My car is based on an MX5 donor, and I've just ordered a VW Polo radiator for cooling (mainly due to physical size). I'm trying to figure out where the reservoir connects. On both the MX5 and the Polo the reservoir seems to connect to the radiator itself, but somehow I've managed to order a rad that doesn't have a connection for the reservoir.

I'm assuming that the reservoir just needs to be the highest point of the system and can be connected anywhere, is that correct? I plan on reusing the donor reservoir. Physically speaking the heater loop is in the best place, and as I'm not using a heater would it be effective to plumb the reservoir into that loop of pipe?


Edit: OK, I've just looked at the diagrams again, it's only the overflow (?) pipe that comes from the rad to the reservoir. If the polo rad doesn't have this overflow connection, what do I do instead?

[Edited on 14-6-23 by Slimy38]

OK, I think there's more to this than I thought, hopefully someone can confirm. The MX5 coolant reservoir isn't pressurised, it's just an overflow tank. The pressure is controlled by the radiator cap, with the tee junction off to the reservoir. If I plumb the MX5 reservoir into the Polo radiator, the reservoir will just open and I'll get an engine bay of hot water.

I think what I need to do is use a pressurised reservoir instead, to match the radiator. Is that correct?

Context: I have a Mazda MX-5 engine. It's a 1994 1600cc unit with the 5 speed gearbox. I also have the VW Polo radiator.

I picked up a cheap overflow tank from eBay. The main connection on the bottom of the tank is plumbed in, via a T-pipe, to the lower pipe from the radiator to the engine. There is also an overflow, from the top corner of the radiator, into the neck of the tank. You can see the overflow pipe in the second picture.

My VW radiator has no cap or filling point on it.

I have no heater now - I did have and you can see it in the first picture. Now I have connected the two pipes, from the engine to/from the heater, with a section of rubber pipe just to close them off.


MX5 engine in situ & ready


VW Polo rad - check!

That's really useful, thanks. So it does need a proper tank. That's a clever placement, most pictures I've seen have the tank (of whatever type) sat on the bulkhead. Given the two pipe connections are at the rad end and that you have your heater in the 'usual' place yours does make sense.

At least initially I am looking at looping the heater connections, but I'll definitely keep your design in mind if I want to fit a heater.

polo cooling
from
https://7zap.com/en/catalog/cars/Volkswagen/Polo/Polo%20Classic%20%281996%20-%202003%29/SnBCVVFidmsxaERicjM1SHBjcEtQUT09--/10102-%3E10473-%3E10888/887 72|---coolant+cooling+system/

polo cooling

I'd go for a pressurised reservoir (VW globe one?) System rather than the MX5p system with unpressurised overflow.

Mount it so the "min" level is higher than any other point of the system. Plumb the bottom (larger) outlet to T into the bottom hose (top hose will do if bottom not possible) then the bottle top/bleed pipe to the bleed pipe on the Pole rad and T any other engine bleed pipes into it.

quote:

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Originally posted by adithorp
I'd go for a pressurised reservoir (VW globe one?) System rather than the MX5p system with unpressurised overflow.

Mount it so the "min" level is higher than any other point of the system. Plumb the bottom (larger) outlet to T into the bottom hose (top hose will do if bottom not possible) then the bottle top/bleed pipe to the bleed pipe on the Pole rad and T any other engine bleed pipes into it.

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I did mine (Pinto engined) with the old-fashioned, unpressurised system. As pressure rises, the radiator cap releases it to an unpressurised bottle and the cap reseals. The connection to the bottle is at the bottom (or going through the top, down to the bottom). As the system cools, pressure drops and a vacuum is formed, which sucks the coolant bank from the unpressurised bottle, into the radiator.

It is simple and effective. No, it is not as "fill and almost forget" as a sealed system, but for normal kit-car use, I have not needed to top up during the year.

You just have to have a radiator with the correct pipe connection on the side of the filler and a radiator cap that is designed to relieve one way, but allow easy backflow - as they almost all would have been decades ago.