Any acceptable engine residue

[ngk]

My old car (91 polo) died of HG failure. As i'm not mechanically minded, only knew the signs to look for (creamy residue) after it happened. Now looking for another 2nd-hand car. Have seen two so far and both had varying amounts of pale brown creamy residue (mayo) on the engine cap. The first had it after a test drive (wasn't actually looking before the drive), the 2nd had a noticable amount before test drive. They were 1.4 '98 polo and 1.0 '99 lupo, respectively. Is there ANY acceptable amount of residue for used cars that may not have been driven for a few weeks/months? I read somewhere on a web forum that engine additives can produce similar residue as a by-product. Naturaly I don't want to buy a car that will become a problem prematurely, but also don't want to pass up good cars unnecessarily (both I would have considered buying if not for the gunk). For an engine novice is there any decent methods to assess if residue is due to anything other than problem water in engine? If just short-term condensation, how can i tell? Sometimes a good long test-drive is not possible or no close raods to pick up speed. sorry for so many Q's - i just don't have a big �� budget to make mistakes.

[Teddio]

Oil/water emulsion may appear on the oil filler cap if the car's been used for very short journeys and the engine hasn't reached its normal operating temperature. If the thermostat is jammed open the engine will run cold and this can also lead to residues.
Remove the dip stick. Does the oil look clear?
Look at the coolant. Does it look uncontaminated?
Has the car got a Rover K-series engine?

[Toureman]

99% of the time a Mayanaisse type residue under the oil cap just means the engine is running to cool even after a long journey nothing to do with a head gasket problem.

The only way I could cure this on an Astra i had was to block off part of the radiater.

Even if you went on a long test drive if it's there that would not get rid of it.

[weggiewabbit]

I am not in the trade, merely speaking from personal experience as I tend to run old, very cheap cars.

All my cars produce �mayonnaising� because I do very short runs most of the time. It doesn�t necessarily indicate any engine problem at all.

As Teddio said, when buying a car I always check the dipstick and the coolant for any sign of contamination of the oil or coolant. You don�t want to see any rust-coloured deposits in the coolant reservoir, or rusty streaks running down the engine block (these can be difficult to spot on some cars), which both suggest a dodgy head gasket. A low coolant level can also be indicative.

I did buy a cheap Polo not long ago which turned out to be a dog in several ways. I didn�t detect anything wrong with it when I bought it, and it ran OK for a few months, but I wouldn�t buy another one of those!

Some engines are more prone to this than others, but I don�t know which they are.

I�ve found Fiestas to be very good usually. Got an Escort now, which has been great.

[david1702198]

some of the older vauxhall engines were prone to this