GT6 Boiled Over...

[Kevin Atkins]

Afternoon all,

Oh dear, my GT6 experience has so far been one of maximum pain...

As part of restoration work, I have fitted a number of new parts to the cooling system -

• New water pump;
• New radiator (was leaking);
• New radiator cap;
• New thermostat (with poppet valve to allow air bleed);
• New heater matrix (also was leaking);
• New hoses;
• New bypass pipe (stainless steel, original was leaking);
• New heater control valve .

Since doing this, I have been through two top hoses, which have both split along the seam. I did notice that after running the engine for a short period to check for leaks, a few days later there was still excess pressure in the system when I removed the radiator cap. This seemed a bit odd - I would have expected pressure to have equalised to atmospheric pressure after cooling down fully.. I have, I believe, bled the system correctly but it's possible there is still an air lock; the other possibility I thought maybe the head gasket is blowing into the cooling system? But starting from cold with the radiator cap off, I'm not seeing any evidence of bubbling into the coolant, so it's a puzzle.

But for two hoses to let go, something is clearly wrong and there's excess pressure in there - still not sure why the rad cap didn't open and vent through that but there we are.

All ideas welcome - at this juncture and having spent more time under the car than driving it over the last six months, I'm getting close to the limit of what I can endure, both financially and the amount of time I've sunk into it..

[Steve P]

Have you tested the circulation around the engine/heater by taking a hose off to see if it comes out both ends?

S

Edited July 3, 2023 by Steve P

[johny]

hmmm not a good sign that there was residual pressure as I can only see one way that can happen and its when gas has been added to the system after it was filled. Normally on cooling it will return to the original state (atmospheric pressure) so I believe you have a head gasket leak that perhaps only shows itself when the engines hot and/or at higher revs. You could try retorquing the head...

[dannyb]

I had a head gasket fail recently.  Compression test ok. But when I pressurised one of the cylinders with a leakdown test I had bubbles  in radiator. 

Danny

[Kevin Atkins]

57 minutes ago, Steve P said:

Have you tested the circulation around the engine/heater by taking a hose off to see if it comes out both ends?

S

Good idea, I'll give that a try - is there a particular way to bleed the cooling system when filling from completely empty? On an old Rover Metro I had years ago, the heater hoses had bleed valves in them and it was a cinch to get the cooling system operating correctly (and also, none of the mythical K-Series head gasket issues ever encountered)

48 minutes ago, johny said:

hmmm not a good sign that there was residual pressure as I can only see one way that can happen and its when gas has been added to the system after it was filled. Normally on cooling it will return to the original state (atmospheric pressure) so I believe you have a head gasket leak that perhaps only shows itself when the engines hot and/or at higher revs. You could try retorquing the head...

Yeah I was wondering that, maybe only happening when hot.. Retorquing the head bolts sounds like a good plan too, nothing to lose anyway!

33 minutes ago, dannyb said:

I had a head gasket fail recently.  Compression test ok. But when I pressurised one of the cylinders with a leakdown test I had bubbles  in radiator. 

Danny

I did do a compression test a few months ago, albeit dry so not testing for leakdown, and the figures were all within a few percent of each other so the top-end seemed healthy enough then. I think I'll try another compression test too though.

Thanks for the replies gents, appreciate the help and moral support!

[Ian Foster]

Hi Kevin

The GT6 cooling system can be a bit of a challenge. It's marginal at best.

I am surprised that there is pressure in the system after a few days, as there should be negative pressure as the engine cools which draws expelled coolant from the overflow bottle.

My immediate guess would be that there is an issue with the radiator cap. Are you using a 7lb or 13lb cap? (not sure why it changed from mk1/2 to mk3). The radiator cap is sealed at two levels. The lower seal sits in the inner shelf and is responsible for regulating the pressure via the spring, allowing excess coolant to be diverted via the space between the lower and upper seal to the overflow bottle. The top seal in the cap closes off the whole system. There is a small brass valve on the underside of the lower seal which opens under negative pressure. For the return flow from the overflow bottle to the radiator to work, there needs to be a good seal around the top of the radiator neck (this was an issue for me). If you put some fine wet & dry on a flat block and tickle to top surface of the radiator neck, you will see whether you have any high/low points.

Secondly, are you sure you have fully bled the system. It's not easy to do and I have developed my own routine, which essentially uses a bleed bucket in the radiator neck and also a tapping in the thermostat housing, which is the highest point in the system. (I experimented with a header tank at one point which is why I have the tapping).

The heater control needs to be set to hot. I fill really slowly without the engine running and with the thermostat tapping open (small elbow, short pipe and small funnel attached), giving the two top hoses and the bottom hose a good squeeze every now and then. I then fit my bleed bucket (actually just a juice bottle) add a bit more coolant to create a small head and then start the engine and wait for air to start bleeding out of the radiator and thermostat. I add more coolant as required and massage the hoses. It's surprising how much air appears. If things start to run away as the engine gets hot (and it can with an unpressurised system), just turn off for a bit, let it cool and then repeat . When you get no more air out let things cool a bit, remove any excess coolant down to to the neck/thermostat housing level, fit the cap and close the bleed.

It's a faff but it works for me. Hope this helps!

Ian

 

Edited October 7, 2023 by Ian Foster
spelling

[Gully]

The Owner's Manual has the following to say about refilling the cooling system from empty:

1. Refit the bottom hose

2. Close the block drain tap

3. Move heater controls to 'Hot'

4. Fill the system through the radiator filler. Refit the pressure cap and half fill the expansion tank.

5. Run the engine at fast idle for 30s, stop the engine and top up the system through the radiator filler. Refit the pressure cap

6. Run the engine up to normal temperature. Stop the engine, allow to cool, then top up the expansion bottle to half full

I've always used this approach - seems to work for me. Only challenge I've encountered in the past is getting a radiator cap which seals sufficiently to pull the water back from the bottle as it cools - even when the seals are okay, some leak from the centre rivets and pull air instead.

Gully

[Kevin Atkins]

Thanks for the really detailed reply Ian, that's very helpful as I'm not sure I've got all the air out of the system - the real trouble has started after replacing the heater matrix, so whilst the system is now fully fluid tight (well, it was until the hose burst 😉 ), it's entirely possible I've not bled it properly, especially having read the care you've taken when doing the same.

The system is fitted with a 13 lb cap I think, bought from Paddocks if I remember correctly. I've also used an 82 degree stat, and the temperature gauge has always registered just above the 'quarter' mark on the dial in normal driving - it had hit past the half-way mark when I noticed steam pouring out from under the bonnet on my drive when it boiled over after a ~ 3 mile drive. Could I rig some sort of bleed valve into the thermostat housing to inlet manifold hose, to achieve the same thing as your tapping into the housing? Paddocks mention a radiator bleed hose too but I'm not sure where / what that is..

[Kevin Atkins]

12 minutes ago, Gully said:

The Owner's Manual has the following to say about refilling the cooling system from empty:

1. Refit the bottom hose

2. Close the block drain tap

3. Move heater controls to 'Hot'

4. Fill the system through the radiator filler. Refit the pressure cap and half fill the expansion tank.

5. Run the engine at fast idle for 30s, stop the engine and top up the system through the radiator filler. Refit the pressure cap

6. Run the engine up to normal temperature. Stop the engine, allow to cool, then top up the expansion bottle to half full

I've always used this approach - seems to work for me. Only challenge I've encountered in the past is getting a radiator cap which seals sufficiently to pull the water back from the bottle as it cools - even when the seals are okay, some leak from the centre rivets and pull air instead.

Gully

Thanks Gully - I think I did it this way but I might have filled too fast and trapped air in there.. I'm kind of hoping it is an air lock and not head gasket.. but gut feeling and other replies suggest it might be the HG.. but I'll get some compression tests done too, and try re-torquing the head

Edited July 3, 2023 by Kevin Atkins

[Kevin Atkins]

Just done a compression test, which seems to have yielded a conclusive result, I think - all cylinders except 5 are showing 145 - 150 psi, which agrees with the results from when I did a test about 6 months ago. Cylinder 5 is showing 125 psi... to me that looks like it's down a bit more than simple measurement error? Looks like I'll be taking the head off I guess..

Am I OK just buying a full gasket kit (Payen?) or is it recommended to get the studs / nuts too? I'd probably be buying from Rimmers or Paddocks as Canley Classics are away on holiday this week (and I've got this week off work)

 

[Iain T]

Inspect when you take the head off. A good set of hardened stud washers is essential. 

Iain 

PS   I had to change my rad cap as it didn't seal. 

 

[Ian Foster]

2 hours ago, Kevin Atkins said:

Paddocks mention a radiator bleed hose too but I'm not sure where / what that is.

Hi Kevin

I suspect that is the additional hose from the thermostat housing to the radiator neck. The GT6 is the only car in the range to have this, so I suspect Triumph were struggling from the get-go! 

Noted what you report re #5 cylinder reading, but please exhaust other possibilities before pulling the head off. Was your compression test carried out dry or wet and did you have the throttle fully open?

I still suspect a dodgy radiator cap and hope you might be able to try another known cap before going further.

Gully, I note what the WSM says, but in my experience it's not that easy and even modern cars have a more comprehensive bleed procedure. 

Ian

[Kevin Atkins]

1 hour ago, Iain T said:

Inspect when you take the head off. A good set of hardened stud washers is essential. 

Iain 

PS   I had to change my rad cap as it didn't seal. 

 

Thanks for the heads-up on that Iain.

1 hour ago, Ian Foster said:

Noted what you report re #5 cylinder reading, but please exhaust other possibilities before pulling the head off. Was your compression test carried out dry or wet and did you have the throttle fully open?

Thanks Ian, I did the test dry, but throttle was closed on all cylinders - not sure if I've got that wrong? I can re-test with throttle open if that's the correct way to do it. Also thinking of maybe try re-torquing the head as well, and run compression test again afterwards? Only thing that slightly worries me is if there has been a blow on the HG due to maybe slightly relaxed torque, the fire rings on the HG might have been damaged so any 'fix' by re-torquing might only be temporary? .. but I'd love to not have to take the head off if I can get away with it. Also noted re. the rad cap - I can try another one, and I'll check the mating face on the radiator too..

Edited July 3, 2023 by Kevin Atkins

[Iain T]

Compression test procedure is take out all the plugs (less work for the starter) and turn over with the throttle wide open. It gives a false value with the butterfly's closed. 

Iain 

[Iain T]

12 hours ago, Kevin Atkins said:

Thanks for the heads-up on that Iain.

If you use deformed or soft washers you can loose pressure and dare I say it cause the head gasket to fail. 

Iain 

[Stratton Jimmer]

Whenever I have refilled my systems from empty I have always half filled the system then started the engine with the radiator cap off. I then add coolant slowly and steadily. The heater is always set to hot. I have seen the rad apparently full but then bubbles appear and the level drops. Top up and go again. Once the thermometer is showing around 70 degrees, I stop the engine, fit the radiator cap and run it again until it is at full temp (circa 90 degrees in my GT6). I then let it cool down, remove the cap and top up once more which rarely takes more than about 20cc. Touch wood but I have never had any overheating issues. Note that myGT6 has both its original belt driven fan and an electrical driven fan in front of the rad. The electric fan is manually switched and is rarely used. My Sixfire has only a Kenlowe thermostatically controlled fan and is also free of any overheating. Both cars are using Evans waterless coolant.

[Iain T]

I've always refilled my Vitesse by raising the front to get the rad higher (drive it up ramps), opening the heater valve and filling. After a fill start the engine cap off and squeeze every hose I can then go for a spin, cool down and top up. 

Iain 

[Kevin Atkins]

Here's an update on today's progress.. With engine cold, I re-checked cylinder compressions, throttle wide open. Apart from cylinder 5, which measured 112 psi, the others were in the range of 130 - 140 psi.

I re-torqued the head nuts - not sure if I might have messed up, but here's what I did.. working in reverse sequence according to the Haynes manual, I slackened off all the nuts by half a turn. Doing this resulted in all the nuts ending up actually quite loose. I then re-torqued each to 44 ft lb in the sequence given in the manual, then reassembled everything, torquing the rocker shaft pedestals to the figure given in the Haynes manual (25 ft lb).

I then re-checked cylinder compressions - all now in the range of 105 psi to 117 psi (cylinder 5 was now actually the highest reading at 117 psi), so overall down somewhat on before.. Not too encouraged by this to be honest.. Maybe I should have slackened and re-torqued each nut one-by-one?

Anyway, I dressed the radiator cap flange per Ian's recommendation - there were some high spots where paint thickness varied, so I flatted to give a nice even ring of brass showing.

Carefully refilled system and ran engine up to temperature with the cap off. No evidence of bubbling into the coolant, even with the thermostat open, so kind of as before I think.

Just debating whether to risk a short test drive and then re-check cooling system once it's cooled down? The compression test results are a little worrying and concerned I might end up with the HG giving out completely and ending up with mayonnaise in the cooling system...

[Iain T]

Mmmm, I'd wait until the system is completely cool and see if you still have pressure in the coolant system. Also note the colour of the coolant. I would then do another compression test. It may be just an anomaly with your gauge. The testers are not necessarily accurate but helpful to show differences between cylinders. Does your gauge screw in or just push in to seal? 

Having said the above my worry beads would have me taking the head off! 

Iain 

[Kevin Atkins]

Hi Iain,

I didn't run the cooling system up to full pressure before, the cap was removed, although coolant colour is normal so I don't think there's been any cross-contamination. Just rechecked the compression on a couple of cylinders with the engine now tepid and they're the same as before. The compression tester is a cheap Chinese thing from Amazon but it's the screw-in variety. Mindful of it likely not being particularly accurate, but the changes in readings are what have caught my eye, both before / after head re-torque, and also the lower reading on cylinder 5 from when I tested a few months ago.

The only other thing I can think of is maybe I've disturbed the valve clearances and possibly valves are now not closing fully? But that'd have to be quite a shift in gasket compression I'd think to eliminate 10 thou?

I'm minded to pull the head - I've possibly made work for myself but it'll be an interesting exercise I guess.. I've done Minis before, so hoping this is similar, if a little bigger! I think as I've disturbed things, and maybe fouled up, I'm not confident of it holding up. This car hadn't run in over 10 years when I bought it, and there have been many issues so far, I haven't really had an opportunity to drive it regularly and get a proper 'feel' for when things are failing, which has made fault diagnosis difficult, beyond finding obvious problems like the external leaks, and I'm short on experience and knowledge, so it's been an interesting ride 😜 I really should have spent more on a better car at the outset, but that's hindsight..

[Iain T]

The Triumph six pot head is a bit heavier than a mini💪 As to experience there's plenty on the Forum who are happy to help. 

However as you have disturbed things do check the tappet clearances........you never know until you measure! 

Good luck and let us know how things progress. 

Iain 

 

[Iain T]

2 hours ago, Kevin Atkins said:

The only other thing I can think of is maybe I've disturbed the valve clearances and possibly valves are now not closing fully? But that'd have to be quite a shift in gasket compression I'd think to eliminate 10 thou?

Just a thought, did you have spacers under the rocker shaft pedestals? If you did have you put them back on? 

Iain 

[Kevin Atkins]

29 minutes ago, Iain T said:

Just a thought, did you have spacers under the rocker shaft pedestals? If you did have you put them back on? 

Thanks Iain, there were no spacers - I did take care to clean all oil from the mating faces so the pedestals went on and seated metal on metal so to speak.. when I removed the rocker assembly there were puddles of oil left on the pedestal mating faces.

I'll check the valve clearances in the morning, it'd be great if it's just a case of resetting clearances!

Cheers,

Kevin.

[Ian Foster]

Hi Kevin

You haven't stated whether your car is a Mk1, 2 or 3. From the use of a 13lb radiator cap I had assumed a Mk3.

If that is the case, the cylinder head uses the bigger 7/16" studs and should be torqued to 65-70lbft (the Mk1 has 3/8" studs as is torqued to 42-46 lbft)

You said you had re-torqued to 44lbft.......

Ian

Edited July 5, 2023 by Ian Foster
spelling

[johny]

Funny that as my workshop manual (free to download version from @vitessesteve) has 65-70 for mk2 GT6 and Vitesse but actually for mk3 GT6 it shows 60-80!