Hey guys and gals,
I want to change the coolant on my 1973 Custom Cruiser (stock 455ci) and whilst looking for some good classic coolant I noticed some of them specified it must only be used on a pressurised system. That reminded me that the cap on top of the reservoir (expansion tank?) has all but disintegrated and will need to be replaced, however looking around online I can't find any that look like my one (pic below).
I have only owned this car since late last august (and so far this summer has been pretty rotten too) so haven't done any driving in hot weather, meaning overheating hasn't been an issue. There appears to be an aftermarket water temp gauge fitted and it always sits in the middle when up to temperature so I haven't been overly concerned but I have a long run to some shows etc in July and really want to make sure she's good to go.

This whole process has also made my question some things that I thought I knew;

I'm sure I read somewhere that it is a pressurised system but now can't seem to verify that. Is it pressurised?
Its also an iron block with iron heads too right?
Where can I get a replacement tank cap from and what are the two hoses? One has a hose that goes into the bottom of the tank but the other just seems to be some kind of return hose maybe.

Any light that can be shed on these points would be greatly appreciated.
Also if anyone has any particular do's or don't about coolant for these cars that would also be handy to know.

Thanks
Toby

 

The radiator is pressurized.That is the over flow tank, it collects the coolant, if pressure gets to high, it goes in there instead of on the ground. Check the one hose must come from the radiator, by the cap. That tank is not pressurized,radiator is. Did you check any of the Olds aftermarket sites? Like Fusuck? Also you want to use the green coolant, 50-50 with water, also get a new radiator cap.

 

Do's and don'ts...

Do flush the system before filling with new coolant. I'd suggest CRC ThermoCure.

Do remove the block drain plugs to get a good thorough flush. There is one on each side of the block, 9/16" hex head near the motor mounts.

Don't exceed 50% coolant.

 

And, use distilled H2O.

 

Thanks for all your information and useful tips, I shall be looking around and perhaps even just make my own cap if it doesn't need to be hold pressure.
I'll let you guys know how it goes.

 

One of these caps might work for you:

 

Yeah they look correct, however they aren't available on the UK amazon.
I didn't realise they were the same as the C3 corvette, parts for them are quite readily available in England so I should be able to source one pretty easily.
Thanks for the inspiration.