Mk10 header tank questions

Ok, what you guys are missing is that there are two kinds of caps, irrespective of pressure ratings. For my system to work, you must have a double-gasketed style cap, which allows the coolant to be sucked back in. Look closely at the photo and you willl see. My system works - the radiator is full to the brim after cool-down.

As to the pressure rating, I’ll run a 7lb cap on an old system, as it stresses the radiator less. A 14 lb cap will raise the boiling point by about (7lb x 2 degrees/lb=) 14degrees, so is desirable. On the Mk10, I will be going back to a 14lb system when my radiator is recored - my radiator guy has condemned the radiator as being repairable, but brittle and likely to fail again soon.

I do not understand how the coolant can be sucked back through a pressure cap. On my 3.8S I fitted an MGB expansion tank under the LH fender. This has the pressure cap but the radiator neck has a blanking cap only. You still need a high point in the system to fill it initially.

Look carefully at the two caps. Yours has one gasket and won’t work. Mine has two. If still in doubt, drop by your FLAP store and the guy at the desk can explain it to you. It’s a very common arrangement.

His setup will work, trapped air would collect in the radiator cap and be forced down to the expansion tank. Excess is then vented out to atmosphere, air first.
For an atmospheric recovery tank a cap with two gaskets (combined pressure cap and total-seal cap) and some suck-back-function would be needed, where excess fluid is sucked back in when needed, via the fitting on the side of the filler neck.

As I look more carefully at your system, your plastic tank is working as a header tank, not an overflow tank. I’m not sure that I would want to trust pressure on the plastic tank, but it seems to be working for you - should the tank fail, you will be running an unpressurized system with a lower boiling point.
If you were to put a double gasket cap on your radiator, you should be able to leave off the pressure cap on the plastic tank and use it as a burp tank. I think your system would be stronger, as you no longer rely on the plastic tank staying under pressure, you can probably use a stronger cap, and you would still maximize the effect of your radiator by keeping it full.

John’s is exactly the system I described. Austin = MG = BMC and British Leyland

It worked on millions of British cars throughout the 1960s and 70s :grinning: :grinning:

That’s not to say there aren’t other systems that also work …

I noticed this car , seems to have what you are intending, several good pics

Thanks, Tony. Yes, I saw that one - it fits better on a non-ac car. I’m not any more sure that it’s original than the one I already got - I have come to agree with you that my e-bay one is probably not. My conclusion is that I will put anything I want on the car, and it will be a burp tank that functions like the one you are showing. For now, I’m waiting on a radiator rebuild, as my local guy condemned mine as being repairable, but brittle and prone to future failures. I’ve ordered parts to build a new header tank, and will send you photos when it’s complete, likely at least a month.

Hi Ron,

Merry Christmas!

Have you made progress on your new build header tank? My car has the exact same header tank and mine is similarly rusted and beyond repair. I’d love to see what you’ve fashioned and/or a parts list of what you ordered to make it if you had that by any chance!

Regards,
Douglas

Douglas,
Yes, I built the tank and it came out great. It’s at my friend’s house, the retired radiator guy who will match up the ports to the new radiator he is building for me - so it’s not yet installed. He works outside and gets to stuff when the weather is nice and he feels like it, but I should have that soon. I’ve finished rebuilding the front suspension and brake components, and I am starting to reassemble the rear suspension. I’ll put some photos of the header tank together later in the day, as well as a materials list.
Ron

2 Likes

Douglas,
I decided to build the tank in aluminum rather than stainless since the fittings were harder to find in SS. I liked the original design, lying on top of the radiator - the later separate tank might be simpler if you want to use a different radiator design.
As you can see, I got all the loose parts I needed from Speedway Motors. The plate was from a local welding shop who sheared the 3/16" bottom plate and the 1/8" top piece to my pattern. I emulated to original design, taller on the right than the left. I have a heavy duty box/pan brake and bent the top piece to a channel shape - you could get a local sheet metal shop to do that for you. I flattened the legs with 80 grit paper stuck to my tablesaw for a good TIG fit. The end pieces were cut on a band saw, and I added the holes with a hydraulic punch from Harbor Freight. A step drill could easily be used - make the hole before cutting the end piece from stock. I VERY carefully cut the tubes to specs on my chop saw - very slowly with an eye on fingers - there are safer ways.
Details - be careful of bonnet clearance - you only have an extra inch for the fill tube, and you will be a bit taller than stock with these pieces. The fill tube should be as high as convenient on the tank, and the left outside tune as low as possible. If I made another, I would notch the bottom plate to allow better TIG access to the bottom of this left tube - it was tough, even for the expert I got to do the welding. Use the original to transfer the holes to the new bottom plate before you weld.
Total cost of materials and hired labor was about $300.


2 Likes

Ron,

This is fantastic workmanship! I’m really impressed. All of your meticulous details and description are going to really be of great help to me. Thank you so much for sharing the build in such detail! I completely agree with going the aluminum route. It makes welding a bit trickier (I can’t TIG weld myself) but easy enough to hire someone after I’ve prepped all of the pieces just as I want them. Did you use 6061 aluminum? Oh and one other question off the parts lists, the 6" x 1.25" and 1.5" aluminum tubes I take it one leads to the cap and the other is the barbed fitting leading into the radiator?

I don’t own my own brake right now but am always looking for an excuse to add a new tool to my collection. And a new Harbor Freight opened up just 5 minutes away from home. The closest one used to be about 40 minutes away so this new one is a dangerous temptation! I don’t go near their jack stands but I find a lot of their tools are really quite decent, especially for the relatively light use I give them.

My radiator is original but, knock on wood, not leaking and not in too rough shape so my intention is to use it for now with dreams of a custom aluminum radiator down the road when finances allow!

Thanks again for these details and photos–really appreciate it!
-Douglas

yes, be sure to use a weldable aluminum, something in the 6000 series. Yes on the question about the tubes, although I don’t remember at the moment which was which - mine is off-site.
I would not waste my money on a Harbor Freight brake unless you want it for little pieces of 20 gauge or lighter material. You should get a local shop to make those bends in the 1/8" aluminum. My 4’ brake literally weights a ton.
Your old radiator should get you by as a local ride for awhile if it’s not leaking. My expert friend points out that they become quite brittle with age and are prone to failure, so handle gently and keep an eye on it. I’d probably stick with a 7lb cap if you cool ok with it.
Good luck, and please send a photo of your tank when you get to it.

1 Like