Coolant catch tank

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Jerryedmans
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Coolant catch tank

Post by Jerryedmans » Mon Aug 05, 2019 12:29 pm

I've been worrying about coolant levels. Cooling system built as per Hawk manual using Gerry's header tank. But when the engine is run there is expansion and coolant drains out of overflow tube. Hence after a few journeys, when you take the cap off the header tank the water level is much lower and sometimes hard to tell if anything in there leaving me worried that I might be setting off without enough coolant and a possible overheating problem, although in fairness it has never overheated even though the header tank appears almost empty most of the time.

Anyway I have bought a coolant catch tank and was about to fit but just scratching my head and wondering if if will be of any use.

My thoughts are that the coolant will drain from the filler cap overflow into the catch tank. But when the engine cools, surely the filler cap overflow is a one way valve? I.e as soon as pressure reduces the radiator cap will seal and so the coolant that overflowed into the catch tank will not get sucked back but will stay in catch tank so not a lot of point of having the tank? Is this right? Presumably this would leave a vacuum in the coolant system after the first drive and expansion - correct or can air / water suck back in through the overflow valve?

Hoping someone else has a better understanding of this and can advise if worth fitting or not.

Cheers

Jerry

KevinW
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Re: Coolant catch tank

Post by KevinW » Mon Aug 05, 2019 12:35 pm


Jerryedmans
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Re: Coolant catch tank

Post by Jerryedmans » Mon Aug 05, 2019 7:46 pm

Thanks Kevin - YouTube video perfect - I now know how it works - had not realised the radiator cap had a 2 way valve system.

I bought an 800ml expansion tank. Which one did you go for and in your experience is 800ml adequate?

Cheers

Jerry

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clive
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Re: Coolant catch tank

Post by clive » Mon Aug 05, 2019 9:07 pm

HI Jerry,

I have a Ford 302 with Gerry's expansion tank fitted. My car has done over 40,000 miles in thirteen years and has never given me any serious heating issues even in temperatures of 38 degrees. When cold, the level of coolant in the expansion tank is approx half full and level with the inlet/outlet hoses. As far as a vacuum being formed, I don't see how that would occur as when the coolant heats up, it expands and pressure increases until it reaches the pressure of the radiator cap, and when it cools it decreases in volume back to the original and the pressure will drop to what it was originally and not less than atmospheric.
Cheers, Clive.

(If I'm not here I'm in my workshop or on the golf course!)

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Re: Coolant catch tank

Post by CobStang » Mon Aug 05, 2019 9:43 pm

Couple of pointers.
For the system to recover water from a header or catch tank you must have a double seal cap.
The stub on the filler neck that the recovery hose attaches must not leak air, a lot of these stubs just screw in on one or two threads, they leak air.
If you want the system to work properly get someone to TIG weld the stub to the neck.

KevinW
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Re: Coolant catch tank

Post by KevinW » Tue Aug 06, 2019 7:53 am

Jerryedmans wrote:
Mon Aug 05, 2019 7:46 pm
Thanks Kevin - YouTube video perfect - I now know how it works - had not realised the radiator cap had a 2 way valve system.

I bought an 800ml expansion tank. Which one did you go for and in your experience is 800ml adequate?

Cheers

Jerry
Hi Jerry, Mine is the 750cc tank in the link, mounted at the bottom of the wing near the chassis rail, out of sight. It all seems to work.
However, my big fix was when I installed a 12psi pressure cap - my engine builder used a 6psi cap, and it always boiled over before replacement.

peterc
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Re: Coolant catch tank

Post by peterc » Tue Aug 06, 2019 10:21 am

Hi Jerry,
Writing this for the third time so hope it loads properly this time.
Place a spirit level across the engine bay to check where the highest point is. In my case the heater was higher than the top of the header tank and I suffered the same issues as yourself.
I now run with a plain cap on the header tank and a pressurised cap on the over flow tank in the form of an old Austin Metro unit which is connected from the header tank overflow pipe down to the bottom of the overflow bottle.
I now have a water level at the very top of the neck of the header tank rather than the 1.25” lower when running an open system.
I have just replaced my water pump and it takes 2-3 heating ups to regain a stable level at 1/4 full in the over flow tank.
Best of luck.
Peter C
Last edited by peterc on Tue Aug 06, 2019 6:41 pm, edited 1 time in total.

allan horsfall
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Re: Coolant catch tank

Post by allan horsfall » Tue Aug 06, 2019 10:45 am

Looks like Peter and I are having the same trouble!

I run a Rover engine and initially had the same problems, I made 3 changes.
1) I raised the header tank to be the highest point in the system. It is after all a 'header tank'
2) I fitted the fan switch to the radiator inlet hose, on the basis the outlet side is to late. Its purpose is to monitor the heat of he engine not the radiator.
3) I reworked the nose cone air cowling to ensure all the air went through the radiator. Probably the most important factor.

Now runs like a dream no heating problems at all.

peterc
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Re: Coolant catch tank

Post by peterc » Tue Aug 06, 2019 12:33 pm

Agree with Allan on the ducting in the nose area. I added a baffle to block off the gap over the top the rad. Now the air to goes through the rad instead of over it.
I added my overflow tank over 15 years ago and it has worked fine since.
The basics of having enough expansion space for when the water is hot still applies. If the spare space is not there then the water spills out which on an open system is onto the road.
Peter C

stu60
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Re: Coolant catch tank

Post by stu60 » Tue Aug 06, 2019 7:57 pm

Hi
I have also experimented with sealed system overflow tank.
- i agree the outlet pipe from Gerry's header tank was not airtight (it was never designed to be) so unless you're lucky it will need welding up before fitting pressurised overflow tank.

- do you have any pictures of the radiator cowling as improving the airflow would seem to be the best mod.

thanks in anticipation
Stuart

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