Mayonnaise

[Spoonbill]

Hi all my wife's Chummy has emulsion on the oil filler cap but the oil is still clean? I am using a good quality 20/50 (Valvoline) that I use in my other vintage cars. It may have been doing this before but not aware of it. Long runs doesn't seem to boil it off. Any ideas please? Many thanks

[Zetomagneto]

It’s not running hot enough, fit a thermostat in the top hose

[Chris KC]

Have you tried cracking open the sump plug to see what trickles out?

For what it's worth, oil temp and water temp are only cousins - not as close a relationship as is oft assumed.

[mk1-mark]

This is a very common issue with cars that are not used regularly, a little more heat when the engine is running should boil this condensation off fairly quickly. Emulsion or mayonnaise is only an issue if the oil in the sump is looking that way.

[Ruairidh Dunford]

Try blocking off about a third of the rad with cardboard, temporarily, this should allow the engine to get up to proper temperature and it will most likely disappear.

[Hedd_Jones]

My chummy does this, and it runs hotter than the saloon. But it doesnt get many very long runs

It also has an aftermarket valve chest cover with no breather holes.

I stopped worrying about it when I changed the oil and found no water in it.

[Bob Culver]

I ran a Javelin car for decades. These are notorious for water in the oil by a myriad pathways. Mayonaise in the filler was the first sign. Oil would turn khaki but a long run would boil the water out of the oil to the extent that the dipstick fell markedly and drained oil appeared perfectly normal. No apparent harm but no roller bearings.

At least the original crankcase ventilation should be maintained (With none at all oil tends to work past the return scrolls. )
My Seven had experienced a period of severe main bearing wear corres a lot of short running. I ran it with a vent at the filler and a pipe from the valve chest into the aircleaner . No further trouble but the running was much altered.
The scope for water leaks with a Seven is limited but the oil level should not rise much after long standing.