radiator expansion tank

[Moto Carlo]

You guys seem like the right crowd to ask a nutty question. ;-) 
I have relocated my battery to the trunk. The engine compartment battery shelf is actually welded to the body and it would make a real mess cutting it out. 
So I am thinking to use that area for an expansion tank to .... well, to expand the radiator. Anyone else done this with cooling success?

 

[esty]

the o2 does not need an expansion tank...see 

 

 

[uai]

the expansion tank only makes sense if it's above radiator level. 

[AustrianVespaGuy]

Also it's not a big deal to cut out the tray.  Only 3 short ~1" welds hold it in, took me maybe 10 min with the dremel, and then provides a great spot for plumbing your cold air intake for your EFI conversion. . . >:D

Edited July 17, 2021 by AustrianVespaGuy

[Moto Carlo]

Thanks guys..
Uai you are correct sir. The tank cap needs to be the high point in the system. But I have seen it possible to purge the system then lower the tank. There is even a system that slides on aluminum rails to do this. But this is getting to be a bit of a battle, that a larger radiator would easily fix.
Vespa guy. Again good input, but in my case it is a solid weld. Don't know how or why. I have seen other 02s with those 3 welds, but not mine. On the other hand, I am shopping an EFI, so there it is. Good idea. I will simply cool it for now, because I might need that space for the fuel injection.
Which EFI are you using?

[jimk]

2 hours ago, uai said:

the expansion tank only makes sense if it's above radiator level. 

Naw, take a look at a new car.  If the 02 radiator is completely full (running solid in hydraulics terms)  and the cap is a double seal cap with a check valve in the cap and the expansion tank has the connection at the bottom or the tube pushed to the bottom, the radiator will draw coolant in on cool down and push coolant to the expansion tank on heat up.  This is used on crossflow radiator designs, check under my hood.  Sometimes you gotta think out of the box!

[uai]

6 hours ago, jimk said:

Naw, take a look at a new car.  If the 02 radiator is completely full (running solid in hydraulics terms)  and the cap is a double seal cap with a check valve in the cap and the expansion tank has the connection at the bottom or the tube pushed to the bottom, the radiator will draw coolant in on cool down and push coolant to the expansion tank on heat up.  This is used on crossflow radiator designs, check under my hood.  Sometimes you gotta think out of the box!

That's a catch tank? Isn't it? I understand the principle but an expansion tank is in the pressurized part of the cooling system. In period there were often used early e9 tanks or half early e 9 tanks.
 

Edited July 18, 2021 by uai

[dlacey]

I have a catch tank about 1 pint capacity mounted next to the radiator on my inka car. After an hour in hot city traffic the temp gauge is ~3/4 and the catch tank is full. After cooling for 3 or 4 hours the contents of the catch tank have been sucked back and the tank is empty. Works for me...

[Moto Carlo]

My thought on either the overflow tank or the expansion tank is to add  more fluid to the system. The expansion tank being under pressure is more like a radiator extensions. As I understand it, "burping" the system when filling it with coolant requires the filler to be the high point, after the system is purged of air, it can actually drop down . Race systems do just that . The expansion tank is on a track so it can side up to fill and slide down to close the hood.

[Schon '02]

I’ve installed one and it works just the same as the one on my Alfa GTV. I keep the bottle ~1/3 full when cold. When the engine warms up, hot coolant overflows into the bottle from the bottom; when the engine cools off, it draws it back into the radiator. There is no empty head space at the top of the radiator as there would have to be without the bottle. 
 

I can check for coolant lose by just looking at the bottle for a change in level when cold (~1/3 full) or hot (~2/3 full).

[jimk]

7 hours ago, uai said:

That's a catch tank? Isn't it? I understand the principle but an expansion tank is in the pressurized part of the cooling system. In period there were often used early e9 tanks or half early e 9 tanks.
 

BMW system the tank would be called a pressurized head tank,  It serves two purposes, one for expansion volume and second as the head tank.  It is connected so it supplies coolant thru the large hose at it's bottom to the pump suction.  Those tanks also always have a slight flow thru the tank.

I know the E30s do not have a radiator cap, the cap on the tank acts as the system pressure cap.  If the radiator has a cap, the tanks are non-pressurized. 

Edited July 18, 2021 by jimk

[irdave]

Wait, what?  So can I use my pressurized head tank, the stock e30 system, just burp it above the height of the radiator, then lower it down so the hood can close?  That would solve so many of my lazy problems.

 

@jimk All the information you've shared with me, and not this part?!?!  :laughing my head off emoji

[jimk]

4 minutes ago, irdave said:

All the information you've shared with me, and not this part?

You were so quick to remove all the excess baggage, I assumed you knew all about it.  The system you have now is unique, first capless cooling system around.

[Moto Carlo]

This might be of interest.

 

[jimk]

@Moto CarloGood explanation.  I learned that there are non-pressurized caps!  Circulation thru the tank as used as an expansion tank is similar in concept to what the later BMW cars use.  Thank you.