5.7 Vortec, oil in antifreeze

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Apr 16, 2007
Cochabamba, Bolivia
I have a '97 K1500 LS Suburban with the 5.7 Vortec with 215K. It burns through about 1 quart/1500 miles. We go from Montana to Seattle quite frequently and it does 80-85 mph fine with all the kids and crap, and gets about 14mpg. It still starts and runs fine with no noticeable problem (no white or blue exhaust, etc). The transmission is still shifting tight or I'd just bag the whole thing. My luck, it'll go soon...

So here's what happened:

I lost a heater hose due to a broken hose clamp at the rear heater and AFAIK, only ever got it up to 210 or so F. It is possible I lost it on the way home from work the night before, but I pay pretty close attention to the gauges. Long story short, I filled up the radiator and there was some oil in the antifreeze. So it has been parked. The engine oil still looks good. I checked the compression and it goes:

8 - 110 7 - 120
6 - 115 5 - 105 (I checked this a couple of times to be sure)
4 - 115 3 - 120
2 - 130 1 - 115

I was thinking of just doing a quick head gasket job. I replaced the garbage intake seal with the Felpro set about 10K ago. There is the slightest possibility that the intake gasket is leaking, but with it being new, and the crappy compression, I'm guessing the #5 is leaking into #3 and #7.

There is also the possibility that the transmission or engine oil cooler is leaking into the radiator. I put air pressure to the engine oil side (because the oil in the radiator appeared to not be ATF) and got no bubbles or any more oil.

Some guys I respect think that it is pretty certain to be the radiator and not the headgasket.

Any ideas?
cracked head - be sure when you go to fix this, that you price a new replacement head rather than machining what you've got (generally, it costs about 1/2 to buy new rather than fix what's there).
With that said, 215k miles is about the natural life of the rings - so you would do well to replace the rings and oil pump. Those motors, with oil coolers, don't have the traditional bore wear that other motors get because they have an oil cooler... which means, rebuilding is cheap and easy (new heads, new rings, new pump, new gaskets) and it's good for another 215k miles.... all for less than $1,000.
Thanks for your reply.

I agree with you that it seems unlikely (given the heater hose) to be the radiator.

Could you explain how you get to cracked head vs. headgasket?
no way of knowing until you pull it apart. With that said, you lost coolant, so it is actually about 50/50 that it's a cracked head - generally head gaskets just go due to manufacturing defect. With that said, I'd also check the oil cooler lines inside the radiator - in any case, it's interesting to me that you don't have the milkshake.

With that said, it's pretty easy to check whether or not it's a head crack/head gasket vs. a cracked radiator... use the test strip, if there's CO in the anti-freeze, it's a head issue... if not, it's a radiator issue.
if you are going to pull the heads..for a perceived head gasket or other issue...for one you have to replace the head gaskets and it just makes sense to have the heads checked for cracks anyway. I certainly would have the heads checked before I spent the time putting them back on the engine..in fact with those miles you should get the heads checked for replaceable parts...new seals etc...potentially springs...
I would never rebuild a pair of Vortec heads, they're an awesome design; because of that design, you can buy brand-new ones for about 1/2 what it would cost for a machine shop to go through them. Getting them checked for cracks is cheap, thus allowing you to bolt them right back on... but if they need any work, again, you can spend $450 for brand new heads delivered to your door or (at least) $750 to rebuild a pair.

Vortec heads are cheap.
I just did this fix on a 4.3 (it's the same issue with the 5.7)

right where the flash is, look at the bottom of where the gasket should be... it's not there, thus it was milkshake oil... it's really a cheap fix ($80 for gaskets) - so it's not a head issue... of course the OP already replaced the intake gaskets (though it could happen twice if he used the cheaper gaskets) - so I'm assuming it's a head issue.

On an unrelated note, this is what Pennzoil motors look like when you open them up.... nice build up, right?

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