Coolant expansion tank.

[cantfindausername]

I'm after some of your views on a little project I am undertaking while I rebuild the engine on my car. The coolant system is something that I am not overly familiar with. I get the basics, but do question my knowledge of the expansion side of it.

I am looking at changing the location of the stock filler neck, and changing the expansion tank to an alloy one.

Does the expansion tank need to be an air tight? On the stock one there is an overflow, so I can't quite see how it would be.

I will try and get some pictures posted to help explain what I mean as I don't think I've done a very good job.

Ant

[Guy Croft]

Hi

1. The header tank must be above the engine to vent air.
2. It must have a pressure cap and bleed pipe if the radiator doesn't have its own.

The purpose of the header tank is to allow easy filling and the coolant recovery back to the radiator after expansion when hot. Systems with open bleed form the rad neck where the rad carries a pressure cap lose a bit now and then and require constant topping up. A sealed header tank system with pressure cap on the rad should not lose any.

Is this a start?

GC

[SteveNZ]

There are 3 basic designs

1. Closed circuit header tank
2. Closed circuit with expansion tank
3. Open circuit.

A closed circuit header tank must be air tight and pressure regulated via the correct cap. You can get away without a manual bleed valve if the system is well designed, e.g. Uno turbo, they have a self bleeder (best system design IMO)

You can run a closed circuit with an external expansion tank. The external tank serves as an expansion tank but is not a header tank. This tank does not need to be air tight, its just a reserve tank. These are a bit more complicated but could be easier to fit. They can be fitted anywhere. This design is common on Japanese cars.

Open circuit will loose coolant to the atmosphere. They have no expansion tank or header tank. They will loose coolant and are really out of date now.

[cantfindausername]

Thanks you two, that is definately a start!

Going from SteveNZs descriptions I would hazard a guess that my car (Toyota MR2) is fitted with options 2. Closed circuit with expansion tank.

The summary seems like what is currently on the car. The expansion tank just has a plastic "pop" lid.

I will still post some piccies so you can see what the system is like, or will be like if my plan goes ahead. I also like to get your opinions on these modifications as its all new to me.

Thanks again,
Ant

[SteveNZ]

Yes, an MR2 has a closed system with expansion tank. What were you planning? As long as the tube can still pick up the coolant, you can move or alter the tank however you like really.

Make sure the radiator cap is working correctly. If in doubt just get a new one.

[cantfindausername]

The rad cap is relatively new. Maybe 2 and a bit years old. I will check it for seal though before commiting it as a part for my build.

And thanks for confirming. I'm really excited to get it all together now as see my custom modifications coming together :D

My plan for that area of the engine bay is to tidy it up a bit. There is normally a charcoal canister, this is being remove along with all the pipes for that. The old expansion tank is being taken out. This is primarily due to the fact that there will be charge pipes running through where it lives that are going to/from the intercooler will be mounted in the boot(trunk). And the filler neck will be moved to a suitable location, probaly on the rear fire wall of the engine bay. And lastely, the fuse box. This will probaly move down a little way to further down the fire wall. Again, due tothe charge pipes.