removing oil cap whilst engine is running

dada44

Hi there,

Have a vw polo for sale. 7 years old.

Had a buyer come round to see it, and with the engine running, he removed the oil cap on the engine.

As soon as he did this the engine started whirring and wheezing. He did this a couple of times and pointed out that something might be wrong with the engine?

Q. Could he have caused any damage to the engine?
And was he right?

LandyAndy

No..
Yes..

hartcjhart

depends
no,
no,

Strider590

LandyAndy wrote: »

No..
Yes..

:rotfl:



Something to do with with air pressure inside the engine while it's running, im not sure how it indicates a problem..... There's a hose that feeds the air pressure and oil vapour back into the inlet manifold (to burn off oil vapour), it could be blocked up with gunge..... Which would indicate it not been serviced correctly.

Gloomendoom

If he takes the oil cap off it can mean that the engine runs lean. Prolonged lean running can cause damage.

Essentially, it screws up the fuel/air mixture so it runs like a bag of nails.

If there had been no change in how the engine ran it would indicate that there was probably a blockage in the crankcase ventilation system.

Hammyman

No he hasn't done any damage. Gloomendoom is right in the description of what is occurring but for the time it was off, no damage will be caused.

davetrousers

dada44 wrote: »

He did this a couple of times and pointed out that something might be wrong with the engine?

He is trying to play on your naivety, so that he can haggle you down!

skiddlydiddly

I thought it was to check for excessive blowby in the cylinders ie gases escaping past the rings?

forgotmyname

Excess pressure would point to a worn engine, I always removed the cap with the engine running, It should not
make any difference to the way it runs. Maybe yours has excess pressure & being forced into the intake and is
fuelling to compensate for it?

It will not cause any damage, Unless they sat there revving the engine until all the oil was sprayed out of the hole.
How much oil does it use?

Lum

skiddlydiddly wrote: »

I thought it was to check for excessive blowby in the cylinders ie gases escaping past the rings?

This is why I do it.

Also, depending on the specific cars, there are other things to check, e.g. on the Nissan SR20 engine a common fault is that the cam spray bars clog up which means the cams are starved of oil and it eventually causes an expensive failure when the swarf from the knackered cam shafts travels into the rest of the engine. So you take the cap off and have a look if oil is being sprayed on the cams correctly.

optimus_primera

Lum wrote: »

This is why I do it.

Also, depending on the specific cars, there are other things to check, e.g. on the Nissan SR20 engine a common fault is that the cam spray bars clog up which means the cams are starved of oil and it eventually causes an expensive failure when the swarf from the knackered cam shafts travels into the rest of the engine. So you take the cap off and have a look if oil is being sprayed on the cams correctly.

HMMMMMM didn't know that one ............ i'll have to check on my one then ......