350 motor intake manifold leak?

[81vee]

Hey there guys,

I've been recently working on a project left off by my dad on an 81 chevy k20, and i've been trying to sort out what on earth happened to the brand new small black 350 crate motor with an aluminum intake that he put in it. Coolant has been mixing with the oil, no doubt, as the oil looks almost like a milkshake; really bad.

Water isnt gushing out of the motor when it runs, and pressure in the radiator is normal. It holds pressure, and when it runs it keeps at 15-16 psi, and then later drops down to about 2-3 psi when the thermostat opens. Not sure if the last part is normal. 

If you fill the radiator in the evening and you come back in the morning, the coolant is lower than what i filled it too.

When the motor runs, coolant is obviously going somewhere. The level goes right down.

I just took off the intake manifold today, and the gasket is still very much fresh. The aluminum manifold will be checked if it is warped with a mechanics's ruler and feeler gauges tomorrow. I want to note that the bolts holding it on were quite easy to take off, and had rust on it. Probably too easy. All of the passages leading to the valves seemed fine except for the third one in on the right side, if you were to look from the front of the engine. It seems to have some rust on the passage, and the valve looks decent, but not mint. The rest of the block seems to be okay.

I've been scratching my head over this. I'm really unsure what's going on over here. The gasket seemed to hold, there's not really any evidence of water tunneling through it. Maybe you guys can help?

Thanks,
81vee

[bd]

Welcome to the site from Central California!

First, some basics.  The left (driver) side of the engine is the odd numbered cylinder bank with cylinder number 1 at front - so cylinders 1-3-5-7 are on the left, numbered front to rear.  The even numbered cylinders are on the right (passenger) side with cylinder number 2 at front.

If you pull the spark plugs and keep them in order by cylinder, are any wet with coolant or do any appear to have especially clean electrodes and insulator as though they've been steam cleaned?  With the engine cool and the cooling system full, pressurize the cooling system to 20 PSI and let it sit overnight.  What's the residual pressure in the morning?  Is there any coolant on the ground under the vehicle or signs of external coolant leakage from hose connections, radiator, the four corners of the intake manifold, water pump weep hole, welch plugs, etc?  With the spark plugs still removed, have an assistant crank the engine over while you watch under the hood from in front of the radiator - do not hang your head over either fender in case fluid is forcefully expelled from the engine while cranking.  Did any moisture blow out of a spark plug hole on the initial crank?  Which cylinder(s)?  Have you run a compression test or cylinder leak down test?  What were the readings?  With the spark plugs installed and cooling system full, install the radiator pressure tester on the radiator neck.  DO NOT pump up any pressure.  Instead, start the engine and let it run to temperature while you monitor the pressure gauge.  How long does it take for pressure to climb to 15 PSI?  Does it continue to climb toward 20 PSI?  To avoid rupture, never let the cooling system build pressure beyond 20 PSI.

Coolant could be leaking internally past the intake gaskets into the valley from the coolant passages located at the front and rear of the cylinder heads, especially since you mentioned that the intake bolts were loose.  But, moisture in the intake runner is also troubling.  Initially, try to determine whether any coolant is entering the combustion chambers or simply dumping directly into the lube system.  The sudden drop in cooling system pressure when the thermostat opens implies there maybe air trapped in the cooling system.  The steps listed above should help you better isolate the source(s) of the coolant loss and possible solutions.

[81vee]

Thanks for the helpful post 

To add more information, I took the spark plug out of the number 5 cylinder, and it was quite clear that water was getting into the cylinder. Even though the engine has been sitting with no water and oil for a while, it was still wet and was actually partially rusted to the side of the block, making it really hard to break free. It did not seem clean at all, to be honest. It could also be because when the spark plug was taken out, it was dropped into oily speedy dry
 -_-
 Even with that, it seemed too wet and dirty to be "steam cleaned" as you've said.

A while back, my dad's friend, who's been a mechanic since Vietnam (not kidding, he was in the war), did a series of tests and I recall him telling me that it held pressure. However, I also renember that it went down slightly when I did it myself from sitting overnight, but there was not a drop of anything on the ground. There was some splatter on the manifold, but that was most likely from when we let the radiator burp. In all the tests me and the mechanic have done, there hasn't been an excessive buildup of pressure on the radiator. Oil pressure is unknown as a previous owner never put a sensor on it, and wiring issues are preventing me from putting in a new gage and sensor.

Since we have the intake manifold and gaskets off, we can't really run the engine again. Right now, me and the mechanic, who is helping me, are going more invasive. I'll see if I can send some pictures later today.

Thanks,
81vee

[Rattler12]

I had the same milkshake problem with a 305. Check out the heads and the water passages front and back looking at the thickness of the sealing surface to the manifold. On one of mine the surface had corroded enough that there was just a little more than 1/16 inch in one lower corner for the gasket to seal against. Water was getting by the gasket, running to the back of the block and down into the pan. Local machine shop welded some material in, resurfaced the intake surface and viola.....no more milkshake.

[81vee]

Alright, pictures can't be done. No matter what I do, the image is always over 500 kilobytes.

We decided to go right ahead and change the intake manifold gasket. We decided that water ran behind the gasket due to it not sealing correctly. We also discovered some nasty pits on both the block and the manifold. These off brand motors and heads are made of cheap crap. The "aluminum" intake already has rust on the water jackets.

We put some nice red thermal gasket sealer with the new gasket, and made sure to put enough to fill the pits. Apparently they weren't bad enough to be machined, so I guess I'm going to fire it up tomorrow and pray it works.

Cheers,
81vee

[75gmck25]

Did you buy the recommended gasket for your aluminum intake manifold?   Edelbrock (and others) have very specific recommendations for which Fel Pro gasket to use, and they warn you that you can't use the stock gasket for an iron manifold and get it to seal properly.

Bruce

[81vee]

I bought the specific gasket I needed, even though it seemed like it was exactly the same as the old one on there.

However, now that I've put the manifold back on with proper torque, I have some confidence that my troubles have been remedied. Those bolts I took off were definitely not torqued, which is why I think it failed. I snugged everything down to 25 foot lbs, and I reconnected almost everything. I just have to set the distributor in. It seems like the till in the block moved on me when I was doing the job, so ill turn it so I have the timing right. I even tightened the heads back to spec, just because I was doing all that work anyways. 70 foot lbs for those. I also decided to change the spark plugs. The guy who installed this painted over them.

I should be able to fill er up with water and oil tomorrow. It took too long to get everything situated :T

-81 vee

[bd]

Retorque the intake bolts in the morning and then again in one to two weeks.

[81vee]

Noted.
Thanks again for the help.

Tomorrow is when we are going to do the timing for the distributor. I'd also like to mention that the number five cylinder was blowing oil out of it. I don't like that very much, buy it could be old gunk stuck from last time.

I'm also going to be seeing if I can't fix the hot terminal trouble I've been having. I think it's the shot ground wire, so I'll replace that, and then rebuild the starter if I have to.

[81vee]

Alright. I guess it's been a while. Time to update.

Intake manifold seemed to hold. No leaks anywhere. Engine started fine, nothing to note. Need to adjust the A:F mix, and make sure the timing is good.

Oil is discolored, but the level hasn't changed, so i'm assuming it picked up all of the cream shake that was left in it.

So, I guess it's okay for now. Haven't been able to drive it because I have to bleed the brakes. Should be fun.

I have one other major issue, but it doesn't have to do with the manifold. The steering has much play in it, as in you can do about a half of turn before the wheels budge. But that's for another post.

Tanks for your help.

-81vee