Hi,
I could clearly see a steady stream of air bubbles in the coolant expansion tank. Does it necessarily mean that I am doomed by a leaky head gasket? Or maybe there is hope and I have a easier problem to fix ? My car seems to be O.K. - starts normally, coolant temperature stays within 80-90 degrees C, etc., etc.
Thank you.

First, I don't want to scare you. It might be something simple.

That said, I think you'll be lucky to be doomed by a leaky head gasket.

Do a search on 'head cracks' for some ideas as to what might be going on. Many of the threads include diagnostics.

Sixto
91 300SE
87 300SDL
83 300SD

Sixto,
Thank you for your reply. If you are pointing at the well documented head weakness of the 87 300D I hope it's not a problem in my case. At least it has not been up to this point. Simple "head tests" has been positive so far (i.e., no cracked head).

Have you done a pressure test on the cooling system?

__________________
2004 VW Jetta TDI (manual)

Past MB's: '96 E300D, '83 240D, '82 300D, '87 300D, '87 420SEL

DieselAddict,
If I understand you correctly, you mean to check whether the coolant pressure is withinh MB specs. No, I have not done that. I have performed what Dave (gsxr on this board) refers to as a "head test: " The 1987 300D/TD has an issue with the head cracking, due to a design flaw in the original heads. Later heads were beefed up. The early symptom of the crack is high pressure in the cooling system when cold. Normally, with a cold system, there is almost zero pressure, or possibly a slight vacuum (upper radiator hose kinda flattened). With the cracked head, the system
remains under abnormal high pressure when cold."
Hope Dave would not sue me for quoting him without proper authorization. Anyway, according to my last "head test", my car's head was not cracked.
Thank you.

I think DieselAddict means applying pressure directly to the cooling system. You can buy (maybe rent) a pump that fits in place of the reservoir cap. See if the system will hold to spec. See if air or coolant leaks out through the cylinders, manifolds, etc.

Sixto
91 300SE
87 300SDL
83 300SD

Sixto got it right. I have no idea how much it costs to buy or rent the pressure testing machine, but a decent shop will do it for you for a small fee. If you have a cracked head or leaking head gasket, this test will let you know.

__________________
2004 VW Jetta TDI (manual)

Past MB's: '96 E300D, '83 240D, '82 300D, '87 300D, '87 420SEL

Hi,
This coming Monday is gonna be the size of Texas for me. Will change the turbo, charge the AC, and try to not faint over the results of the head/gasket test. Still, besides those major enjine blockbusters , are there any minor things that could cause a stream of air bubbles in the expansion tank? It will help stay alive until Monday.
Thank you.

Provided that you are not loosing coolant or have not recently changed it or drained it for some other reason, the gas bubbles have to be either combustion gasses or steam. Since it isn't overheated, i'd guess leaking head gasket or cracked head ULESS you are looking in there with the engine at operating temp, in which case it could just be boiling coolant, especially if you shut a hot engine off and look in at once.

If it's bubbling cold, you have a bad head gasket or cracked head.

Check for oil in the coolant tank -- usually shows up before coolant loss, but not always.

Check for coolant in the oil, too -- if there is ANY evidence of coolant in there, fix it at once, the bearings will be ruined in short order!

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!