Plumbing help please

dave wj · Post by **dave wj** » Mon Jun 18, 2007 1:36 pm

Hi guys,

A bit of a dumb question;

I'm in a bit of a dilemma about the best way to plumb my expansion tank on my RV8.

The setup at the moment:

Ally expansion tank with pressure cap, bottom outlet and top outlets. Note: the small top outlet does not work in conjunction with the cap (as is usual on rad caps) This tank is higher than the rad.

The bottom of the exp' tank is plumbed to the rad bottom hose.
The top exp' tank outlet is plumbed to the rad top hose.

My problem is that I have a pressure cap also on the radiator. Now I know that I should only have one pressure cap, presumably on the expansion tank.
If I was to fit a non pressure cap on the rad, then am I right in thinking I should block the outlet on the rad neck? (otherwise I would get coolant under pressure pouring out??)

At the moment I have a pipe fitted to the rad neck which goes down into a bottle as I keep losing a small amount of coolant via the rad cap pipe after a run. Problem is that this coolant does not get sucked back into the system presumably because of the expansion bottle pressure cap allowing air to be sucked in rather than the coolant from the rad bottle.

In short, do I fit non pressure cap to the expansion bottle and leave the rad as it is, or the other way round and block off the rad blow off pipe?

What I dont want is coolant under pressure being released from under the expansion bottle cap as this would finish up all over the battery and so on.
New expansion bottle with neck outlet as per rad perhaps??

Hope this makes sense, sorry its a bit lengthy

Thanks for the help

Dave

Confused? you betcha!

Post by **katanaman** » Mon Jun 18, 2007 7:12 pm

The pressure cap should be on the expansion tank. The reason your probably loosing coolant from the rad cap is because there isn't an air gap under it. I would block off the rad, if its brass then solder a plate over the hole and forget about it. After that and assuming you run a proper air gap in the header tank you shouldn't ever loose coolant. If you are then you have a problem as it should only blow if there is a fairly big problem.

Are both pipes to the header tank from rad hoses the same size? If they are then you need to fit a restrictor in the hose going to the top hose. Something like a 5mm hole should be ok. This is only to purge air out, if you don't run a restrictor the you are effectively bypassing the radiator to some degree.

dave wj · Post by **dave wj** » Tue Jun 19, 2007 7:43 am

Thanks for the reply Marki,

Yes the hose configuration from the expansion tank is as you suggest. The top hose is indeed a smaller dia than the bottom.

I'm hoping the cause of my coolant being forced out is due to what you are saying and not something more sinister. Curiously, it seems worse if I use WOT.

I think I'm giving it enough expansion room. My exp bottle is 14cm high x 10cm dia. I usually have around 5cm depth of coolant ,leaving around 9cm height for expansion purposes. Is this enough?

Thanks again for the reply

All the best

Dave

Post by **katanaman** » Tue Jun 19, 2007 9:27 am

I wouldn't worry about it as its more than likely down to no air gap in the rad. I only really pointed that out as you didn't want overflow from the header which isn't the norm. Seal your radiator cap and all should be well.

dave wj · Post by **dave wj** » Tue Jun 19, 2007 11:07 am

Thanks Marki, I appreciate your help

Cheers for now,

Dave