Talk Morgan Forums Morgan Sports Cars Maintenance & Servicing PCV Valve question and dipstick oil leak

So I've been getting a fair amount of oil bubbling up from the oil dipstick hole on my TR4 powered 1965 Plus 4. In fact, if I fill the oil to the top line on the dipstick - it will leak from the dipstick hole severely until it settles at the half way point. However, oil will continue to slowly leak through the dipstick hole down to below the low mark if I let it - just more slowly.

I put some oil leak dye in - and I really don't think it is the front or rear main seal. The timing chain cover is pretty dry at the bottom. There is a puddle of oil on the "shelf" where the dipstick hole is, and the oil pan itself is covered in oil - primarily on the left side (the side where the dipstick is). There is not a lot of oozing from the bell housing - but the oil on the oil pan does eventually make it's way rearward - but most of it sits covering the left side of the oil pan - I assume it is dripping down from the dipstick hole.

So my first solution was to buy a rubber cork, drill a hole in it, and seal up the dipstick hole (I know there should be a felt washer on the dipstick - but the oil leak would easily overwhelm the felt).

I imagine the oil pan gasket could be the culprit as well...but I really think the dipstick is the source based on the dye distribution and the fact that the oil leak is most serious when filled to the top line.

The question is - why is this happening? The TR4a motor cannot have been engineered to leak this much oil through the dipstick! I have noticed that my car (newly bought by me) does not have a PCV (Positive Crankcase Ventilation) valve of the right side of the engine. It does have a large vented, black "slip on" oil cap on the valve cover which appears to be vented on the bottom.

When I run the the car without the oil cap on, I note that air is NOT sucked into the motor from the oil fill port on the valve cover - rather it blows out of the region of the oil cap.

Did 1965 Plus 4's have PCV valves installed? (I believe TR4's did)

Should I install a PCV valve?

Is there another solution/cause of this oil leak?

Should I stop worrying and just revel in my [ genius ] solution of using a rubber cork around the dipstick?

Any advice appreciated...

If you seal the dipstick hole the oil may find an alternative route out.

Is this pressurised oil or splash? Is it the correct dipstick for that engine?

My '67 Midget had an early PCV valve which comprised a small metal pancake assembly on top of the manifold between the carbs. Inside was a rubber diaphragm. The hose from this went direct to the crankcase breatherlocated on one of the tappet chest covers. So by 1967 this was being done.

Images on line show a hose from the rocker cover which splits at a Y piece and each hose goes into the air filters.

You maybe need to talk to a TR4 engine expert. Try the TR Clubs?

I *think* that oil is blowing out of the dipstick hole - that would suggest a blocked engine venting system...

My car does not have any breather tube on the valve cover - but it does have a vented oil cap: Vented Oil Cap from Moss Website

It seems to me that the vented cap should be sufficient to vent the block and prevent oil blowing out the dipstick hole - no?

I'll take a look at the cap tonight - perhaps the vent has somehow been blocked?

Sounds as though there is pressure in the crankcase. Are you able to check the compression in each cylinder? If you're getting enough pressure to force the oil up the dipstick hole you may have blow by in one cylinder.

I changed the OE rocker oil breather cap with one having a pipe union on my diesel Land Rover. The short rubber pipe from same routes into a union on inlet pipe between air cleaner and manifold to suck in oil fumes. This cured heavy breathing from the engine which previously coated rocker cover with oil film.

Maybe something similar would work for you.

With an old engine chances may be that either the bores and/or piston rings might be a tad worn causing an increase in pressure within the crankcase, which is in no way unusual, perhaps even less so for a rarely used vehicle..? In times past the norm was to just vent the crankcase to atmosphere. As Dave suggested in time the vent was redirected into the air filter housing, in order that the vented fumes would burn in the combustion chambers..A worn engine would generally foul up the air filter with oil mist at the point where the vent tube entered the air box...

From a very dull memory early TR`s may have had a wire mesh filter built into the oil filler cap on the rocker cover, which if full of crud could be washed out in a bath of paraffin or similar.

If your engine might be a tad worn and uses a little oil in your usual/expected mileage, then perhaps a breather could be directed to an aftermarket oil catch can to keep the engine a bit cleaner...?

My car has a vented oil cap that looks like this,
Shouldn't that be enough to vent the crankcase? I'll check and see if it's gummed up...could be...

If it's high mileage, I'd do a quick compression test

You could also connect a clear tube to the dipstick hole and see if it blows bubbles in a test jar of liquid ?

In the last 18 months, I've built two TR engines so I'm speaking from actual hands on experience.

TR4A had the PCV but not the TR4 or earlier models. Manifold should have 37544 cast into it

The earlier models had a breather which is on the left hand side of the block - a sort of convoluted piece of 1" steel tubing.

Just check to see that is as clear as it can be

My other thought is that the oil pressure relief valve has stuck, a common occurrence on a TR engine causing the oil pressure to rise. What sort of reading are you getting on the guage. You should be getting no more than 65/75 psi at 2000 rpm. Not that I'd believe the gauge though so a master gauge is a good idea.

Arwyn

Hope it’s permissible to do this, but I have lifted this thread from the TR register forum, which may help to reinforce Arwyn’s advice:

“Crankcase breathing ex-factory was not entirely satisfactory.

TR4s followed TR3s design, having a breather pipe in the

block, beside/just below the fuel pump.



TR4As had this provision in the block blanked off and made

provision for venting the rocker cover (2 or more arrangements).



Now, you seem to have the original TR4 rocker cover (without

breathing - correct for TR4) but has the blanking plug (originally

fitted to TR4As) been removed and replaced with a TR3/TR4

style breather pipe?



If not, then you will have a build-up of pressure leading to many

oil leaks.”