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Boil over when switched off


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After a three year restoration I have finally got my 1973TR6 mot'd and back on the road. I am obviously keen to use it as much as possible now we have some nice weather - but I have a problem. Twice in the few times I have run it, it boils (?) over when switched off. The overflow bottle overfills pouring water onto the ground. The first time was a substantial amount, probably because I had too much in the overflow bottle to start with. The second time not so much, but still an overrflow.

 

When running the temp shows normal and there is no suggestion of overheating. The restoration included new radiator, radiator cap, water pump, thermostat, hoses, temp sender, temp gauge re-built and calibrated, etc. Good antifreeze solution used.

 

The car was inherited as an abandoned project. PO had passed away. I have no history of the engine but I believe it to have been rebuilt. It certainly looks like it.

 

It has been suggested to me that there may be air trapped in the system that needs to be bled out. I am puzzled as the fill point (radiator cap) is lower than the top hose, so how can you get all of the air out?

 

Is this a common 6 problem with tricks to overcome it that I am not aware of?

 

I don't really want to use the car too much till I have this sorted in case of engine damage.

 

Please advise. All help appreciated.

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My rad blows out maybe 10cm which returns when the engine has cooled. If I had your problem I'd try removing the thermostat to see if the overflow is cured. If so, then fit another stat with a summer rating. Or drill a bigger hole in it as a bypass bleed.

Peter

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You do not need ramps or anything to vent the car ( if everything else is ok ) Remove the cap,have top up water with antifreeze ready,start the car and let it build up to temp keep it going and water will over flow then as it goes top up replace cap and your done

 

Edit

Make sure the heater valve is open

Edited by ntc
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Thank you for the replies.

Neil, sorry but I am not entirely clear. With the cap off and engine running up to temperature should I be seeing an initial overflow, then it falling away, to be topped up?

 

PHIL

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Perhaps stating the obvious, but make sure the pipe into the overflow bottle is pushed to the bottom of the bottle. It's held by a rubber grommet in the lid. The bottle only needs to be 40% full of coolant when cold.

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Have you done a retighten of the head bolts after the initial go?

I'm sure I did in my first head gasket on the 4A after the refurb because of this, and an overflowing water catch bottle was a constant part of the experience.

I retightened the new one after a few runs (tappets off) and radiator overflow hasn't been a problem.

One of many possibilities on the list I guess.

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Have you got the correct depth cap on the rad, it may say the right poundage but some modern ones are too shallow so spring is not compressed and actual poundage is way too low. If purchased from one of our main suppliers then it should be ok but easy to try another one first.

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Never had my 6 boil over in all the 40 something years I've owned it!

 

My 4.2 E Type Jag used to though, until I cured it with a higher psi Rad Cap!

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Hi Phil,

I had a similar issue so have a couple of tips to add.

Firstly yes is odd design that rad cap is lower than top hose. So on initial fill you can have problems with air-locks.

 

A problem with my setup is I noticed that the thermostat had no 'bleed hole'. that is either a small hole in the plate of the stat with a small drip shaped float that seals it once water reaches there. Or alternatively just a very small hole drilled into the flat plate of the stat - circa 1mm dia (i.e. enough to let air bleed through, but small enough to not allow any appreciable water flow through)

The original stat as it was had no bleed at all and when cold and closed, it sealed so well that I had a complete air lock.

 

Other tip, when filling the system, have the heater tap open, but also loosen off the rubber hose from the tap. Fill the system as normal, then start up. As engine runs ease off this rubber hose to bleed out any air from the top of the head. once you get water out of the tap from the head you know its full and push the hose back on again and secure when done.

You may have to top the radiator up a few times to fill the system completely.

 

I agree you should not drive the car too much until you have this boil over issue sorted. It should not do that.

As others have said overflow bottle should be around 50% full when cold, which will increase with a warm engine to circa 75%-80% full due too expansion.

 

Good luck. and enjoy the TR6...

Cheers,

J.

Edited by jamesStag
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Give the engine cooling a good flush. This happened to me several years ago and I undid the drain on the side if the engine block and nothing came out. Much prodding and a gush of gunk came out. Clearly the engine was not getting enough cooling as it was blocked. Get a high pressure hose and squirt in the side of the engine.

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Give the engine cooling a good flush. This happened to me several years ago and I undid the drain on the side if the engine block and nothing came out. Much prodding and a gush of gunk came out. Clearly the engine was not getting enough cooling as it was blocked. Get a high pressure hose and squirt in the side of the engine.

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Thank you all for the advice.

 

I did try to run the engine up to temp with the rad cap off, waiting for the level to fall, but as soon as the thermostat opened coolant gushed out of the rad big time - not to be recommended............ but I suppose it proves the water pump is working!

 

I have ordered another new thermostat and rad cap from Rimmers just to rule these items out. Their picture of the thermostat does not show an air bleed hole in the flange, I called them for clarification. It appears their stats do not have a bleed hole and they tell me the original Triumph illustrations do not show a bleed hole. Does not seem right to me as surely this will trap an air bubble beneath the stat when filling?

 

I appreciate a respondent mentioned he had this problem. Peter also mentioned drilling a bigger bypass hole, which rather assumes there was a small one in the first place.

 

PHIL

 

 

 

 

 

 

 

 

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Neil. Me do listen, you no explain properly - I was not expecting a one litre gushing torrent of hot bubbling overflow water before I could get the cap on to stop it......... It did not look like it was ever going to stop on its own - not before it had emptied the rad anyway. Stemming it when I did, it still took me two hours to clean up the mess in the engine bay after the fan threw it everywhere, including over me!

 

There has got to be a better way. I am sure this was not part of Triumphs design intent.

 

 

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Phil

I had same problem last year (boiled over when switched off). The radiator cap fitted was 7psi. Fitted the 13psi, problem gone.

Alan G (71 TR6 PI with original engine).

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Just checked and I have no hole in the thermostat. Yep Last rebuild a loose clip on the top hose dumped water at 82 every where when the stat opened not fun! I just top the rad up and leave the cap off till it stops bubbling and before the stat opens put the cap on. I put about 3/4 in the overflow bottle and over the next few cycles of hot cold it moves to 1/3 and stays that way. It definitely goes into the engine, I vaguely remember someone suggesting the rad cap has two parts/functions one pressure when running and one vacuum to refill when cool, just a thought?

Smoggy

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Or as good old Wiki suggests

Look at the bottom of your radiator cap. There are two seals. One that seals at the top neck and one that seals at the bottom of the filler neck. As the fluid heats up it expands. It eventually over powers the primary spring in the radiator cap.

The bottom seal is broken as the pressure exceeds the spring force of the cap and the cap rises. Fluid then enters the overflow tank until enough pressure is relieved to allow the spring to force the bottom seal back into place.

You'll also find on the bottom center of the cap that there's a brass or stainless circle plate. That circle plate actually creates a one way check valve. When the engine cools back down the coolant shrinks in volume. As that happens the pressure in the coolant system becomes a vacuum pulling down on the bottom circle plate and thus opens the check valve.

Once the valve opens the fluid is drawn in through the tube that leads to the bottom of the reservoir and refills the system. The system is actually self burping in that it evacuates air on each temperature cycle. Air is pumped out when the system gets hot and fluid is then drawn in when it cools.

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Hi Phil,

Well I think you and Smeggie have sort of covered it (and Smeggie's dead right about his rad cap operation info), but just to re-cap. In my opinion the only reason either of you get the sudden flow of water out of either the rad filler or the top hose is because on initial fill up the top of the head has been left in an air-lock due to the thermostat sealing too well.

 

As the engine warms up ( and probably starts to boil a little, locally - I hope this is just when idling in a garage rather than being driven) then the thermostat starts to open at long last due to the steam. Now the air can escape, more water enters a rather hot head and 'boom' you have a steam flash-off case and water gets pushed out in all directions.

 

The nasty bit about all of this is

1) the head gets too hot anyway, then

2) suddenly as the airlock shifts and water flows in you then you get sudden shock cooling.

If this is what's happening I'm sure its not healthy for the head or the head gasket...!

 

So I'd recommend either drilling the thermostat bleed hole, or remove the heater tap rubber hose on first start up to get that air out of the head and get it nice and full of coolant.

Hope this helps..

 

NTC - I've read quite a few of your posts, and while they do have good snippets of advice in I notice that most times they are only 1 or 2 sentences long at most. If the recipient isn't fully familiar with the topic I can often see why they can be left perplexed. Could I suggest you pad out your advice?? Please don't bite my head off, am only trying to be constructive....! :ph34r:

 

I'll happily accept that perhaps I can be too verbose... :rolleyes: !

 

Cheers all,

James.

Edited by jamesStag
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I had problems with trapped air a few years back

 

I drilled and taped a counter sunk screw in the top of the thermostat housing

 

This can be used to realize trapped air, comes out like a presure cooker

 

And can be checked easly

 

Pink

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Phil,

Having mulled this overnight, I've remembered another detail from when I had the problem (several months ago). I need to update my post from 6th July, as I now recall that when diagnosing this and I removed the heater hose from tap on top of the head initially although I'd filled the system at the rad, with the engine running there was no water flow from the top of the head at all, even with a few revs on.

 

So this is when I realised that the air-lock was sufficient that the water pump was not even priming. I stopped the car. removed and drilled the small bleed hole in the thermostat plate. On refill and re-try all then worked as it should straight away. water coming out of heater tap, etc.

I then slid the heater hose back on, kept topping up the rad as the engine warmed up. Then as normal thermostat opened and steady flow started in the top hose (i.e. no sudden rush of air/steam..)

 

Hope that's of use.

James.

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I am a bit late to this but here is my version.

 

It sounds initially like a simple air lock.

 

The simple solution is to fill the radiator and replace the cap then remove the heater hose from the back of the head and "back fill" until water comes out of the "tap". This means the heater is purged as is the head. Replace hose.

 

Having said that the system is designed to self purge that is why the radiator cap effectively has a 2 way flow, it will purge air and water into the overflow bottle then suck water back in when it cools. It sounds good but if you have a big air lock there is not enough water to take up the space when the initial air is purged, and here is the problem, with air in the system the system will not pressurize.

 

It is the pressure in the system which raised the boiling point of water, and thus allows the fan and radiator to efficiently cool the liquid and maintain a working engine temperature.

 

If the system is not pressurized enough then the engine will run hot/boil over as the cooling system will not be able to cope. This is why it is possible to boil over on a hot day when it has never happened before.

 

So that leads me to the rad cap, as has already been mentioned, forget 7psi go for 13psi, as this raises the boiling point and allows the cooling system to run efficiently in hot weather.

 

My recent experience of this was a car I was de bugging after a rebuild by others. The engine kept running hot and boiling over. I found 2 hoses to be weeping which prevents the system from pressurizing, I then discovered the cap which was brand new was a 7psi cap and missing its seal. I then removed the thermostat housing to find the thermostat was in backwards but what about this then, I had the presence of mind to check the working of the brand new thermostat only to find it was a duffer.

 

The moral is check everything and assume nothing.

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