New radiator leaking at expansion tank

[jbourque]

I've been fighting with a leak at the bottom of the expansion tank on a new nissens radiator so I replace the tank with a new unit and added rtv sealant to ensure the seal, but I'm still have a leak coming fom there.

Anyone ever have this issue?

Tonight I plan of pulling it off again and putting more rtv but I know that can't be the proper solution? Any input would be appreciated and I'll update the group on the results tomorrow.

[jbourque]

Little update: tried a larger OD oring, but it would just roll out and the tank wouldn't seat in place. I bought a tube of silicone that is coolant resistant so I will proceed as planned.

[jbourque]

Silicone held up at the bottom, but when it warmed up it started to leak at the top seal. I pulled out the xpansion tanks and applied a little bead around the top seal and another bead in the valley where the original leak was. I'll give another try this afternoon.

Side note- blue silicone is holding up nicely, much better than the orange copper rtv

[roguetoaster]

Somehow I believe you have a radiator that has a flaw as the coolant expansion tank should be a very tight fit with the correct gaskets, and should not require any additional sealant to work properly.

It also surprises me that you'd attempt to repair a new part out of your own pocket rather than sending it back for replacement.

In any case, I'd suggest that you really inspect both parts for defects or damage before attempting to install it again with fresh o-rings and a bit of lubrication for the install.

[jbourque]

Somehow I believe you have a radiator that has a flaw as the coolant expansion tank should be a very tight fit with the correct gaskets, and should not require any additional sealant to work properly.

It also surprises me that you'd attempt to repair a new part out of your own pocket rather than sending it back for replacement.

In any case, I'd suggest that you really inspect both parts for defects or damage before attempting to install it again with fresh o-rings and a bit of lubrication for the install.

I would normally send it back for a new part but the radiat or is out of warranty so I was just trying to get it fixed.

BTW- the latest attempt has failed. The old unit will be going back in.

[TobyB]

I have only had luck with Behr
rads on the M42. Nissens works on the M20,
but like you, I had sealing issues with the M42 expansion tank.
E36, in my case...

t

[AndrewBird]

You might have a leaking head gasket that is over pressurizing the cooling system. Buy a hydrocarbon tester and test your coolant.

[TobyB]

... or a rad cap that's not releasing at the right pressure.

I wonder if the aftermarket rads are rated to the 'uprated' 2 bar BMW pressure...

t