1998 V6 4.3 Vortec just hit 80k mi.

Did an oil change, transmission flush/change and differential oil change.

Over the last 2 years I've noticed that I go through 1-2 gallons of coolant a winter, yet I can't every find any leaks in the hoses, radiator or anything else. Tried replacing the rad cap thinking that was the problem, no improvement.

Changing the oil, it had horrible sludge, and it was only about 2000mi since my last oil change (but it was more than 6 months ago).

Any general ideas on what is causing the sludge? Is it possible my coolant is getting mixed with the oil or is this 2 seperate unrelated problems?

 

My bet is that you have a bad intake manifold gasket and it's leaking coolant. This is a typical failure on the Vortec V6 and I wrote a fixit procedure that's in the DIY section.

If you walk past the front end and smell antifreeze, then it's probably leaking outside the motor. That's good, as you can ignore it for a while.

Pull the dipstick immediately after you've run it and see if your oil looks grey or frothy. If so, it's leaking into the motor and contaminating the oil, that requires an immediate gasket replacement.

I'm not sure about the reason for the sludge, but it makes me suspicious of an internal leak. OTOH, I don't think antifreeze would cause oil sludge. I'd reocmmend using an engine cleaner and changing oil 2-3 times at 500-10000 mile intervals to clean things up.

If you can't find the leak, go to a radiator ship and have them use a pump to pressurize the system - that often forces the leak to appear, or to become audible through bubbling noise.

 

I have had that problem too, but its not just on the V6 that its common. The gasket was made of the same material from 1996 to 2004. Replace the gasket with a cutout gasket, it'll never fail again.

The sludge problem is probably from the coolant mixing with the oil. That's from the rule of not mixing orange coolant with green coolant, green coolant has petroleum oil and orange has mineral oil and when they come in contact with each other theymake a very acidic jelly that will cause interior of radiator to rust.

As for the sludge, Isuggestadding ZMax or Marvel Mystery oil.

If your problem isn't the gasket, drain the system, get a smoke machine and seal the tip of the hose inside the reservoir in a few minutes youll see if there is a leak. Doing it yourself always saves money.

 

Not true on the coolant. But the rest is good.

 

Hi Im new on the forum. I found this thread via Google.
I own a 1991 Silverado with a 4.3l Vortec. Not exactly a Blazer but basicly same engine.
The thing is that the problem I have with my engine is allmost the same as "PawNtheSandman".
Does the 1991 Vortec has the same typical problems with intake gasket as the newer ones?

Description of my problem.
When pulling the dipstick it has some sludge on it and even a few water drops. The end of the dipstick (under the handle) is severly corroded by rust.
When I did my last oilchange the oil seamed fine when I emptied the pan until the last of itthat came out. It was clearly mixed with water. Whitebrownish to its color
At the front of the intake it looks like an old leak of some kind. Doesnt leak now but must have leaked at some point.
When inspecting the valvecovers it has no sludge on the inside,but a black almost sandy oilresidue.
My oilpreasure is fine but the gauge is sometimes sticking to the max or behaves irratic.
No sounds from engine and itruns good. Just has a ticking noise from the distributor area.
No white smoke from exhaust
Havent noticed any missing coolant, at leastuntil today.The coolant however has a few oildrops in it, mainly in the coolant recovery bottle

Daniel from Sweden

 

Definitely sounds like an intake manifold leak to me. If head gaskets are suspected, then a quick compression check would confirm it. If one or more cylinders are abnormally lower than the rest, then you have a head gasket failure.

 

Thanks. What I suspected then. Is a little bit worried though now since the car has been running with this for atleast six months or more.

Is there necessary to do any thinkering with the computer after removing the intakemainfold? I mainly works on vintage american cars and dont have any experince of newer electronics.

 

Nope, just disassemble, clean, reassemble and refill, making sure to get all of the air out of the system. I'd recommend installing a new thermostat and a new radiator cap as well. You'll probably want to run an engine flush through the oil to make sure that you get all of the contamination out. I wouldn't be surprised if the bearings are hurting after running with that much water in the oil for that length of time...