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Mon Aug 25, 2025 7:16 am

I think I have an unusual problem with white smoke on start up :D

With some hot starts I get white smoke from the exhaust.

What could be the cause?
Could I be accidentally pressing the accelerator before starting the engine? Unburned fuel ?
I have a 1385 with dual 34 carbs.

Thank you

Mon Aug 25, 2025 8:47 am

My dual carbed 1679 puffs white vapor out of the exhaust on hot start ups.
I believe it's excess unburnt fuel from heat soak while the car is sitting.

It doesn't do that during cold start us'

Mon Aug 25, 2025 9:00 am

White should be moisture, which shows up with cooler weather.

White with slight bluish tinge is oil being burnt.

Black is too much fuel.

Mon Aug 25, 2025 9:23 am

Now it's summer in Italy so I think that it can't be moisture :D

Mon Aug 25, 2025 10:35 am

62ItalianRagtop wrote: Now it's summer in Italy so I think that it can't be moisture :D

Then look for the bluish tint to the white. Assuming you are not high up in the Alps.

Mon Aug 25, 2025 4:39 pm

62ItalianRagtop wrote: Now it's summer in Italy so I think that it can't be moisture :D

But there is still water vapour in the air plus water is produced from the combustion process.

Just because it is dry doesn't mean there is no water in the air.

For example at 50% Relative Humidity and 35 degrees C, there is still about 20g of water in 1000 litres of air. This is called the Absolute Humidity and measures the actual amount of water in the air.

Have a play with some numbers on this on line calculator and you can see how it changes. Remember that if it is a hot day there will be more water vapour in the air. When the temperature drops that water vapour can condense and end up in your cylinder.

https://www.omnicalculator.com/physics/absolute-humidity

Tue Aug 26, 2025 12:16 am

Thank you guys but last summer I didn't have this problem :?

However, it doesn't always do this... with other starts with a warm engine, no white smoke.

I'll try to be more careful and check the smoke and oil level more closely.

Thanks a lot for now.

Tue Aug 26, 2025 8:34 am

Next time you pull the spark plugs, check if those are getting oil coating on them.

Tue Aug 26, 2025 11:43 pm

Ok, I let you know ! Thank you

Wed Aug 27, 2025 3:26 am

Worn valve guides, when it’s hot the oil is thin enough to get past guides and lay in the combustion chamber. Quick puff on start up and it’s burned off. Get someone to start your car during the conditions where it does it and put your hand in front of the exhaust and smell your hand for oil.

Wed Aug 27, 2025 3:36 am

pondoras box wrote: Worn valve guides, when it’s hot the oil is thin enough to get past guides and lay in the combustion chamber. Quick puff on start up and it’s burned off. Get someone to start your car during the conditions where it does it and put your hand in front of the exhaust and smell your hand for oil.

Ok, but I think that if this is the problem, I should have white smoke every time I start the engine when hot and also while it is running. Am I wrong?

Wed Aug 27, 2025 6:08 am

62ItalianRagtop wrote: I think I have an unusual problem with white smoke on start up :D

perhaps the vatican was a previous owner..? :wink:

Wed Aug 27, 2025 6:12 am

finster wrote: 62ItalianRagtop wrote: I think I have an unusual problem with white smoke on start up :D

perhaps the vatican was a previous owner..? :wink:

LOL

Thu Aug 28, 2025 5:02 am

Not when they are just starting to get out of spec. And once the the car starts the amount of oil getting through is minimal and you won’t see it. The oil will leak past because it’s warmer and will flow easier into the gap between valves and seals. As it wears it will do this on cold starts also.

Not saying that this is your problem just a possible cause. If it gets worse then most likely you’re cause. But please keep us posted.

Thu Aug 28, 2025 9:52 am

Blue smoke from an old VW is not unexpected.
Usually it's from the passenger compartment, though.

Thu Aug 28, 2025 10:17 am

Do keep in mind that due these old ACVW engines being that the pistons and cylinders are horizontal. Due to this oil can collect in the cylinder on the crankshaft side of the piston and seep thru the piston rings when the engine is shut off. Especially if one parks the VW where it is angled over to one side or another.