Alright, so to start I've got low oil pressure. Checked with a mech. gauge and it idles around 50-60psi, then decreases under throttle down towards 20-30 as rpms increase. Tonight I went to drain the oil before pulling the oil pan to check the oil pickup/regulator/general health of things, and found this when looking in the filler neck:


That's my filler neck. Now, I'm not a doctor but that looks like foamy coolant. The flash on my phone makes it look very green, but really its a yellow/green color. There is no trace of it in the oil I drained out, or the oil I flushed with.

The motor is about 15k into a rebuild done by the previous owner. The car still idles very very rich as I chase down throttle body gremlins, so there's gas in the oil. It's also coldish out here in VT, and the car has had a few short low-rpm trips in ~40 degree weather. It doesn't seem to be consuming coolant, and the exhaust is actually colorless, no white or black smoke at all. Maybe its 'lung butter'?

Anyone have thoughts? All things being equal the car runs strong and seems perfectly happy. I don't want to go get this thing rebuilt but if I have to..

There are a stupid number of modifications, so here's a link instead of listing them:
build page
I'm going to pull the oil pan off and have a look.

 

Its a PITA to get my phone camera to focus down the neck but here's another:




I've always had a small amount of condensation in the neck when changing oil but this is extreme.. if its even condensation..

 

Also, no oil in coolant, changed that about a week ago.

 

have you checked your crankcase vent is not blocked and working properly? that could cause whats in the oil filler neck as the condensation isnt being drawn in by the engine.

 

due to the way the engine is built the coolant would have to leak from an outer coolant seal, which is really rare, and then it would have to leak back in to the oiling system, without of course being visible, or getting on the ground.

or conversely the rotary doesn't have a head gasket.

there is a way for coolant to get into the oil, but since a freeze plug has to fail, ALL of the coolant goes in the oil.

what you're looking at is condensed steam from the highest point in the oiling system... it means you either need to drive it more, change the oil more or look at the PCV system

 

Thank you. I needed to hear it from someone(s) else. The fact that its green/yellow was just really throwing me.. I checked the valve coming off the filler neck and it seems to be 1-way functional as it should, and the lines are clear so I'm not sure why it wouldn't work. Thinking I'll try the "drive it more" theory since this is the first time I've had it happen, once I fix the oil pan that is. Someone was a big fan of rtv and there is no way its coming off without getting destroyed..

 

scrape off the majority of RTV with a plastic scraper or use something a bit harder but be carefull not to wreck the flat surface.
then clean the rest off with acetone.

 

How long were you driving for before you noticed this? It's not terribly uncommon to have a little bit of froth in the filler neck if you're only making short trips. Go for a nice long drive (an hour or so) at operating temperature then check again.

 

1. Thanks for the RTV cleaning tips, its a pain.

2. The car had been driven on 3 successive ~10-20 minute trips between places (looking at cars for the lady). Then it sat for 2 days before I got into working on it. It reached operating temperature each time, but thinking about it this makes a lot of sense. After some more reading I see there's a second PCV line to before the primary turbo so I'll check that too.

 

Normal to have that in the filler neck. Dont worry about it.

 

Yea moisture in the air oil heat it's normal no worries

 

When normal driving in winter or cool weather, especially with dual oil coolers, the oil does not get fully warned up. Thus the oil/water moisture/blow by sludge forms.

I first noticed it back in 1968 while in Germany. My Alfa Romeo intake plenum would have it where the crank case breather hose was.

If you have dual oil coolers, block one off.

Upon getting back to your abode, partially pull out the oil dipstick and remove the oil cap.
This allows some of the bad vapors to escape.

 

 

Its EXTREMELY rare for an outer coolant oring to fail on these motors. From the pictures it looks like condensation from moisture in the oil. Running a catch can and allowing the car to always get up to operating temperature when you run it help. As far are your oil pressure, verify it with a quality aftermarket gauge from the stock sender location on the rear iron. The mazda fsm details the procedure. If you have low oil pressure Most likely culprits are the oil pump or the regulator. For the oil pump worn internals or a missing key would be things to check for. A massive oil leak would also cause it but would be pretty obvious.