Large amounts of white/grey smoke on my 1974 Datsun 260z

[jjslade]

Hi there,



i've got a 260z with roundtop SU carbs on, 137,000 miles, it idles like a bag of spanners, and emits a ridiculous amount of white smoke out the back. Normally you would think this would be a blown headgasket, but it is a brand new headgasket, torqued down correctly. I have even tried draining all the water from the system and starting it for a short period with no coolant, but with the same cloud of white smoke. What else could this be? a warped head maybe, or vacuum leak? Really getting to my wits end with it now

Here is the compression test:

1- 100

2- 95

3- 90

4- 95

5-90

6-90

So very low. Could this indicate that my piston rings have gone? I also had to replace all the valves in the engine and reground them in myself. Perhaps I have not done enough of a good job, but do not see how this could cause all the white/grey smoke. I can post a video if need be

Cheers

[gtviva]

Isnt white/grey smoke brake fluid? if so could be the master cylinder has failed leaking into the servo and sucking the fluid in through the vacuum pipe on the inlet manifold

[jjslade]

Aug 19, 2020 11:12:11 GMT gtviva said:

Isnt white/grey smoke brake fluid? if so could be the master cylinder has failed leaking into the servo and sucking the fluid in through the vacuum pipe on the inlet manifold

I'm restoring the car at the moment and there isn't currently a master cylinder in the car

[Ritchie]

How does it smell? If it's oil it will stink but it wouldn't really be white.
Is there any chance there is water in the exhaust boiling off?
How long have you run it for? Even though you have run it without water in it, there might be residual water in the cylinders.
You really need to fill it with water and give it a good run up to temperature to ensure everything is burned off.

The next thing I'd do is a coolant pressure test.

[rapidyellow]

white smoke is usually just steam, I would make sure the cooling system is all connected and filled, and run the engine at say, 2000rpm for 10 mins or more and see if the smoke clears once the steam has evaporated and the engine and exhaust are fully hot.

[landruster]

I had massive overfuelling on an old scimitar and it gave off white smoke. That was overfuelling so badly it barely ran.

The fuel pressure was too high and the float chamber overflowed straight into the inlet manifold.

Strangely enough it stank of fuel so not much guesswork.

[Phil H]

White smoke can be oil - been there, had that smoke screen.

Compressions that low are worrying - you can try a “wet” test (squirt some oil down the plug hole and try again) but I’d guess it’s either knackered bores/rings or very knackered valve guides.