Are there any mechanics on this forum?

powermad · Dec 3, 2012

Unless SBC's have changed drastically in the last 20 years..
The waterpump and all the brackets are already out of the way to remove the head.
Remove the balancer and timing cover is all that is left.
I've seen way to many timing set failures to not do this on higher mileage engines.
The nylon sprocket is junk and wears out very fast.
You are looking at maybe another 30 minutes to replace it and maybe another $35 in parts.

If you are going to just piece it together to sell it is one thing. If you are looking to keep it around it is a good idea to do it while you are in there.

powermad · Dec 3, 2012

The intake manifold gaskets do leak, but generally you see them leaking on the outside and the coolant runs down the intake and runs down the back of the block due that whole gravity thing.
If left leaking long enough it will start to go into the pan as well and mix with the oil.
If coolant is coming out the exhaust then most likely it is a blown gasket or a cracked head.

Proper diagnosis would be best.
A cracked head or blown gasket is pretty easy to diagnose.
I would first start with making sure the coolant is full, remove the cap and start the engine.
If coolant starts to do the ol faithful routine or there are air bubbles coming up as the engine comes up to temp then you have a gasket/head issue.

Pull all the plugs on the bank that is leaking and do a compression test. The coolant fouled plug is a dead give away on the problem cylinder.
If you don't have a compression tester just hold your finger over the spark plug hole while the engine is being cranked over. It will either have compression or it won't.
Most likely the head cracked by a water jacket and went to the combustion chamber.
Pretty common on those heads.
Been working on Chevy's for 30 years. Not much mystery to them anymore.

powermad · Dec 3, 2012

Now here's a jigsaw puzzle.
1973 Kenworth with a 1989 Bigcam IV Cummins.

Redcap · Dec 3, 2012

powermad said:
Now here's a jigsaw puzzle.
1973 Kenworth with a 1989 Bigcam IV Cummins.

I'll see your Big Cam IV and raise you a Mack E9.

powermad · Dec 3, 2012

Ah, V8 Mack engines. I work For Mack and Volvo.
Used to work on them all the time, not so much anymore. Or any of the older stuff for that matter.

Ironbar · Dec 3, 2012

For the record, what was happening prior to this past Sunday was that coolant was definitely leaking into the exhaust. There were NO external leaks whatsoever. No indication on the engine, and no puddles on the ground. There was no leak into the engine oil. I watched it very carefully for signs of leaking in to the engine itself. Nothing there. I kept having to add coolant to the radiator every time I drove it. Had to add more and more as time went by until Sunday when coolant filled white smoke came pouring out of the exhaust, and I started overheating.

So from all the replies on this thread, I'm gathering that it could be a blown head gasket, a blown intake manifold gasket, a cracked head, or any combination of the three- correct?

powermad · Dec 3, 2012

From your description I would bet on a cracked head.
There is no way a leaking intake manifold gasket will allow coolant into a cylinder.
The coolant ports are at the front and rear of the head. The intake ports are towards the middle.
Used heads are cheap if it is cracked.

sheepdip · Dec 3, 2012

yup, thats pretty much it. pull the spark plugs and put some water in it, pressurize the system if it will hold pressure and see where the water comes out.

Redcap · Dec 3, 2012

powermad said:
From your description I would bet on a cracked head.
There is no way a leaking intake manifold gasket will allow coolant into a cylinder.
The coolant ports are at the front and rear of the head. The intake ports are towards the middle.
Used heads are cheap if it is cracked.

And smallblock chevy heads are plentiful.

bobu · Dec 4, 2012

The key here is to be sure that you identify the problem when you do the repair, and complete the repair in a way that you know that you have fixed the problem and not created new problems. My son had a toyota tacoma with a 3.4L v6 which had a slow coolant loss that we chased for some time involving replacing the radiator when we found signs of a slow leak, then the cap as it pressure checked low. There was a slight antifreeze smell but never any signs of antifreeze on the garage floor, we finally concluded that it had to be head gasket leak. As we were tearing it down we found a steel by-pass tube between the block and the intake manifold that had been obviously leaking (no open valley like a SBC) so the antifreeze would basicly evaporate as it leaked. We were far enough into it that we went ahead and pulled the heads to be sure that we would have the problem 100% corrected and found all to be well. Put it all back togeter and no more antifreeze loss. I have had several 3.4's apart and never thoght about that heater bypass tube or any aspect of the intake until we were into this particular job.
OK, so that being said. Intake and heads will need to come off, inspect all gaskets and surfaces for signs of leakage, if a leakage is identified clean all surfaces and check with a straight edge, inspect heads thoroghly and re-assemble. If no gasket leakage is detected ,and you can not see the problem with a head, take them to a reputable machine shop. I have used a company in Portland called "Cylinder head service" if I remembered the name correctly, the are on MLK. I have bought over a dozen long blocks from them over the years (last one was 6 years ago) and they do a great job and are very reasonable. Buy a set of rebuilt heads and put it back together. Now drive it without worries of revisiting this problem.
You need to realize that any used parts that you install are likely only as good as the ones you had the day before it failed. Chevy changed to the Vortec design in 96 and the heads will not interchange without other changes, so you are looking at buying used parts that are at least 16 years old.

NOTE: Make sure that you take a look at cylinder bores etc while it is apart just to be sure you know where you are at on overall engine condition.