1990 7.4 loosing Anti-freeze, milkshake oil, comp test & leak down done.

Navman

Cadet
Joined
Oct 30, 2018
Messages
8
Long time learner from this site, first time poster!

Loosing a quart of anti-freeze after 10 hours of running, milk shake oil

Past 15 years always ran 5 gallons of pink anti-freeze thru it at operating temp before storing next to the house in Oregon.

Getting harder to get on plane over the last several years, top end & mpg remained the same on 1991 3055 Bayliner

Removed radiator cap during warm up for leak down test, slow warm stream flowing then all of a sudden the level starts rising fast, got the cap back on before losing much coolant.

Brought Engine up to temp and radiator level was normal again, flowing fast with No bubbles.

No bubbles at all during the leak down test either.

Didn't go outside of boat to listen for exhaust leaks at transom.

Since no bubbles, wondering if it's the intake manifold gasket leaking?

Would you guys & girls look over this and give me your thoughts please?

Thank you!

Mel



1990 Mercruiser 7.4 Ser. OD433606 Mod. 474B11OCS 860 hours

Compression Test - engine Cold

Leak Down test - engine Warm




Cyl. Cyl.

1 - 125 psi, leak down 2 % valve covers. 2 – 120 psi, leak down 31 % valve covers

3 – 110 psi, leak down 40 % VC & Carb. 4 – 90 psi, leak down 72% VC & Carb

5 – 87 psi, leak down 77 % VC & Carb. 6 – 100 psi, leak down 62 % VC & Carb

7 – 120 psi, leak down 8 % VC only. 8 – 120 psi, leak down 10 % VC & Carb
 
Last edited:

alldodge

Moderator
Staff member
Joined
Mar 8, 2009
Messages
40,582
My guess is a head gasket leak, and with that much loss in the leak down test, should do a head refresh anyway. The 860 hours is getting up there, but seams you have been taking care of it, so having a look can verify
 

tpenfield

Moderator
Staff member
Joined
Jul 18, 2011
Messages
17,621
Your leak down numbers are a horror show, compression numbers are not all that great either. . . , but it may not have anything to do with the milky oil.

i am assuming that you have closed cooling. Leaving the heat exchanger cap off while running will get you a coolant eruption as you described, because there is no pressure in the system.

since you have closed cooling, you can do a cooling system leak test. There should be none.

Have you checked / changed the exhaust manifold gaskets lately?

Do the cooling system pressure test ( drain it down and listen for the air while you put about 10-15 psi into the system). Then see where that leads.
 

Navman

Cadet
Joined
Oct 30, 2018
Messages
8
My guess is a head gasket leak, and with that much loss in the leak down test, should do a head refresh anyway. The 860 hours is getting up there, but seams you have been taking care of it, so having a look can verify

Thanks AllDodge!
I thought Head Gasket too, but the lack of bubbles in the heat exchanger threw me off...
 

aimlow

Petty Officer 2nd Class
Joined
Nov 7, 2018
Messages
180
Ever hydrolock? Does GM use those crappy silicon intake manifold gaskets on a big block? Plugs wet with water?

Water inside a cylinder seldom gets into the oil on a running engine. More likely a cracked head/block., or leaky oil cooler.
 

Navman

Cadet
Joined
Oct 30, 2018
Messages
8
Your leak down numbers are a horror show, compression numbers are not all that great either. . . , but it may not have anything to do with the milky oil.

i am assuming that you have closed cooling. Leaving the heat exchanger cap off while running will get you a coolant eruption as you described, because there is no pressure in the system.

since you have closed cooling, you can do a cooling system leak test. There should be none.

Have you checked / changed the exhaust manifold gaskets lately?

Do the cooling system pressure test ( drain it down and listen for the air while you put about 10-15 psi into the system). Then see where that leads.

"Horror Show" Thanks Ted lol

Yes, closed cooling

When you say "drain down the coolant" do you mean all of it (so maybe I don't force coolant into the Cylinders)?

I put new Barr Exhaust, Risers, Elbows & gaskets on April 2007.

Fresh water use only
 

tpenfield

Moderator
Staff member
Joined
Jul 18, 2011
Messages
17,621
"Horror Show" Thanks Ted lol

Yes, closed cooling

When you say "drain down the coolant" do you mean all of it (so maybe I don't force coolant into the Cylinders)?

I put new Barr Exhaust, Risers, Elbows & gaskets on April 2007.

Fresh water use only

Yes, all of it. You want to test the closed cooling system for leaks, and air leaking is much easier to detect than a liquid.

The milky oil could be either failed exhaust manifold gaskets (which your leak test numbers seem to indicate, given that the 'middle' cylinders (3,5,4,6) have high leak. . . . or the milky oil could be from a cracked engine block. Since you have closed cooling, it is straight forward to test the cooling system for any cracks in the block.

Is it a FULL closed cooling system (block & exhaust manifolds) or a HALF system (block only)?
 

Navman

Cadet
Joined
Oct 30, 2018
Messages
8
Yes, all of it. You want to test the closed cooling system for leaks, and air leaking is much easier to detect than a liquid.

The milky oil could be either failed exhaust manifold gaskets (which your leak test numbers seem to indicate, given that the 'middle' cylinders (3,5,4,6) have high leak. . . . or the milky oil could be from a cracked engine block. Since you have closed cooling, it is straight forward to test the cooling system for any cracks in the block.

Is it a FULL closed cooling system (block & exhaust manifolds) or a HALF system (block only)?

Yes Ted it's a Full closed system block & exhaust manifolds.

Good catch on the middle cylinders! I've been cramming so much to learn all of this I missed that
 

Navman

Cadet
Joined
Oct 30, 2018
Messages
8
I may have to get my Wife to listen, she has ears like a Bat.. :D

We have the same engine and I really enjoyed the documentation & photos of your rebuild
 
Last edited:

aimlow

Petty Officer 2nd Class
Joined
Nov 7, 2018
Messages
180
A head gasket performs a few functions. It seals compression (the fire rings around a cylinder) and it seals water, oil, a pushrod passages. The most common failure is a fire ring, but the pressure of compression/ignition for surpasses the pressure of the cooling system, a seldom will coolant leak into a cylinder on a running engine. Bottom line..water in oil is not usually a head gasket issue!
 

Navman

Cadet
Joined
Oct 30, 2018
Messages
8
A head gasket performs a few functions. It seals compression (the fire rings around a cylinder) and it seals water, oil, a pushrod passages. The most common failure is a fire ring, but the pressure of compression/ignition for surpasses the pressure of the cooling system, a seldom will coolant leak into a cylinder on a running engine. Bottom line..water in oil is not usually a head gasket issue!

Well that's encouraging aimlow

I think the next step is to pull exhaust manifold, risers & elbows then pressure test coolant system like Ted was suggestion
Fingers crossed!
 

tpenfield

Moderator
Staff member
Joined
Jul 18, 2011
Messages
17,621
Since you have a full closed cooling system, Pressure test it before you take the exhaust manifolds/risers/elbows apart.
 

Navman

Cadet
Joined
Oct 30, 2018
Messages
8
Since you have a full closed cooling system, Pressure test it before you take the exhaust manifolds/risers/elbows apart.

I had it backwards Ted thinking with the exhaust system removed it could hear head gasket leakage

But your right, wouldn't tell me anything about exhaust/gasket leakage

It's been 30 years since i changed my own oil let alone digging into an engine like I did in my younger days.

I really do appreciate your help
 

alldodge

Moderator
Staff member
Joined
Mar 8, 2009
Messages
40,582
Never seen a head gasket seal push rods, not saying they don't but not on a BBC. Gasket will seal the water jacket and while running any that make it into the chamber will be expelled. After the motor stops it can leak into the cylinder and down past the rings.

You mentioned that there was coolant in the oil and that the coolant rushed up fast and started over flowing with the cap removed. This can happen from combustion pressure being pushed into water jacket past the head gasket. Not saying this is your issue and doing a pressure check as Ted posted would be a good first check.

If its a small leak then it may only show up once motor reaches operating temp
 

aimlow

Petty Officer 2nd Class
Joined
Nov 7, 2018
Messages
180
Water has a very high surface film strength and is not very "missive", meaning it won't get as thin as a petroleum product to leak past ring lands and ring end gaps. This is the main reason why you don't use water to determine cylinder heads volumes. If there is any oil present on the cylinder walls, water usually sits on top of the pistons and rusts the cylinder walls.
 

Navman

Cadet
Joined
Oct 30, 2018
Messages
8
After the initial surge of anti-freeze in the heat exchanger fill cap, I never saw one bubble go by with the cap off.

Thanks guys!

Mel
 
Top