Question About GM 4.3 Vortech V6 Cooling.

Looking for info to diagnose an overheating problem on a '96 GMC 4.3 V6 Vortech.

Earlier this week we had some abnormally high temps and noticed my truck starting to overheat. I pulled out of traffic to let it cool down and opened the hood finding a (not so nice) spewing of coolant from the water outlet. OK, it's obviously needs replacing and the thermostat will be done at the same time. More interesting is that I've not been able to replicate the problem with truck running at idle since then, but I'm not crazy about taking it out in traffic either. Running it at idle only produced a very small leak in the outlet where the pipe meets the flange on top of the t-stat.

What I'm most curious about, aside from what caused the problem in the first place, is the direction of water flow in the system. Does the coolant flow from the t-stat to the heads or from the heads towards the t-stat?

I'm kinda thinking it flow towards the t-stat, it failed in a closed position and forced the coolant through a weak point in the outlet. Am I wrong in this thinking?

Anyone else with experience and insight gets a hearty "thanks in advance".

TIA.

Does that thing have Dexcool? If it does, that's your problem

most likely an intake gasket has been weeping, and when the level got low enough, it overheated when they overheat the steam does some nasty things to hoses and gaskets. oh and the coolant flows from the heats to the t stat

In reply to tuna55:

None; that crap was thoroughly flushed and replaced with the good ole stuff.

In reply to warpedredneck:

Thanks for the heads-up.

Any idea on the potential for bigger damage and where to expect it?

AFAIK the 4.3 never got the reverse-flow cooling system like the LT1, so the path is radiator lower hose -> water pump inlet -> block -> heads -> intake -> thermostat -> radiator upper hose -> radiator -> lather, rinse, repeat.

First, don't mess around trying to get it to overheat at idle to see where it leaks, get a pressure tester so you can pump up the pressure till it leaks to see where it comes from and what pressure it leaks at ( I would expect to see it leak before you get to rad cap pressure) then you don't have boiling coolant and a hot motor to deal with when you're digging around.

In reply to Strizzo:

That's good advice and with three older vehicles it seems like a darn good idea.

A quick look at the NAPA and AutoZone websites show Balkamp and Mityvac test kits for $50-$60. Are either of these worth considering?

in extreme cases the head gaskets will have turned to mush, 8 out of 10 times for me, i change the intake gaskets, all the hoses, new t stat, reassemble the engine run it for 20 minutes to half an hour with fresh oil, filter & gm cleens. flush the oil, (just in case there was any coolant in the oil) and good to go, this is of course after verfiying the leak/leaks and a pressure tester is a nice way of finding leaks

AngryCorvair wrote: AFAIK the 4.3 never got the reverse-flow cooling system like the LT1, so the path is radiator lower hose -> water pump inlet -> block -> heads -> intake -> thermostat -> radiator upper hose -> radiator -> lather, rinse, repeat.

What is reverse flow about that ? sounds like normal flow to me.

iceracer wrote:

AngryCorvair wrote: AFAIK the 4.3 never got the reverse-flow cooling system like the LT1, so the path is radiator lower hose -> water pump inlet -> block -> heads -> intake -> thermostat -> radiator upper hose -> radiator -> lather, rinse, repeat.

What is reverse flow about that ? sounds like normal flow to me.

That is, I believe, what he's saying.

Guess I should stop and reread before I post.