Leaking intake gasket caused by too much blow-by?

[Killick]

Hi Everyone,

I've got a 10 year old Vetus (Mitsubishi) diesel in my sailboat. Boat is new to me, the engine has less than 400 hours. It ran great, so far..until yesterday when I noticed the smell of exhaust in the engine compartment. Took a look and it appears to be leaking exhaust out of the intake gasket. Bit of black soot near where the leak is.

Now, when starting the motor, there's a distinct "air sound" before it actually fired up. There's a blow-by hose that goes from the cover to the intake manifold (near where I think the leak is), if I take put my finger over the end of the hose with the engine running, within a few seconds I can feel the pressure building up. What's normal? No smoke just pressure.

This seems to be a sudden thing, it's been running well, with no sign of trouble before yesterday. Since the engine is new to me, I've been constantly checking the oil, looking for potential issues, adjusting idle speed ect, and noticed nothing until the leak happened.

Could the pressure from the vent hose have blown the intake gasket? Attached to the intake manifold is the air intake so there shouldnt be any pressure there, correct? Could I just have an old gasket that needs replacing, or more serious issues.

[DieselDavy]

Welcome Killick!
I am going to be of no value to you here (on this subject) except that maybe my welcome will bump the subject back to the top and maybe someone else will see it and have some advice.
This really is a great site for GM diesel info...

dave

[More Power]

Hi Everyone,

I've got a 10 year old Vetus (Mitsubishi) diesel in my sailboat. Boat is new to me, the engine has less than 400 hours. It ran great, so far..until yesterday when I noticed the smell of exhaust in the engine compartment. Took a look and it appears to be leaking exhaust out of the intake gasket. Bit of black soot near where the leak is.

Now, when starting the motor, there's a distinct "air sound" before it actually fired up. There's a blow-by hose that goes from the cover to the intake manifold (near where I think the leak is), if I take put my finger over the end of the hose with the engine running, within a few seconds I can feel the pressure building up. What's normal? No smoke just pressure.

This seems to be a sudden thing, it's been running well, with no sign of trouble before yesterday. Since the engine is new to me, I've been constantly checking the oil, looking for potential issues, adjusting idle speed ect, and noticed nothing until the leak happened.

Could the pressure from the vent hose have blown the intake gasket? Attached to the intake manifold is the air intake so there shouldnt be any pressure there, correct? Could I just have an old gasket that needs replacing, or more serious issues.

Welcome to the board!

All engines, whether gas or diesel or new or old, will produce some amount of blow-by past the piston rings. So, it would be normal for some pressure to develop in the crankcase vent hose if you held your finger over it. In a diesel engine, a "bad" amount of blow-by is usually accompanied by a fair amount of white vapors, which is unburnt fuel, and a miss in a particular cylinder due to a damaged piston or rings.

Don't suspect a more serious problem until you've eliminated the easy and less expensive possibilities. It could be that a gasket has begun leaking.

Does the engine run smoothly? Does it produce normal power? Does it start normally?

Jim

[Killick]

Thanks Guys,

I'm going out to the boat today to replace the intake manifold gasket. I'll report back!

[rustyk]

It could be a sticky or bad intake valve. The new intake manifold gasket likely won't help if that's the case.

[Killick]

Just a follow up.

Went to the boat, ran the engine and could feel pressure & exhaust coming from the intake manifold gasket. Replaced the gasket, didn't change a thing. Checked exhaust mixer elbow, clean. Running the engine again, feeling more carefully, found an injector near intake manifold was leaking. Took the injector out, found carbon gunk at the bottom where it seats on a copper ring. I cleaned up the carbon as best I could and put it all back together..runs fine. I had no idea an injector could leak like that.

[rustyk]

Great! What you encountered is likely fuel being splattered and burning past the exhaust stroke to the intake stroke, and so the combustion is still going when the intake valve opens.