Mystery coolant leak..........95' cruiser

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Mar 17, 2012
Bakersfield CA
Yes, another coolant leak thread. leaks from the rear of the engine off and on. I cant make it leak when its not, and when it is leaking I can't make it stop when at idle. But something happens when it sits or after driving it a few miles.

Fact: It was'nt leaking when taken to the shop. It was at the shop for two weeks for observation---nothing. I get it back and after a week it started again.

While at the shop the coolant system was pressure tested to 20psi---nothing. No oil in the water. No water in the oil. Chemical test shows negative for combustion gasses in radiator. Nothing unusual coming out the tail pipe. The engine runs smooth with no loss in power. I was told it was'nt the head gasket
So here it is....all was good when I got to work. I turned it off and came back an hour later and it had leaked from behind the engine, dripping down off the transmission. I started it up an hour before I got off work to double check and it started to leak (drip drip drip-big drops) again coming off the transmission. After work I got in it and started it up leaking, and by the time I drove home it was NOT noticable loss in coolant level in the coolant recovery tank. Its not a heater hose. The source cannot be seen-its somewhere between the firewall and engine. Thoughts anyone??
Sounds like external HG leak. Just a thought, but probably not leaking while the engine is hot due to metal expanding and sealing the leak. Try searching a bit, there was another member on the forum with a similar leak.
Rear heater pipes?? What side of the transmission are the drips coming from?
+1 on the heater control valve. Looks like its coming From back of the engine. Imperceptible when looking at it from the bay and from underneath.
Sorry I can't read all replies due to pop-ups that don't go away......

I was hoping that there was some way for maybe a leaking heater core to leak on top of the tranny...hmmmm.

It hasn't leaked since last post.

Any thoughts on stop-leak type stuff next time it does leak? It runs great right now.
I'm gonna look at the heater control valve again, but I'm not sure how to go about checking different than watching it as I have when it leaked.
Failing that it might just be a dodgy welch plug on the back of the block - but if it is, the coolant will be dripping out from within the bellhousing. Nowhere else.
Have you checked The (PHH) its a small 3-4” hose located In The back Of The block driver side . Do a search on (PHH) tons Of info on this forum
I believe I have an external HG leak. Still not leaking-it sat for 4 days.......... drove it today and bought HG/block sealer. I am not %100 sure, but I've looked at the PHH and other hoses and that ain't it:bang:

The motor has 241xxx miles on it. I don't want to just do HG with all the miles on everything else. The motor runs really smooth. I would like to see 100K more out of it and then I'll look to do a full tear down. We will see.
Try to avoid the stop leak chemical ... it will eventually stop coolant from flowing in the rad.

Here is another check... look up!! I mean look up at the under-hood insulation and see if it appears wet/dark. If the rad is leaking between the plastic rad top housing and the gasket that seals it to the body (eg rad tubes) it can spray up/be blown up and "could" find its way to the back of the block and leak onto the bell housing/transmission assy. - this did happen to me fwiw.

Also as others have said - For sure check the heater control valve and rear heater hoses
So someone said look up............

Not saying the issue is fixed but I looked up at the hood insulation. I thought no way. Then I noticed coolant on the top of the radiator. I wasnt sure if it was from me or.........

So I drove a few miles home reving the engine high to build as much pressure as I could in the cooling system. I popped the hood to see a stream of high pressure coolant coming from the top of the radiator between the plastic top tank and the aluminium.............

I ordered a radiator from orileys. It needed a few adjustments to fit but its in. I replaced the drive belts while i was at it and cleaned up the engine bay too.

No coolant leaks so far-knock on wood. :beer:
Good find, interesting how that worked out.
Glad it worked out for you so far.
For peace of mind I would replace the heater control valve and associated hoses, if they have not been done.
It's cheap and easy!
I hope this note is not premature (or jinxes the fix) but I am really pleased that my experience has helped someone else. I have certainly got a lot of great tips and help on this site. And I have found some weird things can happen that point you in the wrong direction (see my note on my faulty Crankshaft Positioning Sensor - CPS)

Take care ... BTW - although the new rad has fixed my leak seen at the bell housing ... I still peak under the truck every few days ... "just in case"

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