I'm at wits-end with my 97 z28. Cold I can top off and bleed the cooling system and the car runs fine...it does blow some white smoke at startup...but never runs past 190. I have a new water pump, 160 thermostat and madz28 tune, checked the radiator flow and leakdown test...all ok.

When you let the car sit after running fine, even for only an hour or 2, the temp guage shoots up to 245 right away, and is low on antifreeze in the radiator. It doesn't seem to draw out of the overflow, and if I open the bleeder valves it just steams out and doesn't bleed, and the heat blows cold.

I have a manifold oil leak, and was wondering (hoping?) if that could be causing the loss of my antifreeze when the car warms up, or if I blew a head gasket. Would anyone recommend just resealing the manifold or should I pull the heads to be sure when I tear it down?

Any help would be great.
Thanks

 

any oil in water or water in oil?

Given the amout of anitfreeze your loosing it should be smoking quite badly - perhaps ther is a rad or hose leak that is only apparent when the system is under pressure.

the intake oil leak should have no impact on the cooling system - but if you can not find the issue before you tear into it - you may want to replace the head gaskets just to be sure.
It will run you a hundred or so on gaskets and new bolts

 

I'm not sure of your comment in your last paragraph. Sounds like you were referring to an 'internal' intake manifold leak, where oil leaks into the intake runners, or coolant into the lifter valley. Those problems are pretty much limited to older gen I small blocks since LT1's dont have coolant passages in the intake and the gaskets have rubber seals around the intake runners. Haven't seen one leak yet.

First things first, where's the coolant going? One of three places...it's evaporating, which could be picked up by the 02 sensor and misinterpreted as condensation in the exhaust; it's internal, which would be very bad if it was run with oil for a long time. Check for frothy or milky brown oil...(coolant kills engine bearings); it's external, and it's leaking out as the engine is revved (pressure), or as it heats up (expansion). Coolant can be leaking out onto the ground or into the passenger compartment through the heater core under or over the carpet(interior muggy, hear water moving around, smells sweet inside)

Sounds like you have accelerated seepage past your head gasket. You could try some of that sealer to slow it down if it's still at a manageable level. Dont use more than one. It could be leaking past the gasket into the crankcase, or into a cylinder a burning. Most older small blocks had a problem with valveguide wear and they'd give an oily puff at startup, but the newer Vortec's and LT1's dont seem to have this problem. Condensation in the exhaust pipes or muffler is common when you start a cold car up in the morning, but does it do it during a mid-day hot start?

white smoke is usually coolant, BTW. Maybe you can top the car of and let it idle for an hour? I would say have it pressure tested as there are tools for that, but at an hour's worth of labor, there are other ways to do it...

dont run it too long at 245 or higher or you might warp the head surface...hopefully this gives you some idea where to look. I you do the head gaskets make sure you surface the heads. This is a good chance to go to a thinner gasket for a tighter quench, like a MRG-5716 or impala SS head gasket. The 5716 with surfaced heads gives you like 11.2:1 (I think)...

 

Thanks for the responses all. Aye I'm getting the dreaded white smoke at startup, but doesn't smoke excessively when the car is cold but will when it's hot. I was hoping, since the dealer said the intake leak could be a problem, that maybe the issue was a big air pocket or 2 in the cooling system due to air entering via the manifold leak, but it's wishfull thinking on my part since I couldn't seem to work out all the air without it overheating.

The motor has 54K on it, is it worth pulling the whole motor for a fresh set of rings and bearings, as well as a new clutch? I figure this would be a great time for a cam and header install lol, and plan on doing that at least.

Finally, if I do pull the entire motor, is it possible to not disrupt the AC, i.e. bleed the system? I would pull the motor only...

Thanks again.

 

my brother just blew a head gasket and we replaced it. I never thought it would take that long to get the heads off. We had to take almost everything off of the engine. It was a ford enough said. and he was shooting water out the exhaust. let it sit for a while and start it up see if it shoots water out. Good luck

 

New developments here...The last few times I started the car cold there was no white smoke...and I talked to my machinist, who had said my intake leak could be the cause of my problem...It only acts up and overheats when the car is hot for some time. I'm going to use a CO2 coolant tester, and then pull the intake and plugs. Keeping myfingers crossed the head gasket is still good. Has anyone heard of the intake causing my problem, w/ one of the runners close to a manifold water jacket, which when heated lets air into the cooling system and some fluid into one of the cylinders?

 

In my book that would occur if you had a blown head gasket.
Coolant is either going directly into the cyl - giving white smoke or leaking into the intake and down to the lifter valley and to the oil pan.

how does the oil look?

the intake is independent of the cooling system - water flows through the heads but not through the intake

 

The guy you are talking to apparently knows nothing about LT1s. Listen to what everyone is trying to tell you-that there is no water in the intake!

If you have air getting in the system, loss of coolant and it is not dripping out by an external leak, that leaves only the head gaskets as suspect, IMO. Where else could it be going, but being burned during combustion?

 

I agree. I think that you need to find new people to deal with. There is no coolant crossover in the intake. You have one that runs in the back of the heads connected by a tube, and you have the passages in the water pump for the thermostat. None in the intake at all.

If it's leaking to the extent you're running hot and there's no water on the ground, either it's building up on your passenger floor (you'd notice), or it's being burned in the chambers. I bet if you pull the head you'd see clean spots in one or two chambers...which happens when you get a coolant leak into a cylinder...