-up, the overall A/F color was stil green. Not saying what you see can't be oil, will be interesting what the crankcase shows... low on oil, loaded with oil and water mix, or OK! (I'm pullin' for the big OK for ya).

Let us know what you find out, and anybody else feel free to jump in...

UncleDon

post #3 of (permalink) Old 10-12-1999, 12:32 PM
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Re: Problem w/Coolant system - Head Gaskets?

My thoughts shadow Uncel Dons. I think that you had an air lock in the block (low water). This has happened many a time to me. Temp gauge says 'normal' but the block is overheated.Took quite awhile for me to fiqure out, just burp it, and be sure your recovery tank is working well.
Good Luck,
Rick-

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