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Author: Subject: breathers and smoke
luke2152

posted on 12/5/19 at 05:46 PM Reply With Quote
breathers and smoke

Something unusual happening with the 3sgte engine in my MR2 (admittedly not a kit car this time

Before I begin I brought it as a non runner, replaced all inlet pipework and megasquirt 2 so this is essentially the first time I've run it.

Rocker cover breather is vented to atmosphere for now at least. Once fully warmed up it smokes like a bastard at idle, thick blue oily smoke which I'm presuming to be coming off the valve stems. If I cover the breather it instantly stops smoking. My brain tells me that blocking the breather should make it worse not better. When I block it a small vacuum can be felt which again boggles me because surely the blowby should be creating slight pressure and not vacuum.

Under load the engine makes no visible smoke whether breather is covered or not.

Should I be running the hose to the inlet side of turbo or even to the outlet side but with a 1 way valve to stop from blowing boost into the engine.

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Mr Whippy

posted on 13/5/19 at 06:33 AM Reply With Quote
Stick a one way valve in it so it only vents with positive crank pressure and then connect it to the inlet. Given your description this will sort the smoke.
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nick205

posted on 13/5/19 at 09:15 AM Reply With Quote
Blue smoke to me indicates oil burning and usually either valve stem seals or potentially piston rings and oil coming up that way and burning.

I'd also expect the smoke to be coming out under a slight outward pressure and not a vacuum.

Is there anything else non-standard about the setup?

Perhaps some sort of circulation process whereby the blue smoke would normally be taken back into the engine and burnt off?

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MikeRJ

posted on 13/5/19 at 10:59 AM Reply With Quote
When you say it smokes, presumably you mean from the exhaust?

The behaviour you describe is mostly expected; there will be a PCV valve in the system that draws a vacuum in the crankcase whilst there is manifold vacuum present. Obviously this vacuum can only exist with the oil filler cap in place, and helps prevent oil getting past both the piston rings and the valve seals. However you still shouldn't be getting any significant blue smoke with the oil cap removed, so this does suggest something is worn.

My suspicion would be the turbocharger. Crankcase vacuum helps to ensure that oil in the turbo bearings gets drawn back through the oil drain rather than through the exhaust side seal, particularly when the turbo is worn. On my MR2 the turbo was pretty worn by 100,000km, and the smoke became really evident after I removed the remains of the cat internals that had broken up and partially blocked the exhaust (exhaust back pressure also helps prevent the seals leaking in worn out turbos ).

If it's knackered it would be a good excuse for a turbo upgrade, especially if you have the asthmatic old CT26A (Rev1/Rev2 cars).

[Edited on 13/5/19 by MikeRJ]

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coyoteboy

posted on 13/5/19 at 08:09 PM Reply With Quote
Turbo oil seals. Had exactly the same problem myself on the same engine. Venting the positive crankcase ventilation to atmosphere is a mistake, and it was only shortly after doing so that my turbo seals failed and took out the turbo.





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killerferret666

posted on 15/5/19 at 07:50 AM Reply With Quote
Which Rev is the Mr2? I have one in my kitcar. Ive done alot of engine work due to my first engine being a bit of a dud.

If its a rev 1 -2. It wont run without the oil cap on anyway so cant be checked that way, it should stall (or due to air leaks...just about run ) due to the older type sensors used. Rev3 onwards would be ok.

As for the breather, the original setup is to the inlet side of the turbo. No one way valves or anything like that.
I actually have mine like your current setup and venting to atmosphere but without the smoke. I'm not sure I would just plum it in and forget about the smoke though at this stage.

Turbo seals - will be some blue smoke when you floor it, normally a puff and gets worse over time. Not normally on idle.

So my educated guess would be piston rings or valve seals.


What oil are you using?
Ensure no pipes are kinked / caught as well

Cheapest first test to do is cylinder pressure test. Can buy the tool off ebay, it just goes in the spark plug hole.

* First run the car to warm
* For the test and turning over ensure your accelerator is pushed to the floor.
disconnect fuse for EFI, take all spark plugs out (just makes turning over easy), put tester in spark plug hole and work your way along the cylinders turning it over. Noting down the readings.


These things are always harder when a car has been sat still for a while as rubber bits dry out and becomes a hunting game!





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