Arghh...coolant problems...how tight is your cap????

[Marcus_uk]

After spending alot of time under the car i've managed to get two trouble free running in the car but thats it...

Ive just changed the head gasket (head skimmed and tested) but the car has decided to empty the coolant out of the header tank cap once it gets to about 1/2 temp on the gauge... the car didnt over heat as i drive checking the temp gauge every 10 seconds or so. This is something the car did once previously and i put it down to not fitting the cap properly (although i had only had the car a short time before i had to change the HG... the car vented the coolant on the motorway!

I had thought that the coolant vented due to HG failure, but I changed the cap just in case. Seems im still having this problem even with a new cap and HG.

My thinking is either the system creates too much pressure or the cap/expansion is venting at too low a pressure.

Has anyone had any problems with the header tank. When i tighten the cap, I can turn it until it gets reasonably tight but never get tight enough to stop you being able to turn it. It seems to go slack again as if its jumped backwards on the thread, but the cap is new and the tank thread looks fine.

I guess I need to know how tight do you guys turn your cap. Will it turn till it "locks" or is the ability to only tighten it to a certain torque built into the design to allow it to vent at a certain pressure?

A quick reply would be appreciated as I need to get the car up and running by the weekend as I have a wedding down in london to get to! I hoping its a header tank/cap issue... fingers crossed

Cheers in advance

[GeoffSmith]

It should tighten and remain tight so maybe the thread on your header tank is the problem.

[Marcus_uk]

Ive just tested the block...(paranoia is a wonderful thing) and its fine...no gases in the coolant so it must be venting at too low a pressure?

Thanks Geoff. Mine tightens pretty tight and then if you turn it a bit more it goes slack so if this isn't a design feature related to cap being able to vent above a certain pressure then im going with you on a dodgy thread somewhere.

[theelanman]

mmm...what the cap??...
IIRC there was a dilema not so long ago about finding a 'propper' fitting cap........cant remember the outcome but I do remember its only cap suitable.....

[superbad]

I had the same problem. Car had a generic GM cap that seemed to fit and even tightened up OK, but would vent coolant everywhere when it got hot. I got the Lotus cap and it's all fine now. If yours is jumping thread when you tighten it, something is definitely not right.

[Marcus_uk]

I had the same problem. Car had a generic GM cap that seemed to fit and even tightened up OK, but would vent coolant everywhere when it got hot. I got the Lotus cap and it's all fine now. If yours is jumping thread when you tighten it, something is definitely not right.

I got a new cap (a yellow one from SJ which i assume will be lotus) which replaced the black one that was on it, but still no luck. Going to try and track down a new header tank.

[Tannerman]

Hi, Marcus....As a quick bodge try putting PTFE tape around the header tank thread .

This should beef the thread up enough and the new cap will cut a new thread in the PTFE tape.

It,s a bodge but it may get you to London at the weekend.

Good luck

[bobbrown]

You should be able to source a header tank from any Vauxhall dealer GM 90128691 Nova/Corsa I think

Bob

[GeoffSmith]

Correct although some people have experienced problems with recent GM tanks that split! A scrappy might be the best option.

Oh, and the yellow cap is the latest style to help people taking a driving test to identify where to put the essential fluids - I'm certain Lotus just repackaged GM ones.

[uk08462]

Beautiful sunny day back in 2000, on the M40 returning home from work in Coventry, roof down, sun in eyes so I could not see temperiture gauge. Result, all the coolant vented from cheap cr*p GM coolant cap and the engine had fried itself. My lovely Elan completed the journey courtesy of the RAC. I still cringe when I pass the spot.

You have been warned!

[esprit888]

Also a common misconception is that if you loose your coolant in a hurry the temp gauge will send you a warning, most of the time it won’t. The temp gauge sensor is designed to read coolant, not air, if you loose all of your coolant (say a bottom hose at 100MPH) the air temperature around the sensor will rise but by the time you see it send a reading past the ‘holy sh*t’ mark on the gauge, its too late. There are numerous low level alarms that can prevent this including a universal low coolant alarm that fits in the plastic header tank. An Australian device (on ebay) reads the head temperature and is widely used amongst the ‘desert fraternity’. The simpler float devices usually go for around $50.

Beautiful sunny day back in 2000, on the M40 returning home from work in Coventry, roof down, sun in eyes so I could not see temperiture gauge. Result, all the coolant vented from cheap cr*p GM coolant cap and the engine had fried itself. My lovely Elan completed the journey courtesy of the RAC. I still cringe when I pass the spot.

You have been warned!

[Marcus_uk]

Ok the plot thickens.

The new yellow cap that I have been sent is different from the black one that was on the car (see photos)

side mini.JPG

bottom mini.JPG

The strange thing is the old black cap fits nice and tight where as the new yellow one jumps the thread once you get it reasonably tight. This could mean one of the following, your input as to which one is true is welcomed:

1) I think the yellow one jumps thread as the inner pressuere relief mechanism on the yellow one is much deeper, meaning less thread is in contact when the plunger hits the inner rim of the tank.. So does this mean there are two types of header tank? one that fits the shallower black cap on one with a deeper rim for the deeper yellow cap?

2) Ive been sent the wrong cap

3) Ive been sent a faulty cap that should grip better than it actually does (the thread looks fine)

4)Both the header and cap have been warped in someway so that they still fit together, but wont take a new straight cap

5) none of the above?

Any input would be welcome as i now dont know which cap to run with... i dont want to loose all the coolant going down the motorway again!!!

[GeoffSmith]

The yellow one looks completely wrong and I wouldn't use it. I think the deeper central section is bottoming out as the hole in the header tank is a lot smaller diameter - this most likely explains the cap loosing the threads as you try to tighten it up. If you remove the small return pipe and hold a finger over the hole into the header tank, it is possible to pressurise the system by blowing into the pipe. I think you'll find coolant p155ing out past the yellow one and maybe a trickle past the black one as the rubber gasket (which is meant to seal on the system) looks a bit sorry for itself - you could try carefully prising it out and turning it over to see if you can get a better seal temporarily.

I agree with Colin: A sudden loss of coolant doesn't necessarily show up on the gauge. When my heater valve fell apart, the temperature rose to about ¾ then start falling again - I was lucky to catch it.

[Marcus_uk]

The yellow one looks completely wrong and I wouldn't use it.

Is anyone elses yellow cap like this one? Im going to feel daft if i order another one from a different source and it turns out to be identical...

[dapinky]

Da da da da daaaaaaaaa.........


....Captain Bodge enters the fray ! ! ! !

Marcus,
there has been much discussion over the years about yellow and black caps being different - with people quoting pressure ratings and all sorts, but the fact remained, that Lotus would provide black, whilst GM would provide yellow....

...Geoff has summed up the reasons quite succinctly - anything Yellow under the bonnet needs checking before you use the car (ideal for women motorists and 17-year-old yoofs).....Ducks for cover.....

...As it appears Lotus (SJ) are now providing yellow, I'm presuming they have run out of black ones in Old Stock.

The reasons for the pressure difference was meerly reading the numbers and comparing apples with pears....

Most of us are happy with PSI and/or BAR (ATM) pressure scales (even if we can't equate them, we have heard of them), then caps started to appear with numbers which were a bit higher than expected for a water system running pressure...

...then someone actually read the small print and found that those clever people had started rating things in KPa and/or mmHG, so they were still all the same.


So - colour doesn't matter!


However, yours does look different, and that does matter (if it doesnt work because of the shape).

As stated above, try pressurising the header tank with the yellow one fitted - probably best to take it out of the car, put a hand over the big pipe outlet, and an air line on the small one (set to about 10 PSI). If you can hear it hissing as air escapes, the cap or its sealing is wrong.

If it appears okay, bump up the air pressure to 20 PSI and try again...

...and again....

you will find the specific pressure at which your cap opens to vent (before anyone too picky comes along, I know that the temperature will have an effect as well, but that doesn't matter here ).

Try again with the black one.....

This will tell you if the cap ratings are the same, or even if one/both are not sealing, or opening too soon, or whatever.

It also gives you a chance to ensure that the fault isn't in the bottle itself somewhere unseen whilst fitted (a crack at the back perhaps???).

If all appears okay with the bottle, and the cap (whichever one works) then we have got rid of a variable!

I would suspect that the problem is either in the sealing of the black cap, or in the bottle material, with the yellow not sealing at all

As Geoff says, turning over the rubber washer may get you a better seal....

but i did a temporary repair ages ago which involved cutting a new sealing washer out of a piece of neoprene sheet and coating it with silicone sealant and allowing it to dry before refitting it.
This was so temporary that it is still there 2 years later

Admitttedly, I only did it because I lost the old seal at the side of a busy road at night whilst re-filling the water bottle to limp home with HGF, and a rubber O ring and silicone didnt work very well

As such - a smear of silicone on your seal may re-juvenate it, because i expect they would cost a few pence each to get one

[HJ2]

Might i add: Check if the top of the threaded section of the bottle is undamaged / scratched?
A bad sealing is not necessary caused by the seal if the surface the seal rests on is not flat ...

[Monty]

Marcus,

I`ve got a spare used tank with cap if you want to compare or even use, it needs a good clean thou

BTW, when doing a coolant change you need to bleed the system, other wise you get an airlock and end up with the coolant over flowing the expansion tank which sounds like what has happen with your Elan

[Marcus_uk]

Marcus,

I`ve got a spare used tank with cap if you want to compare or even use, it needs a good clean thou

BTW, when doing a coolant change you need to bleed the system, other wise you get an airlock and end up with the coolant over flowing the expansion tank which sounds like what has happen with your Elan

Cheers monty, I think I might take you up on that offer. Im running the car with the black one and so far I havent had any trouble. I guess I will find out this evening when I head down south.

The bleed screw is broken on my car im afaid. So i start her up, top up the fluid then go for a short drive with the heater on... making sure it comes on hot, re-check the level (without taking the cap off) and then re-check again everytime I come back to the car when its cold. Will this be ok to get all the air out of the system or do i need to sort out the bleed screw?

[Monty]

The bleed screw is broken on my car im afaid. So i start her up, top up the fluid then go for a short drive with the heater on... making sure it comes on hot, re-check the level (without taking the cap off) and then re-check again everytime I come back to the car when its cold. Will this be ok to get all the air out of the system or do i need to sort out the bleed screw?

Yeah, i don`t always use the bleed screw.

After a coolant change i would leave the car running for quite awhile and keep releasing the cap to let the pressure out. Then go for a run and do the same thing again.

If you want to pick up my spare tank before you head south then PM me and i`ll give you my address.

[RayD]

Marcus,

Was the rubber seal fitted to the black one when the picture was taken ... or is it an illusion?

Ray