Seriously?

[Laird Scooby]

Originally Posted by foggyjames

Surely breathers have nothing to do with oil pressure...? Crankcase pressure, yes, of course, but not oil pressure!

cheers

James

That's probably why they weren't attended to when the carbs were rebuilt and why they're now giving a problem.

On the Rover V8 (aka POB215/Buick Special) engine, they certainly do have an effect on oil pressure, not forgetting performance and fuel economy too.
I've had several Rover V8s in my time and all had blocked breathers when i first got them.

Don't forget though, if the crankcase pressure goes up, the pressure into the oil pump will go up and therefore the pressure out of the pump as well. Perfectly logical when you think of it that way.

[foggyjames]

I wouldn't dispute the virtues of a crankcase ventilation service for a moment - just the link to oil pressure! I'd have thought you'd have to have horrendous blow-by to raise the crankcase pressure enough to affect the oil pressure when the engine is un-loaded, such that crankcase ventilation will be the least of your worries! Maybe, maybe wide-open at high RPM, but I'm really struggling to see it happening close to idle.

I don't know what the oil pressure specs for an RV8 ought to be, but the Redblock I have an oil pressure gauge on never drops below 3 Bar (~45psi), even at idle when roasting hot. Could this not just be a particularly healthy one?

Anyway...it may well need a crankcase ventilation service, it just struck me as a bit damning to condemn it as lashed up based on an oil pressure reading!

cheers

James

[Laird Scooby]

Originally Posted by foggyjames

I wouldn't dispute the virtues of a crankcase ventilation service for a moment - just the link to oil pressure! I'd have thought you'd have to have horrendous blow-by to raise the crankcase pressure enough to affect the oil pressure when the engine is un-loaded, such that crankcase ventilation will be the least of your worries! Maybe, maybe wide-open at high RPM, but I'm really struggling to see it happening close to idle.

I don't know what the oil pressure specs for an RV8 ought to be, but the Redblock I have an oil pressure gauge on never drops below 3 Bar (~45psi), even at idle when roasting hot. Could this not just be a particularly healthy one?

Anyway...it may well need a crankcase ventilation service, it just struck me as a bit damning to condemn it as lashed up based on an oil pressure reading!

cheers

James

A particularly healthy V8 will NOT show in excess of 45 psi at idle as this one appears to show. It is well known in Rover circles that the oil pressure should only be 35psi hot at 2000rpm or above or it will blow oil seals.

The Rover V8 engine uses what is essentially a "sealed" PCV system except for the Y shaped feed from the rocker cover to the carbs. Usually they block up on the carb stubs and that is when crankcase pressure builds, no need for blow-by to create it!

The redblock is a completely different animal and yours appears to be normal for a redblock. Horses for courses as it were.

[foggyjames]

I can well imagine that oil pressures in that range could cause leaks - sealing technology has come on a long way! I suspect I have fun ahead getting my B30 to remain oil-tight! In the interests of cordiality I'm going to bow to your greater familiarity with these engines when it comes to the cause, but I do remain a little sceptical!

Out of interest, do the oil pumps have a pressure relief / over-pressure valve?

cheers

James

[Laird Scooby]

Originally Posted by foggyjames

I can well imagine that oil pressures in that range could cause leaks - sealing technology has come on a long way! I suspect I have fun ahead getting my B30 to remain oil-tight! In the interests of cordiality I'm going to bow to your greater familiarity with these engines when it comes to the cause, but I do remain a little sceptical!

Out of interest, do the oil pumps have a pressure relief / over-pressure valve?

cheers

James

I understand your scepticism, i was also sceptical when i was first told this ~35 years ago. It is right though.

There is an oil pressure relief valve, yes. From memory it's set to open at 65psi but i may be wrong on that. Also many of the later, larger engine models (3.9 upwards) if they overheated they could cause the oil pressure relief valve spring to go weak, causing it to open much too early like ~6psi which isn't enough to protect the engine - you can guess the end result!

Also many moons ago i ran a series of Mk2 Cavaliers, all 1600 and they shared a problem with the oil pressure relief valve spring going weak. This showed as the oil pressure light flickering at idle even when cold and barely 2bar of pressure hot and running (2000rpm or higher) according to factory fitted gauges.
The spring was ~£3 at the time, took about 5 minutes to fit and cured it instantly.