I'm going to look at a '99 chevy truck, 5.7 sbc, 175k miles, Wednesday afternoon. I was told that the only problem with it is that it overheats. The owner is old and sickly and doesn't want to mess with it any more, and this is all the information that I have at thius point. It looks good in the pics, but i have no other information at this time. My spider senses are tingling, it could be a steal.
So what are all the likely causes (obvious and not so obvious) of overheating for a 5.7 , as well other things that could be mistaken for overheating?
I'm going to assume for now that no one is lazy enough to give up on a otherwise decent vehicle just because of a stuck T-stat. I know in the real world that is a possibility though.
'99 was in the heart of the dexcool contamination years wasn't it? What would be a worst case scenario with bad dexcool in an SBC? What are the common less than worse case problems specific to the SBCs?
Is there anything outside the cooling system that could cause overheat like symptoms? Like distributor off a tooth, or a fueling problem?
Water pump or fan clutch.
Or someone dumped regular antifreeze on top of Dexcool.
Radiator and/or AC condenser fins full of E36 M3.
When does it overheat? If it only does it when moving, then make sure the airdam under the bumper and skidplate are in place.
Who cares. For what it costs you could put another engine in it for peanuts...
Intake gaskets. My boss has a 98 with 200k on it, seems too need intake gaskets every 75-80k
Cooling system not taking well to being trained to run a gallon low?
This is smack dab in the era of failing intake gaskets. Unlike people with 3100/3400s, truck people tend to be too cheap to fix leaky intake gaskets so they just let it run low. Unfortunately this entrains the coolant with air, and Dexcool can create mud if you do that. I have seen K1500 radiators where the bottom four inches was solid with brown mud. I have also seen head gasket passages plugged solid. (And I pulled apart an LS1 where the head gasket actually blew out its passages in a few places, so coolant was short-circuiting the system and starving the rear cylinders of cooling)
Yes I realize my answer is a real d-bag catchall of an answer, about one shade better than saying "It's overheating because it is too hot". But really, the main reason 5700 Vortecs overheat is a lack of concern for basic maintenance by the owner.
In reply to Knurled:
So suppose it is that bad, would a set of top end gaskets, flushing the crap out and a radiator give me a good chance at a win?
Unrelated to the cooling problem, I just found out that this uses the spider type fuel injection. I thought only the 4.3s had that junk, if I were pulling the top end apart for gaskets, that system needs some maintenance too, right?
Intake gaskets cause overheating because they have a slow steady coolant leak that cause the top half of the cooling system to have more air than coolant all the time correct? Where does the coolant go?
If its cheap and solid, just by it and figure it out later. When later comes, start with the easy stuff t-stat, pressure test and make sure its full of good coolant.
HappyAndy wrote:
In reply to Knurled:
So suppose it is that bad, would a set of top end gaskets, flushing the crap out and a radiator give me a good chance at a win?
If that's the problem, yeah. Oddly enough, if you fix problems as they turn up, cars tend to be pretty reliable 
If/when the intake gaskets leak, get the aluminum backed gaskets which never fail. Do a thorough job of cleaning the holes in the manifold, the threads in the heads, and the threads/underside of the heads of the bolts. Blue Loctite on the threads and follow torque specs and order exactly. You WILL be repairing the car if you do this. The intakes only fail if plastic-backed gaskets are used, never metal-backed, and overtorquing or undertorquing the intake is a guaranteed failure. The torque spec is rather low so screwing it up is easy if you don't have an inch-pounds torque wrench. The manifold is only held down by eight bolts, and it is aluminum vs. the iron heads and block, so it is going to move around a bit with every heat cycle so the gaskets and bolts MUST accomodate this. Undertorque and they leak, overtorque and they destroy the gaskets and leak, use plastic and heat cycles will wreck the gasket anyway and it leaks.
Unrelated to the cooling problem, I just found out that this uses the spider type fuel injection. I thought only the 4.3s had that junk, if I were pulling the top end apart for gaskets, that system needs some maintenance too, right?
Eh. Problems are extremely rare IME. If the regulator diaphragm isn't torn and heaving fuel everywhere (will see a trail of clean underneath it) I would just ignore it.
GM made a bazillion of these things and truck owners tend to whine a lot, err complain about everything, err be very cost-sensitive, so you hear about problems a lot online due to the quantity of vehicles out there. In practice it's pretty robust and works well. The gaskets ARE a constant failure, but people blame it on Dex-Cool because that is an easily visible difference and does cause problems elsewhere, when the real problem is the plastic backing for the gasket O-rings breaking apart, which happens no matter what the coolant is.
Well, it turned out to be a bit of a bust today. It wouldn't start due to a dead battery, and because of the way it was parked, jumper cables to a running engine were not possible. The owner did have head and intake gaskets done in the not to distant past chasing the problem. He thinks it needs an engine. The body and interior were pretty clean. I was a bit off-put by some ghetto-tastic looking repairs under the hood.
The radiator was at least half empty, but didn't have obvious signs of dexcool contamination. I tried to pressure test it, but with the coolant so low, it wasn't a very meaningful test.
Maybe I'll go back next week with a good battery, or maybe I'll just go find something else.
If I had a good 5.7 laying around I'd probably drag it home for a flip project. It looks like it should clean up pretty good
Cracked head, possibly. My 1996 Vortec had one. They typically crack down an exhaust seat and up into the port and water jacket. Fortunately, new assembled heads are something like $300 each.
175,000 miles, 17 years old. Gee, I wonder what the inside of the radiator looks like? Just an automatic replacement as far I'd be concerned.
I'd also pull the thermostat to flush the engine and heater core, probably replace the thermostat while I was at it, and switch it over to conventional glycol coolant.
