TahoeMatt

I've been adding antifreeze over the last week ( when I was driving it / 99 Tahoe 5.7L Automatic ) over and over and it keeps disappearing.... It's not leaking on the ground. There's no major coolant/seal/water pump leak that would dump that much out....nor is there a constant leak while sitting or when driving that I've noticed..

This combined with the fact that it is sputtering/missing when I drive it...

There are no codes coming up.

Checked the fuel pressure and it's fine. Replaced the injector spider, fuel pump and filter are fresh.... basic tune up not to long ago.....

Anyone have any ideas on what this could possibly be ?

I'm going to check the compression tomorrow.



Thanks !!!

shamrock246

What color is your oil?The lower intake gaskets are known to leak and coolant can travel along the the failing gasket and be sucked in the intake port or it goes into your oil

If the compression is good i would replace the intake gaskets with these
Felpro/Intake Manifold Gasket (MS98000T) | 1997 Chevrolet K1500 1/2ton Sub 4WD 8 Cylinders R 5.7L SFI | AutoZone.com_

TahoeMatt

Thanx for the input.

Oil was still dark but runny like there is antifreeze in it....

Yeah checked the compression and it was good. The drivers side was a lil lower around 90 and the guage wouldn't hold pressure after I turned it off.... so I assume a def. leak in the gasket...

Any additive to put in there to seal the break for mean time until I can rip that sucker apart ? Does anyone have a good DIY for the lower intake gasket ?

Thanx !!!!!!!

shamrock246

Stop leak probably woun't do anything if you google the procedure there is lots of info out there about changing them,make sure you mark that distributor rotor while the engine it set with #1 cyl at tdc on the compression stroke the timing is set with a scanner and inspect the distributor gear for wear while you have it out they tend knife edge


OBS Intake Gasket Replacement (many pics) - Chevy Truck Forum | GMC Truck Forum - GmFullsize.com

UNDERSCORE

Lost the motor to my 96 Sub that way. Sucks.

TahoeMatt

Thanx for the info. Yeah I'm a little nervous about having f'ing antifreeze in my oil. wtf.
How do you tell if it's the compression stroke or the opposite on #1 ?
I'm gonna do some hunting around and see what I can come up with.

Earth Rider

If you're experiencing antifreeze in crankcase I would recommend not running the engine at all. I don't believe "additives" will help at all. Main bearings may become damaged resulting in more expense to repair. If running and coolant is expelled or low it will overheat quickly and could result in lower intake manifold warping.

At and after 80,000 miles it appears 5.7 li VIN R v-8's are prone to lower intake manifold gasket failures. Usually any or all three types of leaks may occur: into crankcase, into combustion chamber and external.

FelPro MS98000T intake gasket sets are metal/rubber vs factory plastic like material and appear ideal to seal especially if minor surface irregularities on lower manifold to cylinder head surfaces exist (possibly from corrosion).

As mentioned, it is critical to index and mark distributor so when putting it back in it is "exactly" in same position as before removed. It will throw error codes if not exact. (Something like 2 degrees leeway)

Might consider taking lots of photos before and during tearing into it. It definately helps on reassembly.