Oil cap hissing noise

jluis

jluis

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1,703
I noticed on my 3200 that while the engine is running there's a hissing sound on the oil cap and it's pulling a vacuum due to the oil separator/breather connected to the intake manifold.
I never paid attention if this is normal or not, so before buying a new oil separator can some 3200 owners tell me if this is normal or not? The cap is intentionally drilled to vent the engine ..
 
Oneball

Oneball

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11,125
I’ve never seen inside a 3200 separator but they are usually just a baffled tank, there’s not a PCV in there.

Have you lost the o rings off the cap?

Put up a photo of your cap. I don’t think mine had a hole in it.
 
jluis

jluis

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1,703
It’s not the rings, it’s the hole on the side. If I put my finger in it I can feel the vacuum and the hissing stops.

Maybe it always did that and I never paid attention …
Can you please check yours the next time you start it?
 

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Oneball

Oneball

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jluis said:
I wonder why …
Car only had 1 owner from new and was serviced at the dealer.
Engine was replaced under warranty due to end float. I wonder if that’s Maserati solution for the end float problem :)
Click to expand...
Seriously doubt it. I’d have a look and check the rest of the oil breather system is as it should be.

But pretty much every car for the last 40 years has used a closed circuit system linked to manifold vacuum. None that I can think of have a vented oil cap. I won’t run properly like that.

Get the epoxy out!
 
jluis

jluis

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1,703
Oneball said:
Seriously doubt it. I’d have a look and check the rest of the oil breather system is as it should be.

But pretty much every car for the last 40 years has used a closed circuit system linked to manifold vacuum. None that I can think of have a vented oil cap. I won’t run properly like that.

Get the epoxy out!
Click to expand...
I know, it was a joke.
Yep, a bit of epoxy or aluminum tape around the holes …

The rest of the breathing system seems to be correct, I just need to check if the one way valves are sealing correctly or not.
This is the second problem I see on the intake manifold vacuum system.
The first one was a faulty Siemens valve causing the car to suck in the gas from the evap tank at all times making it sometimes stall when starting.
 
allandwf

allandwf

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10,995
I've looked further, it goes all the way through and appears to have a cotter pin fitted, presumably to stop the dip stick dropping into the sump as it is a flexible type.
 

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Frog3200

Frog3200

Junior Member
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53
2 holes exactly opposite seems normal. but I don't think they vent and yours has been drilled in the inside as well. It is possibly a solution to avoid a different hissing sound. I put a coin that if you block theese holes you will have a hissing sound (but different) at idle when hot.

If yes, then (according to 3200 science gathered here and there...) : it's because the vacuum created at idle is too important, creating a hissing sound that supposedly comes from the crankshaft gasket as the vacuum takes the thin oil film a bit away.. Quite scary. The solution (or one solution) is to limit or block the vacuum at the one way valve in copper going from the seperator to the intake. According to some readings, some Maserati techs did that in germany with a little screw in the one way valve, others (like me and other owners in France) did it with a part of a rivet in order to keep a vacuum but reduced.

If I'm right then the holes in your cap would be a different solution to this problem. But IMHO it is not the best as exterior air in the crankcase bring also humidity, water...

You may want to take a look at this topic. I tried to make a "research" on the crankcase ventilation, there are some mistakes, but you can see the rivet photo..

 
jluis

jluis

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1,703
Frog3200 said:
2 holes exactly opposite seems normal. but I don't think they vent and yours has been drilled in the inside as well. It is possibly a solution to avoid a different hissing sound. I put a coin that if you block theese holes you will have a hissing sound (but different) at idle when hot.

If yes, then (according to 3200 science gathered here and there...) : it's because the vacuum created at idle is too important, creating a hissing sound that supposedly comes from the crankshaft gasket as the vacuum takes the thin oil film a bit away.. Quite scary. The solution (or one solution) is to limit or block the vacuum at the one way valve in copper going from the seperator to the intake. According to some readings, some Maserati techs did that in germany with a little screw in the one way valve, others (like me and other owners in France) did it with a part of a rivet in order to keep a vacuum but reduced.

If I'm right then the holes in your cap would be a different solution to this problem. But IMHO it is not the best as exterior air in the crankcase bring also humidity, water...

You may want to take a look at this topic. I tried to make a "research" on the crankcase ventilation, there are some mistakes, but you can see the rivet photo..

Click to expand...
Ah the joys of owning these temperamental cars …
Thanks for the pointer, I had considered reducing or blocking completely the vacuum from the intake as the system would still be able to correctly vent via the outlet to the air filter box
 
Frog3200

Frog3200

Junior Member
Messages
53
Exactly. Some did that too. If ever you decide to go for the rivet solution, you have to pinch it a bit to reduce. Remember it's highly scientific:yeah:
 
Oneball

Oneball

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11,125
jluis said:
Ah the joys of owning these temperamental cars …
Thanks for the pointer, I had considered reducing or blocking completely the vacuum from the intake as the system would still be able to correctly vent via the outlet to the air filter box
Click to expand...
Don’t block the vac pipe as there’s a one way valve in the breather pipe so you’ll have a build of of crankcase pressure. The crankcase breathes into the manifold from the air filter not the other way round.

Having holes in the oil cap will let unmetered air into the intake so it won’t run corrrctly.
 
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