Hot start smoking - Specific Circumstances

[StrongSpearWorks]

Hi,

My new to me 940 turbo (1991) has an issue where if I drive it for a while (up to temprature) then park up for say... 15 mins, when I start the car again, not imidiatly but after quater of a mile or so I get plumes of white/blue smoke coming out the exhaust and a rancid smell coming into the cabin.

I thought initially it might be crank case pressure forcing oil back into the turbo and it burning, but i've changed the PCV box and cleaned out the hoses, and the intercooler side is clean.

No determinable end float on the turbine...

Any thoughts on what to look at next?

[Laird Scooby]

Originally Posted by StrongSpearWorks

Hi,

My new to me 940 turbo (1991) has an issue where if I drive it for a while (up to temprature) then park up for say... 15 mins, when I start the car again, not imidiatly but after quater of a mile or so I get plumes of white/blue smoke coming out the exhaust and a rancid smell coming into the cabin.

I thought initially it might be crank case pressure forcing oil back into the turbo and it burning, but i've changed the PCV box and cleaned out the hoses, and the intercooler side is clean.

No determinable end float on the turbine...

Any thoughts on what to look at next?

When you park, do you let the engine idle for a couple of minutes before switching it off? It sounds very much like the oil is getting past the turbo bearings while it's still spinning and leaking into the exhaust. When you next start the engien, the turbo spools up and starts the oil burning. It's surprising how little end float makes a difference but it's more about the the radial play (out of round) in the shaft than the axial play (end float) that lets the oil through. Could also be worth cleaning the intercooler and the intake trunking between the turbo, intercooler and throttle body.

[StrongSpearWorks]

I usually let it idle for about 30 seconds - a practice from owning a succession of Saab 900 turbos*. I’ll let it idle for longer from now on and set about cleaning the parts you suggested.

Of interest, perhaps, is I have a rather wet oil return / drain. Potential for clogs there? I have a replacement gasket for the bock... it’s having enough time to get it in the air and replace it at the moment, but could a blockage here also foul the turbo maybe?



* 3 in total, all wanted to ruin me financially in one way or another. 😂

[Laird Scooby]

Originally Posted by StrongSpearWorks

I usually let it idle for about 30 seconds - a practice from owning a succession of Saab 900 turbos*. I’ll let it idle for longer from now on and set about cleaning the parts you suggested.

Of interest, perhaps, is I have a rather wet oil return / drain. Potential for clogs there? I have a replacement gasket for the bock... it’s having enough time to get it in the air and replace it at the moment, but could a blockage here also foul the turbo maybe?



* 3 in total, all wanted to ruin me financially in one way or another. 😂

There could be blockages, i'm not as familiar with the turbo set up as others but i believe there is an "O" ring (square section? Maybe the gasket you refer to?) between the oil drain tube from the turbo and the block where it returns to the sump. Also worth noting that the coolant hoses feeding the turbo can block up causing the turbo to get hotter than it should - this could thin the oil so it gets past the seals easier.

I've only ever had one Saab, a 1986 900i Combi - that also wanted to ruin me financially and that was just on the fuel consumption! Maximum of 22mpg on a very good day, normally about 15-18mpg! Considering i'd downsized from a Nissan 300C (3.0 V6 auto) that gave 30-35mpg regardless, i was horrified at the Saab!

[StrongSpearWorks]

Originally Posted by Laird Scooby

Also worth noting that the coolant hoses feeding the turbo can block up causing the turbo to get hotter than it should - this could thin the oil so it gets past the seals easier.

Interesting... I think the previous owner chucked some k-seal in to try and hide the weeping heater core (another fun job down the line) so perhaps those smaller hoses are being restricted by that gunk.

Full flush coming soon I think.

[john.wigley]

Originally Posted by Laird Scooby

There could be blockages, i'm not as familiar with the turbo set up as others but i believe there is an "O" ring (square section? Maybe the gasket you refer to?) between the oil drain tube from the turbo and the block where it returns to the sump. Also worth noting that the coolant hoses feeding the turbo can block up causing the turbo to get hotter than it should - this could thin the oil so it gets past the seals easier.

I've only ever had one Saab, a 1986 900i Combi - that also wanted to ruin me financially and that was just on the fuel consumption! Maximum of 22mpg on a very good day, normally about 15-18mpg! Considering i'd downsized from a Nissan 300C (3.0 V6 auto) that gave 30-35mpg regardless, i was horrified at the Saab!

That does seem rather excessive, 'L.S', are you sure that there wasn't a hole in the tank?

All of our Saabs have returned comparable figures to our Volvos when used under like-for-like conditions. My current 9-3 2.0 LPT 'vert has returned almost 29 MPG over 8K miles and Linda's 3.0 N/A 9000 25 MPG over 22K. My 2.0 LPT 9-5 'wagon returned almost 34 over 37K, but that was mainly used for work doing high daily mileages with only a couple of cold starts. All of the cars were/are petrol automatics. Your 900 would have been quite an early injection, but that should have helped economy, not hurt it.

Regards, John.

[StrongSpearWorks]

Don’t know about that. All three of mine were “classics” and never managed more than 25mpg.
HPT or LPT, all manuals (first one was a flat nosed 8 valve which sometimes started but mainly didn’t).

[Laird Scooby]

Originally Posted by john.wigley

That does seem rather excessive, 'L.S', are you sure that there wasn't a hole in the tank?

All of our Saabs have returned comparable figures to our Volvos when used under like-for-like conditions. My current 9-3 2.0 LPT 'vert has returned almost 29 MPG over 8K miles and Linda's 3.0 N/A 9000 25 MPG over 22K. My 2.0 LPT 9-5 'wagon returned almost 34 over 37K, but that was mainly used for work doing high daily mileages with only a couple of cold starts. All of the cars were/are petrol automatics. Your 900 would have been quite an early injection, but that should have helped economy, not hurt it.

Regards, John.

There was a hole in the tank John and it fed straight into the engine!

I did all the usual checks to ensure it would return good economy but i think being a K-Jet auto probably didn't help.

[360beast]

Love saabs, proper ones not the glorified Vauxhalls. My dad has a 9000 2.0 LPT with a stage 1 Jules Holland tune so now has 220hp.

[360beast]

Every time I take an intercooler off a 940 there is loads of oil inside of it, chances are yours needs the intercooler cleaning out for a start and see if that improves matters. If there is oil in the intercooler (I bet there is) then oil is getting past the turbo seals.