9 replies to this topic

[mbican]

Hey everyone a couple questions about an engine oil catch can. I have a new to me previously raced 1990 Spec Miata, second summer doing track days, hoping to race in the future. When I got it they had the breather tube from cam cover disconnected from intake going into an empty oil quart bottle. I hooked it back up and made a restrictor in tube as I have heard they had from factory and replaced PCV. I am getting blow by through breather tube after a couple hours on track it will be enough getting into intake it will start smoking, remove intake and full of oil. I am guessing that running high rpm with low vacuum is not allowing PCV to function.

So I am thinking installing catch can. Question is should i put it in the PCV hose and delete the PCV? Catch can without breather? Has anyone have this problem and what have you done, Thanks.

[Bench Racer]

My first question would be, why is the blow by so great? As to show oil in intake. 

Do a leak down test to see the percent leak down and listen for leak to possible item/items causing leak down.

 

If you have high leakage, you should listen for air hiss in the following areas:

Exhaust pipe – May indicate a burnt or stuck exhaust valve
Carburetor – Could indicate a bent or stuck intake valve
Oil filler or dip stick – Possible broken ring or piston
Radiator cap - Bubbles in the radiator indicates a leaking head gasket or cracked head

[mbican]

Did a compression test, 175 all four, plan on doing a leak down test. Does not start smoking until ran hard for five sessions, lap times four seconds above track records at Pitt Race and Nelson Ledges, car seems to run well. Nothing is going through PCV, no oil in that tube at all.

[Bench Racer]

There's oil getting into the intake via the breather tube. Is the oil at the dip stick full mark or has it been above full? Above full during the previous owner's time or your time could cause the issue. One step at a time, do the leak down and provide the info.

[Ron Alan]

Crankcase pressure...rings would be my guess?

[mbican]

Did a leak down test, #1 25%  #3 10%  #4 10%  #2 20%. Put some oil in #1 % went down to 5 %. Guessing it is tired rings.

[luvin_the_rings]

Did you listen to where the air was escaping from? dipstick, intake, exhaust, coolant?

 

You could save yourself a head rebuild if the valves are OK. 

[mbican]

It was leaking pretty good through the breather tube, plugged everything up built lots of pressure, valves seemed ok.

[davew]

My suggestion would be to put the PCV and breather system back to 100% stock configuration. Use a new PCV valve. Put fresh oil in, probably something in the 20w-50 range so you know you are plenty thick. Do NOT overfill. And monitor your oil level and intake condition at the next event.

[mbican]

Tried a new PCV valve and stock piping at last track day, didn't start smoking until after fifth session. Got new valve from auto parts store, heard somewhere they were questionable, probably should get one from Mazda. Have a three day event at Mid Ohio Labor Day weekend already paid for, too late for major repair.

Have been using Brad Penn blend 10-30, maybe try full dino oil 20-50.