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If I have a filler with a radiator cap, like this ( https://www.summitracing.com/parts/sme-2202 ), in a coolant hose at the high point in my cooling system, do I need to have an expansion tank or can I get by with a recovery tank plumbed to the side outlet adjacent to the filler cap?

I'm thinking that if I fill it to the base of the cap, leaving no air space, expanding coolant will flow directly to the recovery tank and be sucked back when the coolant cools and contracts.

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Jerry Henneman

Jack of many trades
Master of unfinished projects
build blog/log at https://jerryslocost.wordpress.com

That will work fine, but you'll need to allow for some expansion volume in that upper hose. Try filling the upper hose about 1/2 way. If that's not enough space it will overflow to the catch tank (actually a recovery tank with the tube going to the bottom). The layout you are planning is how I ran the 13B in the Caterham.

Dodge Dakotas have those in the rad hose. Check the junkyards!

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The Lethal Locost
The Lethal Locost 2 - Even More Lethalerer

I have that exact setup in the Slotus. I've found thru trial and error (and spilled antifreeze) that it seems to work best with just a trickle showing in the upper hose at "cold" temperatures. Anything more than that just gets pushed out when the motor gets hotted up and doesn't get drawn back in.

JDK

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JD, father of Quinn, Son of a... Build Log
Quinn the Slotus:Ford 302 Powered, Mallock-Inspired, Tube Frame, Hillclimb Special
"Gonzo and friends: Last night must have been quite a night. Camelot moments, mechanical marvels, Rustoleum launches, flying squirrels, fru-fru tea cuppers, V8 envy, Ensure catch cans -- and it wasn't even a full moon." -- SeattleTom

Maybe I don't get it. Why not just install a recovery tank, fill the system to the brim and skip the expansion tank? Even with an expansion tank, I would have a recovery tank just in case.

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Chuck.

“Any suspension will work if you don’t let it.” - Colin Chapman

Visit my ongoing MGB Rustoration log: over HERE

Or my Wankel powered Locost log : over HERE

And don't forget my Cushman Truckster resto Locostusa.com/forums/viewtopic.php?f=36&t=17766

That's exactly what I'm talking about doing.

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Jerry Henneman

Jack of many trades
Master of unfinished projects
build blog/log at https://jerryslocost.wordpress.com

If the overflow can has a proper bottom feed, the system should remain completely full with no space in the hose.
You do need a cap with the upper seal that is meant for an overflow tank for it to work properly, otherwise it just spits out and doesn't draw back in.

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Planning a Duratec powered, Miata suspended 442

So no pressurized expansion tank, just a vented recovery tank and fill the engine, rad, hoses and part of the recovery tank to the brim? It worked on my Locost with a 13B engine (just like the OEM setup) . It also works on my 2015 Ford Escape (turbo) OEM design. So long as there is enough unfilled space in the recovery tank to accommodate the coolant expansion, I think you should be golden. I'm willing to listen to others opinions.

Note to others, there are differences between "expansion", "recovery" and "catch" tanks. Some interchange these terms improperly.

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Chuck.

“Any suspension will work if you don’t let it.” - Colin Chapman

Visit my ongoing MGB Rustoration log: over HERE

Or my Wankel powered Locost log : over HERE

And don't forget my Cushman Truckster resto Locostusa.com/forums/viewtopic.php?f=36&t=17766

As Chuck correctly points out, I labeled the "catch" tank incorrectly. The tank in my system was a "recovery" tank. Thank you Chuck, for keeping the info available here pointing others in the right direction.

I'm using a simple, vented recovery tank & no expansion tank. I figure that, since every car I own has that system, it should work on mine.

In my case, the radiator's top tank is the highest point in the cooling system (well, the top of the recovery tank is a bit higher, which allows for expansion & recovery...just like in my Ford Escape, Miata, etc.). My buddy (Gunner1 on this board) is using a much more complex system, with pressurized expansion tank, recovery tank, in-line bleeders, multiple temperature sensors, etc. I'm hoping my simplistic system will work as well.

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Scratch building, at continental-drift speed, a custom McSoreley-design framed, dual-Weber 45DCOE carburated, Zetec-engined, ridiculously fast money pit.

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I'm using the same simple vented recovery tank as zetec7, but my heater core is a good 4 or 5" higher then the cooling system, but with the recovery tank and the rad is lower the than engine. I use a cooling flush system connector to fill the system, and then just monitor the level gradations on the recovery tank. It takes about 3 ~ 4 heat and cool down cycles of topping off the recovery tank. Once the coolant level stabilizes, I'm good to go. Davew

This would work for a 13B or a V8, but I would be careful with an inline 4. I ran this setup for two years and burned a couple of valves in the process. The engine would heat up and dump coolant into the overflow just fine, but at some point the water level would drop below the top of the cylinder head and fry the valves. The hose just wasn't high enough and the radiator was by necessity a lot lower than it was supposed to be.

I added a 1-1/2 quart Moroso tank as high up on the firewall as it would go, plumbed the heater connections through the tank's NPT fittings, and ran the pressure cap output to the overflow. Water level cold is about 1 or 2" below the top of the tank, which is still 1 or 2" above the top of the cylinder head. Plenty of room for expansion and the overflow bottle is seldom used. Best thing is, no burnt valves in the last three years.

My recovery tank only holds 1 pint. The coolant level is run at between the 10 and 12 Oz lines, [room for expansion] You have to run your recovery hose to the bottom of the tank plus every connection and the rad cap, must be tight to prevent any loss of vacuum during cool down. The only issue is because the heater core is the higher then the engine and the rad is lower then the engine, you have to top off the recovery tank for the first 2 or 3 heat/cooling cycles to completely fill the system. No over issues, even with low drag water pump , less vanes then the standard 4AGE water pump, and its 10% under driven. My rad could be slightly larger then the stock Toyota. It was sized to fit inside the nose cone. Davew

IMHO, at the risk of repeating others, you do not need an expansion tank. A recovery tank is fine. To prevent the secondary cap from venting, use a 25psi cap. This can be either the filler or radiator, but you can use standard psi caps and tee the ports to the recovery tank. Do not leave an air pocket on the pressure side with a recovery tank.
An expansion tank is essentially an air pocket on the pressure side and does not connect to a recovery tank because the tank would fill the pocket after a few cycles if the system has no leaks (like a bad head gasket). The vent port from an expansion tank goes to the vent port on the radiator neck when there is no recovery tank. A recovery would be redundant.

I used the same filler you have on a 4.3lv6 fiero. I used the common vw round expansion tank on the GO4 interceptor with a civic radiator. https://www.ebay.com/itm/Radiator-Coola ... ition=1000

Dorman makes a good quality overflow/recovery that has enough capacity for just about anything. https://www.ebay.com/itm/Overflow-Recov ... SwWXhctIl8

Tank size should match radiator capacity. For example, I would not expect a stock civic overflow to have adequate capacity to work with a civic aluminum racing radiator, which should hold about twice as much coolant and expand twice as much to reach 200f. There should be just enough coolant in the recovery to cover the end of the hose when the engine is cold and the rad is fully filled. Anymore takes away from the capacity for expansion. Any bottle that can keep dirt out will do.

If heater hoses are the high point (like on my 5.0l 80s ranger), just use a prestone coolant flush kit that has a small inline filler to top.

You only need one cap of course and is doesn't need to be on the rad. This scion racing rad looks promising and about the same price but bigger than the civic racing rad.
https://www.ebay.com/itm/For-04-07-Scio ... 2649033004

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