Rad Cap Leakage

[edcrawford]

After excellent advice from people on here I have recently fitted an overflow bottle to the rad on my early +2 to try and put a stop to the water spilling out of the overflow pipe every time I came to a stop and pretty much draining the radiator. The water now flows into the bottle but when this is full it is now spilling out of the cap! Have I got an incorrect cap on or is it going to be something more ominous. I believe the present cap is 10lb and looking through the manual It appears It should be 7lb, but would this make any difference?
Any help would be much appreciated especially if it's nice and simple for a mechanical dummy
Cheers, Ed

[tdafforn]

It should be draw back into the radiator will the coolant cools back to ambient.
May be something to do with design of the cap I guess..
Tim

[TeeJay]

Hi Ed.

In my Lotus Workshop Manual it states that all cars are now supplied with a 10 psi cap, instead of the previously fitted 7 psi one. This increases by 5 degree C the coolant boiling points.

Also the bottle should be filled with 1 pint (UK) of coolant. The tube must be an airtight fit on both the bottle and radiator. The tube must reach the bottom of the bottle and must be cut off at an angle of 45 degrees to allow free passage of the coolant.

I have checked mine on a 1968 +2 and it is as above. The bottle does not have a screwed cap but has a tight rubber fitment. I can post a photo of the bottle if it would help?

[RotoFlexible]

From the ever-helpful Dave Bean catalog:

These [coolant recovery type] caps are like any other radiator cap except they are designed with a secondary seal to prevent air leakage into the radiator around the top of the cap. This confines the vacuum to the overflow tube, which siphons back the coolant that escapes into the recovery tank when it was hot -- thus excluding air from the cooling system and maintaining coolant levels at all times. Two pressure ratings are available: 7-12 PSI (for those who subscribe to the theory that higher pressure overstresses the water pump seal) and 13-17 PSI (for those who want the higher boiling point).

This cap, along with a recovery bottle, are on my shopping list. Without the cap, it would appear that you are pumping water out of your cooling system into the bottle, and replacing it with air drawn in past the cap.

[cliveyboy]

To put Dave Beans advice into simpler terms:-
Use a radiator cap that has the rubber gasket under the lid to seal it to the radiator top instead of a metal seal.

You could even put a thin piece of rubber around the rim of the radiator top and seal the cap down onto it.

Clive

[Bob]

Hi All
This is an old cherry but I think worth bringing back up. Like most people I have had my fair share of overheating problems, 3 o'clock Friday afternoon on the Brussels ring road with the gauge reading 212 degrees I was near to panick.

I have a recored radiator, new Kenlow fan new water pump etc, I was going down the David Craig route aswell, but then I found a post that pointed out how the system worked and without a vacum seal it does not. So I have the seal now under the lip of my rad cap. I made it out of the sucker off a stick in rear view mirror I dropped and broke. 886 miles in France over a weekend 160 degrees all the way in traffic at stand still never more that 185 degrees and no loss of water. Monday in traffic jam on the M1 for 20 minutes normally I would have pulled to the hard shoulder to cool off, no 185 degrees was all it got up to.

So before you go off buying posh radiators make sure you have a radiator cap that seals and creates the vacum.
Bob

And whoever posted the photos, I cannot find the post, many many thanks.

[oldelanman]

A recovery cap is fundamentally different from a standard cap in that it has a valve in the centre which opens when there is a vacuum in the radiator to allow the coolant to be sucked back from the recovery bottle. A standard cap will only allow coolant flow in one direction so will not work with a recovery bottle.

[miked]

Just a point, the tube in the recouperator bottle is not an air tight fit. It has to push and draw air as it moves both out and in. See my set up. Bottle shown when car is cold. When warm it expands to the top green mark. Then when cool draws it all back to the same point. I have read the statement before in the manual and it does not make any sense to me. The seal on the cap tube needs to be A1, as does the cap top outer seal. Pushing it out is no problem, the trick is to have a good seal to draw it back into teh system. Hence recent talk about fitting a rubber washer to the outer part of the cap. Mike

PS pushing lots of coolant out can be caused by trapped air. Air lock! However you would not get far without overheating and squirting it out.

[JJDraper]

All comments re rad cap seal are correct. When the system works correctly, the coolant expands and pushes past the cap into the bottle (doesn't matter what psi/temp the cap is - a liquid is incompressible, so when it expands...). After a while, if the cap is at the top of the system, such as with one of mods that put the cap on or near the thermostat, all the air will be purged from the system. The recuperator bottle then shows the expansion of the coolant with a 'hot' and 'cold' levels. When the system has settled down, do not fill the system via the rad cap, use the bottle and the fresh coolant gets drawn into the system. Critical points are no air leaks on the tube to the overflow pipe on the rad cap housing and using the correct sealing cap. With the system now full of water and NO air, it works a treat, as Bob says. Heater works too! I rarely take the cap off and when I do, it is always full to the brim, often accompanied by a gurgle as coolant flows down the expansion pipe back into the bottle. This also why the bottle is always full of rusty gunk as there is a constant exchange of coolant between the bottle and the engine - see my thread on side stream filtration some years ago...

elan-f15/cooling-system-robustness-improvements-t21159.html

If you are not convinced, sit down, close your eyes and carefully think through a heat/cool cycle on the engine and what happens to the water/pipe/bottle and where problems can creep in. If nothing else, you'll nod off and wake up refreshed!

Jeremy