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k series overheat


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Hi recently changed my hoses to silicone re filled listening to all the little tricks to not get air locks. when i started it first time let it idle bottom hose got hot thought great job done then left it. couple of days later tried to take it out overheated so brought it back massaged hoses and it seamed to stabilize so gave it another run temp stayed around 70. Took it out today everything ok over a few bumps and swaying the car side to side just to make sure temp stayed around 70 so started to push it a bit more back to overheating brought it back to garage and it stabilized again my mechanic said i should drive it to get rid of air has anybody got any tips. i didnt do any mods to system its a dry sump r 300 no heater.



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The thing that made the biggest difference to me was drilling the thermostat flange.

Before that I could not get the airlocks out for the life of me. Since then, nothing to it.

2mm hole in the metal flange (NOT the plastic housing!) of the thermostat such that it is at the TOP when installed. Without it, any air in the system finds its way to the thermostat housing and can't get past the stat as with air insulating the stat it is reluctant to open. Result - stat stays closed and it overheats. With the hole, air escapes while filling and if any migrates to the stat housing while driving. Keeping the hole small stops it prolonging warm up times excessively.

As a side effect, the hole allows a little flow through the radiator when the stat is closed which prevents the water in the radiator from overcooling and stops the temperature cycling you get with the inrush of cold water as the stat opens, which is really not good for a K Series. Since drilling mine, temperature just sits at 85C whatever. Never moves, completely stable (with no other cooling circuit modifications).

I think Ian (SM25T above) may have a nice example picture of a drilled stat for you ...

PS: And yes do what SM25T says, then fill slowly from the bleed tee.

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Hi Gav, as someone who encouraged you to go with your silicone hoses, just thought I would continue the positive vibes. My K doesn't run a heater, but I did install a PRRT, and I subsequently knocked the guts out of the standard thermostat, which is probably why I've never suffered with air locks whenever I've disturbed the cooling system. Definitely drill your thermostat and try again from there

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I wonder why this T-bleeding part is not something standard on all the K-engines.

Before fitting that one which can be seen on the photograph, I had also battled with an erratic water temperature (the fighting was also due to an expansion bottle cap which was not perfectly tight - water level raising excessively in the bottle and eventually coming out).

With the T-bleeder at the highest point of the water circuit, the filling is extremely easy and the bleeding  doesn't require any special awkward operation.

For those who don't know, this is the procedure which I have used and which has given me total satisfaction (water temperature rising very quickly and stabilizing at 82-83 °C - and this for the last 1300 miles without touching the coolant circuit) :

Remove the expansion bottle cap and the radiator upper bleeding screw

Fill via the T-bleeding piece : water flows gently in both loops (the by-pass loop - including the heater for those who own one - and the radiator loop)

The water fills progressively all the cavities in the engine and the pipes.

As the level goes up, water starts to appear in the expansion bottle and as it reaches somewhere between the minimum and maximum, it also normally starts to flow out of the radiator through the bleeding port left open (screwing a small plastic pipe in this place allows to make sure that the level of water gets a bit higher and that the radiator is completely full)

It is the time to close the expansion bottle with a (perfectly tight) cap and quickly put the radiator bleeding screw in place.

Then one has just to complete the filling of the by-pass loop, eventually pulling the T-bleeding part upwards, so that the final level of water is above the highest point of the heater and makes sure that no air is trapped.

When the T-bleeding part is full, just put the cap on it.

Hoping to have been helpful to some of you, I wish you all a happy new year.



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Yes that's the way I do it too, and it works every time. No need for jacking or furious massaging. I have drilled the thermostat as described above too which helps a lot; I think filling it slowly helps air escape as well. Mine also warms up rapidly and then sites around 82-83 °C ver reliably, whatever the conditions. Again, no other coolant circuit modifications needed.


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  • 3 weeks later...

Hi Jonathan its not happening at the moment it seams to be ok and then it over heats again went to take it out for a short drive today and forgot my wallet so nipped back by the time i had nipped in the garage for the wallet it was overheating. So jacked it up high front end and massaged pipes again nothing but stat opened stayed steady. Took it out round the block brought it back stopped overheated again tried the jacking up a couple of times more but still the same. Looks like the air is around the stat so sometimes it works and sometimes not. So was thinking of drilling the stat but when refilling was going to take the bypass hose of the rail and making a temporary tee piece with a temporary hose to the rail and slowly fill once full taking the temporary bits off keeping my thumbs on hose and rail then pushing it back on quickly really dont want a full time tee piece unless i have to. what do you think im at my wits end with it 


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When you say "overheating" is it showing hot on the gauge and overflowing into the expansion tank?

I'd take the bit between my teeth and drill a hole through the thermostat. Have you got enough on how to do this? I'd also check the opening of the thermostat in a pan with a thermometer while it's out.


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Drilling the thermostat made all the difference to me.

The first time I had to refill the coolant I had similar problems to what you are experiencing now. Try as I might I couldn't get the air bled out and the system cooling reliably. In the end I took people's advice and drilled the thermostat. I now follow the procedure I outlined earlier. Never has a problem since.

Honestly, now I just fill it up and go and it is fine every time. My engine seems to go in and out more often than a cuckoo clock so the method has had a few trials! I've also used on friends' cars with the same results. There is no no need to jack anything up or massage anything. With the car on a flat level surface just fill it very slowly from the bleed tee in the order I described.

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Its showing hot on the gauge think ive turned it off before its got to the stage of boiling out of the expansion tank. I roughly no how to drill it, was just going to get a new one anyway as they are not expensive. My concern is does the whole thermostat housing have to come of or can i split it in position ? Ive got roller barrels and it makes hard to access it i struggled to get the new bypass hose on nearly dislocating my thumb lol. Also if i have to remove the full housing it will need a new o ring which i could order ready. When you split the housing does the thermostat have a rubber seal on it or is it another o ring i will need to get ?

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