cracked block?
 

A couple of months ago I started loosing coolant while the engine was running.
It is up to a gallon every 150 miles. I never found a leak that would make me
loose as much as that. So I kept looking for leaks and trying to fix it with
barrs stop leak. I finally decided it was going out the tail pipes even though
it doesn't smoke. There is pressure building up in the cooling system when
running that will stay over night. This makes me think it isn't from heat
expansion but from cylinder pressures. I've replaced the radiator and the cap,
I've tested the heads for cracks and warpage, I installed new head gaskets and
still have the same problem. The cylinders walls were in very nice condition.
I didn't see any cracks or holes in them when I had the heads off, but I guess
I could have missed something. The spark plugs don't tell me anything. They are
all slightly sooty brown.

I'm not a great mechanic, but what else could it be, other than a cracked
block? There is a miss at idle, but I always thought it was from my defective
distributor.

Anyone have any ideas?

how did you check the heads. you cant see most cracks in a head they have to be magnafluxed just looking isnt good enough

if you were loosing that much thu the cylinders i'd think you'd have a pretty bad running engine with fouled plugs, i'd look at the water pump , heater core ,heater hoses, freeze plugs etc, you can get a type of dye that goes in the coolant to check with a blacklight , i think eastwood sells a kit for it

but if theres pressure building in the cooling system more than usual there isnt an external leak an external leak would stop the pressure from building and losing that much coolant would make a big @ss mess under the hood.

Seems like you'd either have a decent size puddle somewhere or a milky look to your oil.

If you don't see either of those, there's a chance you have a leak in the exh. port.

Ultimately, the heads should probably be pressure checked - that's a more accurate method than having them mag'd.

Does it build pressure before the coolant warms up? We have a cherokee with a 4.0L which is down on power and its blowing oil into the air box so much that its dripping into big puddles. It also builds up pressure in the coolant system even before the coolant is hot.

The oil is dark. That was the first thing I looked for. The heads were pressure tested. And after a couple of valves were lapped, it came back good. But it may have had a bad pressure test at t he shop.

It takes a while to build up pressure, it's not making a mess anywhere. There are no bubbles or foam in the radiator.

It's driving me batty. It will suck the overflow tank dry in 50 miles, but nothing is wet. I've checked the water pump seap holes and shaft seal, they are always dry.

It's like it is evaporating.

Most common place that I've found cracks on SBC's...is above the lifters, on the inside coolant passage wall. If you take the intake off, it would be between the head and the lifters.

Quite often, it cracks in a horizontal line, about 1.5" or so above the lifter bosses.

That type of crack is generally from an overheating condition.

The other type would be a freezing crack - which is generally found on the outside wall of the block. I usually see those not far from the freeze plugs...especially near the motor mount.

Seems like if it was on the outside - you'd have a real obvious puddle under there.

Hope you get this figured out.:flag:

Update:

I pulled the plugs tonight and found a lot of crud. These were clean when I
pulled the heads a week ago. I know, I gapped them.

So engine experts, what does this tell you? That all of the cylinders are now
getting water/coolant? That my (performer) intake has a hole some where?

I still have the original intake I could put on there to see if it is the
intake that is causing the problem.

If I wasn't so subborn and cheap, I would replace the whole engine. But I would
hate to loose what work that the heads and motor have in them. :whine: :banghead:

like gsxmen said. my dads truck would loose coolant and never leave a puddle or make the oil look milky. this went on for severl years. finally the oil started looking milky. pulled the intake and the block was cracked between the lifters and the deck. i had pulled the heads 2 or 3 years earlier and had them checked and never saw the crack. good luck i know its a PITA.

You are definitely trying to burn water from the look of the plugs. Either the block is cracked as GSX said or the intake is leaking. You'll probably find valley under intake full of crud.

It looks to me like the head with the top row of plugs could be warped and you are getting coolant into a few of the cylinders. My guess is that you did not have the heads milled when you had them re-built?

Make sure you check your transmission oil for coolant if you have an automatic with a tranny cooler in your rad. My friend just ruined his transmission cause the rad had coroded out and the coolant was going straight into the tranny. He didnt notice untill it started comming out the vent on the top of the tranny. But it does look like your plugs have been buring coolant. If you are getting lots of coolant in your cylinders you can try to look in the plug holes and see if the tops of the pistons are washed clean, if they are shiny its definately getting alot of coolant into them.

The picture of the plugs was taken after a week of running with a badly
installed and possibly cracked performer intake. I replaced the
performer with the stock intake and the plugs are now running clean.

But I'm still loosing a gallon of coolant every 100 miles. The engine
doesn't smoke or overheat. Actually, it runs fine. There is no coolant
in the engine oil or tanny. There are no external leaks. The cooling
system was pressure checked and held over 10 lbs of pressure over
night.

I've pulled the heads and had them magnafluxed and checked. After
lapping a couple of valves they held pressure. The heads didn't need
surfacing. I reinstalled them with new felpro head gaskets and new
head bolts.

The block is a GM crate engine about 6 years old.
The heads are '69 186 camel hump heads with quite a bit of work.

I'm guessing I have a crack in at least one head that is only opening
up when hot that is allowing coolant into an exhaust port.

Anyone want to sell me a set of good heads? Actually, if someone would
tell me I'm crazy, that would be a relief to me! If I wasn't so cheap
and stubborn, I'd put in a new longblock. But I don't want to loose the
work on the heads if it was not the heads causing the problem.
:banghead: :crazy:

Check your overflow tank real good,could have a hair line crack in it and it opens up when hot coolant gets in there.

Your Crazy....hows that? I think that you would have noticed one of the piston tops being alot cleaner than the rest if you were passing coolant into the combustion chamber. I think that you have a problem elsewhere. Plus if you were burning water, invariably you would end up w/ some in the crankcase because it would wash down the cylinder wall. It only takes a teaspoon or so of water to notice in the oil.

Check around at your local speed shops for a pyrometer or some other type of higher temp meter.

Take a reading of each port (on the manifold - close to the head) and compare readings. If something is out of whack with the readings - you've probably found the offending cylinder(s).

Keep us posted.

have you pressure tested the system. You can rent a pressure tester at autozone "its free" that is how I found my leak.

I say it is your radiator cap.

Have you tried a can of block sealer?? Try it it cant hurt. I am having this same problem with a olds 330 v8 that a friend of mine had built for his father in law. I think that when the valve job was done and they installed news seals that it was drilled out very very close to the water passage. When they pressure test they dont leak but when the piston is more less sucking when on a down stroke it is pulling a small amount of water in at a time. Just my theory though!!

Valve seals shouldn't have anything to do with leaking (they go over the guides). By any chance, did they install hardened exh. seats?

Many times, exh. seats are installed too deep - going into water.

I think he may have meant to say seats instead of seals . I'm just assuming, but from his description of what was performed, that's what it sounds like. Also, Keystroke, no offence intended, but don't waste your money on another set of heads until you find the root of the problem. Another set of heads isn't going to do you much good if your block is cracked. You have a very odd problem and if what you describe is true, I honestly can't even guess where that coolant is going to. Those plugs don't really verify that the lost coolant is being burned. I've done top end jobs on several engines, where the head (or sometimes aluminum intakes) warped, cracked or corroded, allowing coolant into the combustion chamber and without fail, the spark plugs (along with the piston tops) were washed damn near spotless. At the rate you're going through coolant, your plugs would be washed, not dirty. The coolant has to be going somewheres. Didn't somebody, earlier in the thread, suggest coolant dye to trace where the missing coolant is ending up? That may be a very good suggestion, at this point.