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MG MGB Technical - Expansion tank pressure cap

I'm retrofiting and expansion tank to my 67 B in preparation for the drive from California to MG 2009 in Breckenridge Colorado. We are driving across the Nevada desert and Utah desert on Hwy 50. It will be very hot, probably in the 100s. The expansion tank uses a 15 lb pressure cap as opposed to the standard 7 lb cap. Any reason why there is an increase in the rating of the pressure cap on the expansion tank, and where can I find a cap to put on the radiator without any pressure cap.

Thanks

Andy
67 B
74 B GT
60 A Coupe
Andy Preston

Andy, as you crawl through your local scrapyard keep an eye out for Volvo 240s, they had a system similar to the one you are assembling,you might snag the junk parts for fittig before buying new ones, just a thought. RIC
RIC LLOYD

Andy. The MGC, if I remember correctly, used a blanking cap on the radiator and an expansion tank having a pressure cap. The higher pressure cap used on the rubber bumper cars was to raise the boiling point of the coolant due to the hotter running engines after all of the pollution control devices had been installed. A hotter running engine was also deemed superior from a pollution control effectiveness standpoint.

I have never used an expansion tank on my 68GT, nor have I found any need for one. That at temperatures above 110 deg F.

Les
Les Bengtson

Andy - there are a couple of ways you can proceed with the external expansion tank. One would be to put a blanking plug on the radiator filler as Less suggests and a 7 - 15 psi pressure cap on the external expansion tank. Make sure to use good clamps on the overflow hose going from the original filler neck on the radiator to the external expansion tank as this hose will have to hold whatever pressure that cap is rated at. The other way would be to use the blanking cap with a vent hole drilled in it on the external expansion tank and put the pressure cap on the original filler neck on the radiator. This then uses the external expansion tank as a coolant recovery tank, which accomplishes the same purpose as having an external expansion tank, but without having to deal with a pressurized line going over to it (which the over flow tube from the original radiator filler neck was never intended to do). See the article, Expansion Tanks, Coolant Recovery Systems and How The Cooling System works in the Other Tech Articles on my web site at: http://homepages.donobi.net/sufuelpumps/ Cheers - Dave
David DuBois

Dave, many thanks for your very useful and well written article on coolant recovery systems. It answered all of my questions, although it makes me wonder why the factory installed expansion tanks on later MGBs and Midgets as opposed to a coolant recovery system that performs the same purpose but without pressurizing the tank and tubing. BTW don't you hang out on the MGA site as well.

Andy
Andy Preston

Andy - "it makes me wonder why the factory installed expansion tanks on later MGBs and Midgets as opposed to a coolant recovery system that performs the same purpose but without pressurizing the tank and tubing." If I had to guess, I would say that it is a difference in approach by different manufactures. From my limited perspective, I have noted that European car makers seem to favor external expansion tanks, while cars built in Japan seem to mostly have coolant recovery systems and since I have not purchased an American car in over 30 years, I don't know which they favor - different strokes for different folks.

I do monitor the MGA sites and comment periodically if a question pertains to something that I know. Cheers - Dave
David DuBois

Dave, many thanks for your help and advice. I fitted a late model MG Midget expansion tank, which fits very neatly in the inner fender well. I've plumbed it in as a coolant recovery tank but can change over to a pressurized expansion tank if that works better, by just swapping the pressure caps.

Many thanks

Andy



Andy Preston

Andy - I think that you will find that using the tank as a coolant recovery tank will work just fine. Cheers - Dave
David DuBois

Andy,
I'll second dave...I fitted a coolent recovery system (based on Dave's article) when in Boise ID...routinly 100+ in the summer with 5000' altitudes and higher...system worked wonders...didn't have to fill or top up all summer...
Bob Doc
Bob Dougherty

Can some-one help me before I use a drill and clear out a plastic pipe on an expansion tank.! MG Midgget 1500cc 1979. I blew a heater water pipe and found during the repair my radiator expansion tank was blocked. Previously checking the water level I was conned and it looked as if I had OK water level in the system. All the time it was only the expansion tank and the water wasn't moving to the radiator. The expansion tank was full of rust and contaminated water. I cleaned it out. I put a rod down the small plastic inlet pipe on the expansion tank and it is blocked. I thought drill it out and clear it. But there might be a valve in there. Then I though well why, as the water has to flow both ways. Can someone tell me if the inlet pipe to the tank should be clear. There is a pressurised radiator cap on the expansion tank but this didn't get the oppoutity to work as the pipe blew instead. Help?? Thanks.
Paul Allen

No valve, just a plain pipe from the bottom of the expansion tank to the top of the radiator.

If it is plastic be careful using a drill, you could come out the side. On my V8 metal tank the pipe goes into the tank at the top but then goes down inside to near the bottom. That involves a bend in the pipe so I couldn't use a drill to clear it anyway, so would use a length of steel wire to try and poke it through.
Paul Hunt

This thread was discussed between 11/06/2009 and 02/07/2009

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