Pressure in cooling system.............
 

Took a rock to a fog light the other day.got around to pulling it today and noticed that the top hose of radiator was under pressure?Car has been in garage for couple of days,so definitely not warm.Can anyone tell me what might cause this or if it is normal.thanks....

Exhaust gases in the coolant system, typically caused by a bad headgasket or cracked head. Not a good thing. Can't think why else there would be pressure after that length of time. There is a kit which tests for presence of exhaust products in the coolant.

Is it reasonable to assume that due to a definite lack of white smoke,no oil in coolant or vice versa(coolant in oil) , only seems to need a small bit of coolant after long highway drives, and does not overheat and has not overheated at all in the time that I have owned her; That I may have caught it before it has really blown?
Is it possible that my thermostat has gone bad and is not allowing coolant to properly pass it?Car runs happily at 75+mph,and does not overheat.On long uphills it sometimes gets a bit warmer but never above the 100 mark on gauge,and only when going fast.IE-really pushing it up the hill.
If I do have to fix my HG, I understand that there are a few special wrenches and/or bolts needed.Could someone Identify these by name or part number please.

Given the lack of other symptoms, I'd replace the radiator cap, test the coolant for presence of exhaust products and see what happens.

A small head gasket leak won't produce many of the symptoms that you describe.

You don't currently know if there is coolant in the oil............unless you've had a oil analysis performed. This would be the definitive test for presence of glycol or not.

Unless you have a leak in the cooling system, it's likely that your loss of coolant is via the head gasket.

I say its normal. The cooling system will hold some pressure for a long time. Even after 2 days of not running, my upper hose will still have some pressure.

It is not normal on vehicles with an expansion tank. A properly operating system will have a slight vacuum when the cap of the expansion tank is removed. If you're running a 240D without any expansion tank, your scenario can be considered normal.

so far,I have found.....
 

This afternoon I took the coolant system partially apart.Why you might ask...
After running car to temp(my gauge reads about 85-90C) and removing expansion tank cap I did not see any bubbles occurring at idle or while revving.Also, still no white smoke(and not much black either for that matter).heat in car works VERY well now and comes right up to temp at full blast.no smell of coolant either.back under hood,notice that top of rad is hot and bottom is not?squeeze upper and it sounds like splashing in an empty room,hollow!expansion tank is full.....top of thermostat is hot,but water pump isn't so hot(not cold).drain radiator and get about a pint more than a gallon and no more until I open thermostat.thermostat looks healthy(2 years old).tests ok.Starts to open at 80C and only gets wider as it gets hotter.working.water pump seems to work.How you might ask did i check.after removing radiator, fan and pulley,then the bypass(metal)line I hand spun water pump and water shot out the lower hole.I am not sure,but I think that is good.Also bypass line was not clogged.gonna flush rad and rest of system tomorrow and hope that I had a fluke problem and did not properly "burp" car after I changed thermostat.I know I am reaching,but I really HOPE it isnt a headgasket.anybody gotta motor they wanna sell......

any good suggestions on a location for a decent procedural for doing a headgasket for a 617.Done a few american cars and a bike or two,so I figure there must be a particular process for these as well.fsm wasnt much help for this sort of thing as i remember(cant find at present).

You need the FSM for that task.

May have to buy another.Too many moves this past 16 months.and now the baby is almost crawling;more things will "go into hiding"......
arent they only 20 bucks now on cd from the dealer?

*update*
 

upon deeper exploration of this new problem,I noticed two things-
1-water inrad at top with hose came out pretty slow at bottom.....partial clog?
2-after flush,refill,burp and test drive coolant is now weeping from top of radiator.
I am hoping that a partially clogged rad will be the source of my slight back pressure in rad hose.I think(correct me if wrong please) with the expansion tank cap working right,there should be something less than 16psi in coolant system even after cooling down(though obviously much less when cool or cold).After replacing cap I have little to no pressure now.
Back to number two.....
Is there an aftermarket radiator available that is all metal?not the metal/plastic combos.I thought I remember someone(roy maybe) mentioning this little tidbit in another thread(though I have been unable to find it).

Tom Walgamuth had an all brass(?) for sale on the forum not too long ago- maybe he still has it?