Intake Gasket or Head Gasket ? Losing Coolant

[98cowlinduct]

OK....A quick summary.

1999 Chevy Suburban 5.7L Vortec 167k Miles but very very
well maintained...very clean engine bay as well.


- Been using coolant for 6 months now, getting a bit worse
- Runs rough at start up, blows white smoke until you drive off and burn it off.
- NO coolant in my oil
- NO hydrocarbons in the antifreeze (tested)
- Had it pressure tested months ago but it didn't show a leak, maybe when the truck warms up it seals? I have not tested it recently.
- NO external leaks

- Cylinder 4 and 6 are the two that are getting wet, i pulled the spark plugs out last night one by one and 4/6 are wet.


Thoughts?

I don't know how the coolant path runs in the motor, so would you say intake gasket or head gasket?
Is there an easy way to tell?

Thank you for your time.

[KJEfting]

Run a compression test on bank #2 to isolate whether or not it's the head gasket. If you get good results, run a coolant pressure test again and you should see it bleed down. It's either a head gasket or a manifold gasket though. Once you get the motor tore down enough to pull the manifold, it only takes an extra fifteen minutes to pull a head anyway.

[98cowlinduct]

I edited my post just before your reply, its cyl 4 and 6 not 2/4

so check those correct?

Thanks

[98cowlinduct]

I was just talking with a mechanic and he was saying it wouldn't be the intake because the coolant runs down the corners.
That the 2 middle cylinders wouldn't be wet.

Probably a head gasket.

Your thoughts on that?

I'm going with both.

[KJEfting]

He's right, the water jackets are near the outside of the manifold, however the pressure from the water pump combined with the vacuum from the intake could very easily drive the coolant up into the chambers for #4 and #6. Do those compression tests and post up the results. You can isolate it from there.

[98cowlinduct]

Thank you for the feedback.

I probably won't get to check it until Saturday but I will report back my findings on the 4 cylinders.

[Dudes99]

Argh!, so here I am searching on a coolant leak on my 99 burb and I run across this. Mine is leaking down the back of the block on the corners, both sides..... probably intake gasket? Any writeups on a tear down and replacement?

[NoEcm]

http://www.market-place.com/intake/intake.htm

http://www.automotiveforums.com/vbul...t=338753&pp=15

http://www.fullsizechevy.com/forums/...-99-tahoe.html

[98cowlinduct]

Mine ended up being head gaskets

The passenger side head was cracked on the exhaust seats, cylinder 4 & 6 was wet from that, 7 was getting wet from the headgasket leaking.

All better!!!

[throttleunkie1]

Originally Posted by KJEfting

It's either a head gasket or a manifold gasket though. Once you get the motor tore down enough to pull the manifold, it only takes an extra fifteen minutes to pull a head anyway.

LOL! Putting them on is another story though!

[Heavytruck]

Here's what I have on this subject. My 02 van, 5.7 l31. Leaking down back of block. Intake gasket. The factory gasket is plastic with silicone rings around the ports. I spoke with a tech at fel- who also had been an engineer at GM. He told me that in a truck application the block flexes too much and the gasket leaks possibly even cracking, the dexcool gets by even pitting the aluminum. The engine vibrations even will wear ring grooves around each port. If excesive, the heads need removed and machined. Felpro makes an improved truck gasket, steel sealed in a silicone rubber, and anti-crush spacers at the bolt holes.....My 99 grand prix, no external leaks, just lots of smoking. It seems as though the antifreeze had pitted an area where coolant flows through the plenum via near the throttle body.I replaced the prenum to intake gasket and plenum to throttle body gasket, as well as oil and coolant system flush. All better now. i hope this helps.

[KJEfting]

LOL! Putting them on is another story though!

True, true. Yeah, Murphy's law comes into play too. "Whatever can go wrong, will." ie. head bolts breaking off...

[caselesss]

alright i changed my intake gasket this weekend and that was the problem like i expected. put it all back together and let in sit 24 hours before starting it. went out and turn the key and nothing. did i miss something? we hooked everything back up right or so i thought. is the ignition on these things all computerized and now the computer needs reset? it doesnt even start to turn over it just clicks when i turn the key and we even put he charger on it and set it to crank and still got nothing. i know its a vague question but any ideas?

[Heavytruck]

If you suspected coolant was leaking into a cylinder(as opposed to an external leak), you may still have a cylinder with some in it. Unlike a wisp of gasoline, water doesn't compress. If the valves are closed(compression stroke), the engine won't crank, if it does there is risk of engine damage. Before I took my grand prix to my bros house to work on it, I pulled the plugs and cranked it over, then reinstalled them and fired it up.

[BarnDustR10]

Although every single person on here will tell you it's intake leaking, it could be the head gaskets. I know I went and looked directly at mine pissing out the back of the heads , but nope apparantely i have double vision because it can't be leaking there. I did intake and head gaskets, problem solved.

[throttleunkie1]

How many volts is your guage reading in the dash reading? That little light bulb under the hood that turns on when the hood is up will drain a battery over a good long day of working on it (if you happened to leave the battery hooked up during the whole process).

[caselesss]

thanks guys it ended up being a ground wire on the underneath the alternator had broke off. that is the lead that goes to the starter thats why the battery was fine and it still wouldnt start.