Overflow bottle a one way deal?

[Guest]

I took my overflow bottle out today and cleaned the slime out from the bottom. There was antifreeze in it but after I cleaned it, I left it empty. It's not like my Blazer where it goes back and forth correct?

 

[DNK]

The over flow on the wedge is a water bottle with the tube thru the cap.

 

[Andrew Mace]

I took my overflow bottle out today and cleaned the slime out from the bottom. There was antifreeze in it but after I cleaned it, I left it empty. It's not like my Blazer where it goes back and forth correct?

Actually, yes it does, AFAIK. I'll leave it to others to explain how it all works (thermo-syphon, perhaps?), but it should always have some coolant in it.

 

[Guest]

Thanks, I will definitly need this explained to me with small vent holes in the overflow caps in both the Spit and TR6. My Blazer overflow tank has a sealed system and that system I can understand how the back pressure works when the system cools down.

The coolant in the TR6 radiator is nice and greenie green. The brown gunky liquid in the overflow bottle was not backwashing into the radiator.

 

[DougF]

The brown gunk was likely sediment from years of not-so- greenie-green running through the system. Keep an eye on the color of your antifreeze. Should it turn brown fairly quick, assuming you recently replaced it, the cooling system may be needing a good cleaning.

 

[guzzul]

My understanding is that this is indeed supposed to be a two-way system. As coolant in the engine and rad cools, it is supposed to create a partial vacuum to draw coolant back from the expansion tank. If you have the overflow hose well fastened and always submerged in liquid in the bottle, it should work.

The pin holes in the expansion bottle cap would have to be there to allow air to escape as coolant from the rad flows into it. Similarly you would want air displacement back into the bottle as coolant gets drawn back into the rad.

 

[AltaKnight]

I agree, the key to it moving back and forth properly is having the bottle tube constantly submerged in fluid; if its waggling about in the air then it won't work.
Oh, and the tube and fittings have to be airtight with no leaks.

 

[Darrell_Walker]

Of course, you also need the proper kind of radiator cap. The ones that support siphoning back will usually have a little metal cap on the inside, that you can pull back. That lets the fluid back in as it cools and creates a partial vacuum.

 

[Aldwyn]

I agree, the key to it moving back and forth properly is having the bottle tube constantly submerged in fluid; if its waggling about in the air then it won't work.
Oh, and the tube and fittings have to be airtight with no leaks.

Ditto... you want to have your bottle filled half way so that the proper vacuum is created between the bottle and the radiator.

- Aldwyn

 

[Guest]

The Haynes manual says the pressure relief radiator cap setting is 3.25-4.25 PSI. It has a 6-8 PSI cap on it now. I don't recall seeing a PSI cap that low. I'm going to check at the parts store today put a new one on anyway. Maybe it was just my good fortune that the cap was not working properly and could not let that gunk back in the system.

 

[Geo Hahn]

I believe there are several designs on various cars for the 'bottles' in question.

Some are sealed systems wherein the bottle is pressurized and essentially an extension of the radiator. In these cases the bottle is sometimes referred to as an 'expansion tank'. My old Fiat comes to mind as a example of this.

Some (like late TRs) use a bottle in conjunction with a radiator cap that allows expansion and recovery w/o allowing air to re-enter around the cap. I think these are usually referred to as over-flow bottles. TR4 caps even had this type of cap so an over-flow bottle from a 4A or other TRs can be easily added.

Some cars use both an expansion and a recovery bottle (some VWs are an exaample).

Some radiator caps do not have this feature, most notably the stock TR3 cap. Some have modified this cap to work with an overflow bottle. Others have added a bottle that is mounted higher than the radiator neck (up around the voltage reg for example... which [IMO] looks really obvious and out of place. Other TR3 owners just use a bottle to watch overflow with no recovery.

As for pressure... I think 7# is typical for TR4 and beyond, TR3s and prior used a 4# cap. Less pressure of course means a lower boiling point but might also make life easier for you radiator.

Finally, some think adding a recovery system to a radiator not designed for it stresses the rad as it flexes (ever so slightly) to push & pull the collant out and in. Makes sense but I have no idea if such stresses will elad to a premature failure. I guess I'm conducting a long-term test of this on my 4.

 

[Keoke]

Hi Geo, No you will not experience any more stress on the system provided you do not use a pressure cap that exceeds the original design specifications. I prefer the closed system as used on the P1800 Volvo cars.---Fwiw---Keoke-AZ-- /bcforum/images/%%GRAEMLIN_URL%%/cowboy.gif

 

[guzzul]

The Haynes manual says the pressure relief radiator cap setting is 3.25-4.25 PSI. It has a 6-8 PSI cap on it now. I don't recall seeing a PSI cap that low.

That does seem very low. Your Spitifire, by comparison, would be 13 PSI.

At 3-4 psi the pressure cap would not be having much effect on raising the coolant boiling point, but I guess that's the way the TR was meant to work.

The pressure cap should have two valves in it. This was mentioned in a previous post by Darrell Walker. The centre valve opens inwards under partial vacuum to allow coolant to flow back into the rad. The outer valve is the one that has the key pressure rating.

I suppose if your rad was not full to begin with it may not overflow. Although one would think the vacuum created on cooling would still suck some coolant from the bottle back into the rad.

FWIW, mine doesn't seem to do much either,

 

[Aldwyn]

I thought Triumphs were either 6 pound (older cars) or 13 pound (newer cars)?

Is this not the case?

 

[guzzul]

That is the case for Spitfires at least. Up to Mk 3 was 7 lbs, Mk 4 and 1500 are 13 lbs. I wasn't sure about TR's.

 

[TR3driver]

Radiator cap pressure varied for various Triumphs and across various years. Lowest I know of is TR2-early TR4 with 4 psi nominal. Highest I know of is late Stag (and maybe TR7 ?) with 20 psi.

Early TR6 was 7 psi, later TR6 was 13 psi.

Adding a recovery system to a system not originally so equipped probably would increase stress on the radiator *very* slightly, since the radiator will see slightly more vacuum when it has to lift the water up from the level of the recovery bottle. But this is trivial compared to the pressure differential it sees in normal operation anyway, so I can't see it as being a problem.

BTW, late Stags have the pressurized bottle as Geo mentioned. I now have one of each, since my second Stag has been converted to the later cooling system.

 

[DNK]

My 8 has a 15 lb'er