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MG MGB Technical - White smoke
|I was on highway driving at 120 km/h (75 mile per hour) in top gear when suddenly I smell oil so I checked oil pressure gauge and noticed drop of pressure (45 psi). Then I look to mirror and behind me was white smoke like in James Bond action. I pull aside and come back home on back of trailer. |
In garage I restart engine and it idles nice white no smoke, pressure at 50 psi. But when I rev up to 4000 rpm smoke comes out again. Also back of car is pretty oily. I thought that is problem blown head gasket, so yesterday I took head off but gasket looks just OK. I noticed heavy deposits in cyl #2 and #3 so oil must come to those to cylinders – but good news is that there is no oil in cooling system.
So what else could be problem for oil in combustion chamber if not gasket? OK valve steam seals were all off so I don’t think that this would cause problem only in 2 cylinder in that case should oil penetrate in all 4 cyl (please let me know if anyone have source of good steam seals – I tried many sources but all slip off after while). And IMHO quantities of oil are too small for that kind of problem.
Next logical step would be piston rings – but on two cylinders at same time? And that shouldnt have any relation to oil pressure. Beside that engine made only 10k miles after build.
|Toni, White smoke means the engine is burning coolant or transmission / brake fluid. If the white smoke is coolant, the cause is likely to be a leaky head gasket or a crack in the cylinder head. If the white exhaust smoke is transmission / brake fluid, the engine is sucking fluid through a vacuum hose (have you checked the vacuum pipes, servo etc?) If you see continuous white smoke while driving it could also mean a loss of compression in one or more cylinders.|
|What year i.e. do you have the PCV valve on the inlet manifold to ventilate the crankcase?|
That sits between 2 and 3, so excessive oil via that could contaminate 2 and 3 more than 1 and 4, and give rise to excessive smoke from the exhaust. However that would normally be blue, white is normally as Andy says.
Check the valve and it's hose, and if oily the valve could have failed applying full manifold vacuum to the crankcase rather than a very low suction. Could also be a problem with rings and excessive crankcase pressure blowing oil via the PCV, really you should have done a compression test and a PCV oil trap test before removing the head.
|Toni, I had a similar problem with my XPAG engine, it turned out to be the head gasket. Let's hope that's all it is with your engine.|
|Thank you for input. We can eliminate PCV as source of smoke (oil) since I modified intake (see previous thread – Dyno) and engine use oil catch tank that isn’t connected to intake.|
Will clean head and look for cracks (that could be also one option) and tomorrow will get compression tester for few hours so I can measure compression and tell you more details.
|Coolant in the combustion does produce copious amounts of white smoke, but usually the smell gives this away. That sweet smell of anti-freeze is quite pungent.|
Also check your brake fluid level. If that has gone down significantly your servo could be drawing fluid into the vacuum side of the "can" through the rear seal. This does however usually empty you fluid reservoir very quickly!
|Meant to also say, take the plugs out. Coolant in a combustion process will give a very clean, "washed" plug!|
|Definitely check the brake master cylinder level. The remote servo can fail in such away that the brake fluid is sucked into the inlet. The first you know is that heart stopping moment when the pedal goes right to the floor. This has happened to MGB owners before, so check.|
|As Paul has said it would have been better to diagnose this fault first before you stripped it out, rather than a compression test, it would have been better to do a cylinder leak test, which would also have checked the head gasket and cracks in the combustion chambers, if you don't have access to a cylinder leak tester, you can make one with old spark plug and a hydrolastic suspension valve, a tyre inflator and an air supply,|
|This will be very embarrassing now. As I mentioned I have oil catch tank. Since I replaced old good SUs with EFI I discontent vacuum that goes from intake manifold to PCV, just to prevent oil to contaminate and kill O2 probe. To replace vacuum source from intake manifold I made one that use exhaust gases (http://www.kmnet.demon.co.uk/arnold/evac2.jpg). So I used check valve and some hose connected to oil catch tank. But it looks that exhaust gases create so much vacuum that was oil tank full after only 3 weeks so at the end oil overflow and find way to exhaust. Today I just drain oil, put head back on block (with new gasket) and run engine. When all cumulated oil burned out smoke simply disappeared. |
It looks that this create way too much vacuum.
|Sounds like you need a PCV valve in your exhaust vacuum line as well as the check (one way valve?) valve. Didn't you notice high oil consumption?|
However I wouldn't expect oil from the standard crankcase ventilation to kill an O2 probe unless you were burning excessive oil from a fault.
|I have only one way valve to prevent backpressure from exhaust. Maybe was too big, maybe I should use one with smaller diameter or put inline valve to restrict vacuum. In oil catch tank was 1,2 l of oil and that was missing in engine. As I wrote I noticed low reading of oil pressure.|
I learned that is PCV pretty complicated – if it works as it should. I used pretty big tank, it holds 1,5l then I weld in partition wall to separate inlet and outlet and then filled one chamber with stainless steel pads– those help condensate oil. Now I am looking to relocate mounting position (it is under front wing). I will mount it higher and add drain hose that will allow oil that condensate to go back to engine. And for vacuum source will go back to intake.
Maybe you are right regard O2 probe but on EFI forums you can read a lot of different stories. It looks that is best to try yourself :)
This thread was discussed between 12/09/2016 and 16/09/2016
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