coolant being pushed out only under load

[mytmk3]

Right im pretty sure I already know where this is heading but you never know your luck in the big city someone may have some insight other than bhg...

motor

rebuilt/forged internals 7mgte done maybe 10-15,000kms
arp head studs cometic 2mm mhg
heater removed
cheap large alloy radiator
t70 turbo yada yada tuned to 515rwhp

The temp never goes above 92c it normaly sits around 87c and cruising can sometimes go as low as 79-80c readings are from my standalone ecu using the stock probe.

if I drive the car normaly even giving it quite a bit of stick on the flat its fine temp is fine and coolant level doesn't really change much in the overflow

If I drive it hard around the hills temp still stays perfectly fine water and air temps but check at the top of the hill and the overflow is full!

Oil is clean
take the cap off and run the car no bubbles
no steam from the exhaust or smoke it runs clean
no loss of power
plugs so no evidence of being washed

the scetchy side

-I havent re-torqued the head studs(they are not new though have been used 4 times)

-one of the hex plugs in the spark plug valley between no 3-4 weeps coolant (probly one of the main issues but has always done this for over a year yet coolant issues only started recently) cant tighten or remove it ive tried but it feels like its just going to strip and yes with the proper tool

-So in my grave frustration a mechanic suggested one of those copper additive shit and I tried it (it didnt help either lol)

My next steps I plan on doing is....

coolant flush and put in my stock radiatior see if there is a change
already changed the radiator cap did nothing.

What is the chances this all being from the copper bollocks as I dont recall any coolant issues before hand?

I just got a bottle of radiator flush and some new coolant I dont know weather to do one step at a time flush and still use my alloy rad or flush and put in my old stock radiator

 

[mytmk3]

also should add I used to run a 1.1bar radiator cap one that came with the radiator but that used to leak so its running a .9bar one at the moment

 

[Another MkIII]

So is it actually losing coolant, or is just being pushed into the overflow tank?
-AM3

 

[mytmk3]

just pushed out of the overflow coolant levels never change on regular driving just having fun around the hills but in my haste I dont see if it fully sucks it all back in overnight leave it for and hour or so and take of the cap hear pressure release and top part or radiator is low due to it all being in the overflow bottle.

when I syphon the coolant back levels are pretty much normal I know a little bit exited the resivoir when it was full.

Im not using the stock overflow either maybe mine is too small for how much it breaths when its getting beat on

 

[Nick M]

So you can pull the resevoir, unplug the sensor, and pour the coolant back in to the normal level?

 

[mytmk3]

So you can pull the resevoir, unplug the sensor, and pour the coolant back in to the normal level?

this is what I did today yes.

Last week when I first noticed it I was going alot harder (didnt think had any issues) for longer and also at the start of the day the overflow tank was filled to a higher level I lost coolant on the ground temps never rose though.

should the amout of coolant being displaced remain the same weather its spirited or regular driving? how many mls is it expected to rise?



Coolant loss only occurs from the exit hose from the overflow bottle if the bottle doesn't overflow the coolant doesn't need topping up.

I first thought that maybe the coolant wasn't returning to the rad when cold so it had eventualy filled and made a mess but after checking the levels this morning -normal

went for drive - slightly higher but I expect that when its warm but checked it twice in 30 mins while driving on flat no change

went up hill checked at the top overflow was full

drove it really easy home and was still full when I got home unfortunatly I opened the cap a few hours later and released the preassure do im unsure weather it would have sucked all the coolant back in by itself or not.

Im worried If I go for a harder longer drive it will keep pushing out more and more till im in trouble or if it was at its peak point of filling the container I really hope im making some sence :S

at the top of the hill looking in the overflow bottle I could see 1-2 bubbles come up to the surface

 

[Mikael_7m]

Maybe there's air in the cooling system? Have you had a chance to burp it.
I installed a larger aluminium radiator recently as well and i was thinking that maybe its overflowing a little more due to the increased water capacity.
I could be completely wrong though

 

[SideWinderGX]

When you take off the radiator cap is air rushing OUT or INTO the radiator?

 

[supraguy@aol]

It almost sounds normal.
If coolant is being pushed out by combustion gasses, that would mean you could test for the presence of those gases.
And IF you have a leaking HG, I'd say it might be solved by a retorque. Not that your bolts might have stretched, but your MLS HG might have compressed slightly.

 

[IndigoMKII]

It's staying normal under normal conditions because the CHT isn't climbing much but when you put it under a load the CHT's climb causing excessive coolant pressure. Sounds like you've got the very early signs of a BHG to me. I'd do as supraguy suggests and try to retorque.. Back off the nut first then torque it for an accurate torque.

 

[jonahs_supra]

my old 87 supra did this too
never burned or mixed coolant
but the coolant in overflow resevior would push out
actually burped cooling system multiple times and even put system on a vaccum
finally the headgasket blew lol

 

[mytmk3]

When you take off the radiator cap is air rushing OUT or INTO the radiator?

I opened it an hour after I drove it and air was going In I think

 

[IJ.]

If the overflow/recovery tank is too full this is normal and the system if leak free will find a level in a couple of days driving, the whole concept of the system is water gets hot and expands in the engine/radiator, this will bleed off some pressure/coolant to the tank, as the engine cools the coolant contracts forms a vaccum which sucks coolant from the tank back into the engine preventing any air in the system.

If there is a leak of any kind it can't do this as there's no vaccum.

 

[mytmk3]

well I re-torqued the head studs for peace of mind anyway as every time I see a thread about doing it I feel guilty that I havent.

my overflow bottle is pretty small so Ill run it at a real low level take it up the hills this sunday again as ive never managed to fill the bottle on the flat may do a coolant flush and change and burp before hand too and see how it all goes

now if the bottle fills again how long would it take to normalise/suck it back in? if I parked it up for 2 days should it be back to normal?

 

[mytmk3]

Here is my small overflow bottle

 

[radiod]

well I re-torqued the head studs for peace of mind anyway as every time I see a thread about doing it I feel guilty that I havent.

Unfortunately if that IS the issue, retorquing it now won't likely help :S

now if the bottle fills again how long would it take to normalise/suck it back in? if I parked it up for 2 days should it be back to normal?

When the engine is back down to ambient temperature it should have sucked all the fluid that was pushed out. If there is air in the system that was burped out while driving, the coolant level in the resevoir should be lower to replace the space that air was taking up.

 

[IJ.]

Does your overflow bottle have a sealed syphon tube to almost the bottom ot the tank?

 

[mytmk3]

Does your overflow bottle have a sealed syphon tube to almost the bottom ot the tank?

The black hose goes from the radiator to the tank and sits pretty much on the bottom always below the coolant level anyway

 

[IJ.]

From memory the 7M will push about 700 Ml around from stone cold to hot, my recovery can was only just big enough to cope (1 litre polished SS one)

The correct radiator cap plays a big part in this system as well.

 

[GrimJack]

Also, the siphon hose in the overflow tank must be pristine... if there is a hole in it, it'll suck air back in instead of coolant, and eventually your bottle will fill up. Think of trying to suck through a straw with a crack in the straw.