Rust color in oil fill cap

[Tobygot]

Hi, I was looking at a used truck today w/ almost 100,000 miles on it and when I looked at the inside of the oil fill cap there was a rust colored layer in it.
Searching through this forum it looks like people are saying this is a varnish?
The truck has fresh oil in it so there was nothing to see there.

Is this a sign of neglect?
Would an oil flush or two be a good idea with an engine like this or should I look for another truck.

Thanks

 

[HTSS_TR]

Oil fill cap has the coolest temp therefore sludge/vanish can accumulate there, it isn't the sign of neglect but it's a good idea to do a short OCI of 1-2k.

 

[Scienceman]

+1

 

[hisilver]

Ive owned my truck since new and use good syn oils with reasonable OCIs and have a good layer of rust colored [censored] inside the plastic oil fill neck. I can use my finger and scrape it out. Truck has <50k miles on it.

 

[demarpaint]

It must be an indication of short trip use. My Aerostar has just about 190K on it and the oil fill neck all the way down to the valve cover is clean and free of deposits of any kind. The inside of the cap is clean as well. Mine sees mixed severe service use.

 

[Craig in Canada]

One big difference to watch out for - some people's filler caps see full oil flow and some are protected by baffles so they only see oil "vapour" and water condensation.

If baffled, you're pretty much always going to see crud build up no matter how the vehicle is maintained. If full oil flow, then it should be relatively clean if well maintained.

 

[Sylvatica]

Oil mist deposition mixes with water vapor to form an emulsion there. If it is a soft deposit, it is not "varnish", which is caused by polymerization on high-temperature metal surfaces.

If a standard engine inspection checks as OK, run some ester-rich oil with a high detergent add-pack. Drive, drain, repeat, drive...