4.3L General Oil Useage Question

[98 Formula FB]

This isn't an LS motor question obviously, but I'm not an active member of any other land vehicle forums, and I'm sure there are people on here who know...

I've got an '89 GMC C1500 that I've had since '02. It had 166k on it when I got it, and has 225k now. Early on, there was a problem with moisture on the oil dipstick, the rpms being too slow to come down between shifts (5-speed), and occasional rough running.

I checked compression (good) and changed the intake manifold gaskets. Also had it to a shop where it got a new ECM (not sure which happened first).

I think the engine has been worn out for a while now - it uses oil very quickly (like a quart every few hundred miles) and turns it black fast too. But it's a little odd to me that it fires right up even after sitting for weeks, runs pretty well, and has as much power as it ever had since I've owned it (far from enough, lol).

My question is really this - is there another route the oil could be escaping by besides past the rings? I've probably changed the PCV valve, maybe more than once. Another compression check may tell me a lot of things, when/if I ever get around to that.

I tried running 20W-50 oil in it once (which is approved in the manual I believe) to see if it'd slow the oil use, but the engine got hot, to the point of boiling the coolant in the overflow tank.

A weird behavior this truck has done relates to the moisture on the dipstick - it's present sometimes, sometimes not; and believe it or not, in the last several years, there seems to be an engine roughness (and less oil useage) that goes with it being present, and engine smoothness (and drinking oil like a fish through water) when it's not there.

I've never heard of such a thing, but I wonder if that is emissions controls related somehow.

I know an old TBI motor is out of the purview of guys on an LS forum, but maybe someone here would have an idea that would explain the above. We had an '88 Astro with the 4.3L for years too that never acted like this - always ran well and never had any moisture on the dipstick; just began to use oil when mileage was in the 170k's if I remember right.

Thanks...

[SMWS6TA]

Your 4.3 falls in the time frame that those engines had a valve stem issue with high mileage. Might be time to freshen up the heads is they've never been off.

[98 Formula FB]

So like just valve stem seals and O-rings, or more extensive work than that?

I've never done that but I've got another engine that needs it done too ('75 400sbc with about 200k, in a '74 GMC C10). That one acts a little different, fouls the plugs and uses some oil, but doesn't turn it black as quickly as the 4.3.

That would probably explain where the oil was going in the '88 Astro I mentioned too.

[SMWS6TA]

pull the heads and have a good engine shop freshen them up. I paid about $80 for my 243 heads when I did my build.

If you do so, look at the cyl wall cross hatch. It will give you an idea if the rings are worn out too.

[98 Formula FB]

Ok, thanks.

[SMWS6TA]

4.3's are a solid little motor, just needs a little love with that much miles is all.


I had an 02 Blazer that blew a hose and drained all the coolant out on the side of the interstate. I swapped the hose, refilled it with coolant and limped it home. I had just done a complete head gasket and upper manifold rebuild as well as refreshing the heads and removing the peanut butter consistency of oil and coolant mixture from a blown head gasket that had sat for a yr till I got it. I thought that as bad as the coolant blew out, it might have warped the head or cook the engine. Nothing. After new hoses and coolant it ran like a champ till it got killed by another van hitting me.

[98 Formula FB]

Yeah, I've never been happy with the power, but I'd like to keep it going. I actually picked up a cheap 5.0L Caprice with the idea of swapping the motor into my truck, but it turned out to be too good of a car to scrap, which left me back where I was - just driving it once in a while to keep the rest of it operating, and feeding it oil.

[SMWS6TA]

whispering.......LS swap......

[98 Formula FB]

Lol. Yeah, if my son messes around too long, I'll have to make him an offer he can't refuse on his Firebird. He needs to clean the leaves out of it and at least start it and move it around once in a while, but it's just sitting.