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MG MGB GT V8 Factory Originals Technical - Bad breathing

My breather pipes keep clogging up with lightish yellow/cream gunge. Cleaned out the pipes and flame traps and after 1000 miles they are clogged again.
I have pipes coming from both rocker covers, joining and then into the air cleaner.
Advice would be appreciated.
Mark Rawlins

This happens when your trips don't last long enough to evaporate condensation, will also cause silencer to fail prematurely. Move farther from work, maybe?
George B.

How does air enter the engine? Try a small air filter on one rocker box and route the breather from one flame trap to the air cleaner.
Is the engine at normal temperature? Although cool running of the V8 not usually a problem.
Do you have a coolant leak?
Geoff King

I think you have a coolant leak..(head gasket)I use my BV8 all weathers with short town trips etc. with no adverse effects.

Maybe try a coolant system pressurisation check.Or park it up, forget about it till the spring and go to the pub!!....hic

Mark, I hate to add to bad news but I fear John above is spto on ; sounds like the dreaded "making mayonaisse" tells of a coolant leak mixing with the oil thus producing the sludge appearing in the cap and pipes. Short runs should have no adverse consequences.
In addition to the pressure check a vacuum gauge test and compression test should tell what and where the source lies. Pete, Sydney, Australia
Peter Thomas

Thanks to all.
Its a bit of a mystery, I dont normally do short journeys so I dont think thats it.
There are no obvious signs of a head gasket leak as the system is not pressurising. Anyway I have recently had the heads off and it was the same before.
The oil on the dipstick seems OK.

Geoff, I tried a filter on one of the rocker covers and drawing from the other into the airfilter. Rather than suck air in, fumes were coming out of the filter.
I have a late 4.0L engine and apparently you dont need to let air in!

I will change the oil and see if that helps.



Mark Rawlins


This is a sign that the engine oil isn't getting hot enough.

Optimum temp prob 100-110deg C.

Are you using an oil cooler? Whats the water temp like?



I have a Factory V8 temp guage and it does seem to run cool with the needle pointing to 7 oclock when on the move.
I could try covering the oil cooler to see if things improve.
Thanks for the input seems to make sense.

Mark Rawlins


Sounds to me like the engine simply isnít breathing. With both rocker covers connected together there will be no air flow apart from the piston blow by and whatever can be sucked in around the dip stick tube. If you fitted an air filter to one rocker cover, connected the flame trap to the air cleaner and fumes came out of the filter it still isnít breathing but the crankcase is pressurising.

What happens when you remove the oil filler cap with the engine running, do you get fumes coming out or air going in?

I would go back to one rocker cover vented from the flame trap to the air cleaner (downstream of the element) and a filter on the other cover for air to get in. The vacuum downstream of the filter element should be enough to maintain a flow of air through the engine.

I donít know what Rover did with the later engines but surely they still need to breathe?

Geoff King


From your description it sounds like you have the early rocker covers (like standard MGB GT V8) on a later 4.0 engine. I thought that the early engine had breather filter(s) to let air in at the back of the block and both rocker covers vented the flame trap by pipes, whereas the later 4.0 engine simply has a small breather filter at the rear of the left rocker cover and a flame trap at the front of the right. If my recollection is right then its sound like Geoff King is right .. the combination of early and late parts means there is no where for breathing air to get in !

Geoff Richmond

I will put the breather filter back on, clean up the pipes and connect up the other side to the air filter base and run it for a while to see if there is an improvement.
I have been using the factory V8 flame traps are these OK. (new)
Car is off the road for a week or two due to suspension/steering mods.

Thanks for the help.

Mark Rawlins

This thread was discussed between 14/11/2001 and 18/11/2001

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