Rad flush?

[Avocet]

It's getting to that time when I ought to replace my coolant. (It's a 1980s car so IAT antifreeze (the blue stuff) rather than the pink stuff. Thermostat's been getting lazy anyway, so I have a new one of those to fit too. I haven't had any problems with the cooling system, but when I first bought the car, it had a leaking head gasket (which I sorted). However, there has always been a bit of oily residue on the inside of the expansion tank from that time.

Can any of you recommend a type of flushing agent to use before I change the coolant? (Or recommend any that I should avoid)!

 

[Burnerman]

I've used a Comma flush and was quite surprised at the grot that came out!
I'm also surprised at how much liquid resides in the block, and only escapes when the water pump is removed. You aren't due a timing belt / water pump change are you?
John

 

[Avocet]

Thanks John, that'll do for me! It's an older design (single V belt driving the water pump) and nothing to do with the cam belt (although the cam belt has to come off in order to change the water pump, just because it's "in the way"). The pumps are "old skool" with steel pulleys and impellers. Seem to last at least 100,000 miles. Even when they do finally fail, they make a grumbling noise from the bearings and then start slowly dripping water from the seal. You get several thousand miles of warning! Ahh the good old days....

 

[DaveHerns]

You might have a drain tap in the block. Why not remove the expansion tank and give it a wash? I think soap powder is recommended for that.