I'm putting a Honda k24 into a 1970 Porsche 914, which originally had an air-cooled engine. The Celica radiator I'm using has a little nipple for an expansion tank. The k24 has a water filler neck that also has a nipple for the same purpose. The filler neck at the engine will be the highest point of the system.
should I run 2 expansion tanks? Or should I cap off one of them? Will a rubber cap with a clamp be enough to hold the pressure of the system? Is either location the "better" spot to put the expansion tank? I'd prefer the tank go in the frunk for packaging purposes but I can make either or both locations work.
Cap the one on the rad. I use silicone nipples for this purpose. The beefy multi- ply caps.
The one on the engine has a rad cap so it won't be under pressure to the overflow. The one from the rad will always be under pressure so you would need a pressurized overflow catch can.
I see now that the engine-side nipple appears to be threaded in. I can probably remove the nipple and plug it easily.
edit: didn't see the previous response ^
A cap like this:
https://www.amazon.com/gp/aw/d/B083QJNZDZ?psc=1&ref=ppx_pop_mob_b_asin_title
I'm gonna bring this thread back up. My coolant filler neck on the back of the head might end up not fitting in my space. In which case, I'll be changing that elbow to a slimmer design with no filler neck/cap.
if I do that, would I be able to plumb this overflow tank from the rad and be ok?
Personally, I'd make sure the overflow is at whatever end higher, and use the lower end for an air bleed.
That's the way MR2s did it. Toyota even gave you a little hose with the car to stick onto the radiator's bleed when filling the system.
Toyota Yaris has an coolant elbow that has a filler cap that's available for like $12 on Amazon.
Rock auto has plastic ones for like $8.
I would run your engine line UP to that and then have the coolant line run forward. I would attempt to replace whatever is in the front with all plugs so it doesn't vent or even have a hole in it. You can put a manual vent on it to bleed it though.
The 360 the radiators are just fully closed and below the engine. Once it's bled it works fantastically. I don't need a vent on the radiators as they are oriented in a way that they vent into the lines.
Another option is to maintain both but use a Subaru radiator cap (as opposed to the expansion tank cap which is a traditional pressure relief vented cap) which is a one way only cap that will never vent. It will only allow coolant back in but not out. They are kinda hard to find though, like I think you can only get them from Subaru as a OEM part so they aren't cheap, I have not seen an aftermarket one that I am sure functions the same way.
2 regular caps doesn't work well. I run 2 caps on the MG and the lower one is 24psi and the upper is 14 and I still run into venting issues on that.
