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I have a 98 GMC K-2500, 5.7 350 with 104,000 miles. It has been losing coolant for a little while now. I get white smoke out of the tailpipe and drips of water at an idle. Just changed the oil this morning and no water or coolant in the pan. Is there an easy way to tell which gasket is leaking?

ps- Chris thanks.
 

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I'd pull the intake and see what you find.If you see evidence of it leaking,then I'd button it back up with a new gasket.If not,then you'll have to pull the heads and take a look.

Normally the intakes leak externally,or into the lifter valley,where you would see coolant in the oil.You still have nothing to lose by pulling the intake,as it has to come off to do the heads.
 

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In addition to what Chris said, on the Vortec engines (96+) this is a very common problem. I have seen several of them begin to leak around the intake manifold. I think its usually leaking externally out the rear. If there is white smoke in the exhaust, when its above 50°F, then you probably have a problem. It there is a little white 'smoke' when its cold outside, then it doesn't nessecarily mean that you have coolant leakin in the engine, it could just be excessive moisture due to atmospheric conditions.
 

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I have had the same problem with my 98 Sierra. I just pulled the manifold off. What are some of the signs for manifold gasket leaks?

Its been a long time since I have taken a manifold off anything! Were do I put the RTV silicone? I think I am supposed to put RTV on the front and rear rubber manifold gaskets, but do I put RTV on the manifold gaskets themselves. From memory, I thought you just put dabbs of RTV on the gaskets, to hold them in place, while installing the manifold. Also, does anyone know what the torq. specs. are for the manifold bolts - and the manifold intake bolts?

Lastly, does this vehical need to have the timing checked after I put everything back together.

Thanks Chuck B.
 

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word of advice, after you do the intake, flush the cooling system really good then refill it with the green anti-freeze!!! save your water pump, radiator, and the entire engine!! get that dex-cool out!! i see it destroy engine's everyday!!
 

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check your radiator, if it has brown krusty stuff in it, it maybe to late! dex-cool has taken it's toll on the engine. GM says it's a extended life coolant good for 150K miles, have yet to see it last longer then 75K miles!! the best thing about dex-cool is it makes our shop alot of $$$$$ best thing since sugar in the gas tank.
 

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I will agree on the Dexcool,it just doesn't work in some engines.The 4.3L were the worst.

Use the RTV in place of the end seals,no rubber at all.Just a nice 1/4 bead will seal both ends.Iwouldn't recommend using it on the intake gaskets,unless the gasket surfaces are really pitted around the coolant passages.Adding RTV to gaskets may cause early failure.

If you marked the dist dead on,you shouldn't have to check timing.If your a degree or two off,it won't hurt.
 

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Definitely the intake gasket, IMO.Every one of the Vortecs do that.I'd flush the dexcool out of it as soon as the engine goes out of warranty at 36000 miles. Chris,funny you mentioned how its worse in the 4.3s.I seem to nitice the same thing.I thought it was just coincidence.
 

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GM had a bulletin on the 4.3's it was so bad.Guess it has to do with the metal composition of the block or something.

I have had a few,that we flushed,and flushed,and flushed,and even the green stuff turns to rusty mud in a few weeks.Can't seem to get rid of it.
 

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the 4.3 had so many problems with blockage
that the dealer has been replacing engines
we never refill with dex-cool after flushing the
cooling system
john
 

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I have a 96 5.7 GM and it has in the past looked like someone with a bad case of the runs sat ontop of my coolant overflow tank and couldnt hold it in anymore.


Now i know what it really is.. Not that this news is any better to me i would propably be better off with what i thought it was in the 1st place.

Tighten the hose clamps on the air intake hose going to the intake manifold. The shop that fixed my truck didnt do that when the fixed the gasket and it caused me truck to act like i was beeing hit from the rear as soon as i went over 60Km it would start. I had a friend look over the truck after the work was done, he tightned the hose clamp and no problem anymore.
 
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