Help! 250, 6 is consuming anti-freeze!

[Matt_305]

Hey there, I haven't posted on here in forever, first and foremost I will say hello again, trying to become more of a regular visitor again now that I'm older and am doing more work around vehicles as of late (starting my mechanics course at community college in September). Since the last time I posted I bought and sold a 1985 Chevrolet Custom Deluxe, 305 with a 3-speed standard on the tree with 404 000km's on it, it was the rustiest truck I've ever seen, but it still worked fairly well. Bought for $160, took everything of use off of it, sold it still running for $200 haha.

Anyway, the concern is rising with my old faithful and reliable driver 1981 Sierra, which is now flawless except for this recent problem. Checking my coolant lately, the rad is usually empty or very close to it, from several hours of driving, no coolant lights are coming, but I've had problems with that sensor before so that's no surprise and the rad bottle is not filled up at all either so it's not boiling over into there. All the hoses, heater core and rad are excellent and not leaking, what's left of the anti-freeze is very clean not sludgy and the oil also looks excellent. The exhaust is not white at all, as it's always been a little blue on start-up but other than that fine. It has to be being consumed in the engine though so my best guess is that the intake manifold might be leaking? There's a hole in it already affecting how I have have the carburator running, if you put a torch by the hole and cut off the leak you can make it run like new. Am I probably guessing right that one of the passages carrying coolant into the engine is probably coroded like the outside airway of it and is now allowing antifreeze into the engine? I have a manifold priced at over $200 if one is still available, the exhaust manifold could definately use replacing (unavailable) and the chokes riostat needs replacing as well (quoted at $180 for that)? I'm thinking I will drive it till it seizes, and put a 305 or 350 in it? Would you guys agree with this at all, or am I expecting the worst from a common problem with these engines? Would it be smart just to put a new engine in now? I guess I'm just looking for opinions haha thanks in advance! -Matt

P.S. I always wanted to change the engine but thanks to recent gas prices I was finally liking the straight 6! haha

[andresco50]

If the anti freeze is in good condition maybe your radiator have a hole, check your radiator hoses and the clamps in the water oulet, the water pump and the seals too...

[ca180]

also check your cap.

[TeamRinaldi]

Check the heater core too. It may be leaking down the firewall instead of in the cab.

[D13]

I'm assuming it's an integral head (intake manifold is part of the head, not just bolted on). Once these get hot once the warp and crack, leading to the vacuum leak you describe.

If it's not integral, the manifolds run $50 or less on E-bay, or a board member may have one.

For the coolant, best bet is to get it pressure checked when warm. Failing availability of a tester (Mityvac and radiator adaptor) check the spark plugs. If a particular one is clean, suspect warped head and blown head gasket.

My L6 went 300K kilometers with no internal work. If the motor still runs good then it's definitely worth putting a few bucks into.

[old Rusty C10]

i agree with d13 and also teamrinaldi.. you could fill up the antifreeze and use a pressure tester to see if you could discover where the leak is..