Cooling System Cleaner - Oil Residue

[Beatle]

Hi again.  I'm chasing suggestions for a decent cleaner to run through the 2.5V6 in my 90 to clean out oil residue.   The header tank has a light film in it (the car sits for months) but I'm not sure if it's a newly failed headgasket, or residue from a previously repaired gasket.  The PO indicated that he'd done a headgasket along with WP, timing belt etc.  

I'd like to clean her out to confirm either way (no evidence of any coolant in the sump).

If the gasket is leaking/seeping oil into the coolant, is there any hope apart from pulling the heads?  The car only has just over 116,000kms and is rarely driven, so if I retorque the heads and use the car more often what are the chances things will seal up?  

[colcol]

How much would it cost to run a cleaner through the cooling system?, $10, just do it, brand to use, no idea, but i use NULON, and some recommend to remove thermostat, for a bit more flow, with less restriction, depends on how difficult a 90 stat is to remove, if possible, do a compression test, and then remove valve covers, and slightly loosen head fasteners, and retorque them in correct sequence, you should retorque the heads every few years anyway as the fasteners stretch and the alloy blocks move around, and then if possible do another compression test and see if it made any difference, Colin.

[Beatle]

Thanks Col, I just wasn't sure if the normal cleaners worked on oil.  I thought they were aimed at corrosion and hard deposit removal.

I'd also expect a leaky gasket to be pretty bad for a head retorque to make a discenable firrence in compression, and the engine runs fine so I don't suspect there is a compression-to-coolant leak at all.

[colcol]

The cooling system cleaners have a certain amount of detergent in them to clean the system, leave them in as long as you can, i don't think that 15 minutes is enough, i have left them in for up to a month, without any damage, if there is a leaky head gasket, it will show up with slightly lower compression, in the leaky cylinders, Colin.