Low pressure in cooling system (7mgte)

[kemicalx]

I'm getting a little paranoid as my 7m is exhibiting some BHG'esque symptoms though it's not showing others, anyway... after draining my coolant, jacking the front of my car while running and with the heater on refilled and burped the system. But afterwards found I still got the water rushing noise behind the dash when revving it, occasional bubble blowing from the overflow, which once overflowed when i spiked the boost over 15psi on a hot day just after the car had been left heat soaking and the coolant temp was sitting at about 90. But coolant temp generally stays below 75 only rising to about 77-80 once the car has been turned off, the coolant colour is fine, and when draining the old coolant it looked as green as the day i put it in. Oil colour is fine though getting a bit darker. But the pressure in my top radiator pipe is a fair bit lower than my mates, it still has pressure, but doesn't get really firm.

My block has been O-ringed and has a copper head gasket, but it's using the standard head studs and i *think* standard torque setting too. Though i have been led to believe i shouldn't really need a higher torque setting when using O-rings(confirm/deny) So i don't think my combustion chambers will ever take on water, but theres still the chance of water and oil mixing if the head lifts a smidge during boost.


Anyway, do any of you lads have an idea on what could be happening? I defiantly want to nab a potential BHG pre-catastrophic meltdown.

[Ribfeast]

75 is pretty low, what thermostat are you running?
I had a really small hole in my radiator that caused low pressure in mine, and temps would climb to around 95 up hills sometimes. New radiator and it sits on 85 avg, 90 tops.
Definitely need a higher torque setting than stock, as the stock setting was the cause of the original BHG.

I think there is stuff they can put in your coolant that changes color if there is oil or combustion gases getting in there.

[kemicalx]

i understand that the 54(?)ft/lbs was too low for a normal headgasket, but when the block is o-ringed the increased pressure around the cylinders from the wire squishing the copper acting like an extra strong fire ring in a regular headgaskets reduced the need for a high torque setting on the head bolts, i was under the impression you lowered the amount of torque on a head with o-ringing and copper?

My thermostat is a lower than spec one.. i can't remember the exact figure but it was consistant with the coolant tempreture of the car.

I guess a TK test will show all... if it's gone BHG, i guess i'll have to find out if i can just leave the head on the car and replace the bolts with studs then clamp it down some more.

[PHOBIA]

If it's a copper gasket, you won’t have a blown head gasket (BHG) but if you are running the head bolts at the factory torque specks than o-ringed or not you may be pushing combustion air into the cooling system past the gasket on boost. If you don’t have a receiver groove in your head than you will more than likely be pushing past the head/gasket side not the block/gasket side. None of this explains the low pressure of your cooling system though as systems of a lifting head will only be existent under boost. That said, you are not really running a great deal of boost, not enough to be worrying about head lift. Have you done a compression check on your cooling system yet?

[kemicalx]

I don't know if it has receiver grooves in the head, and to be honest i wouldn't think it would need them? i thought the idea behind o-ringing was to have grooves cut in the block, wire layed in them, copper over the top, the head just squishes everything down. and like i said, the temperature of the coolant suggests it isn't leaking combustion gases. but the gurgling behind the dash is damn loud..

i'm going to get a TK test done, and i'll get the cooling system compression tested as well

[PHOBIA]

For the boost you are running, no you probably don't need the receiver grooves. Get the pressure test done and see what results come from that. In general, I don’t think you have a HG issue though.

[kemicalx]

cheers mate, I have a feeling there's something dodgy in my cooling system. though if there was a small leak i would have thought it would have thought the symptoms would be more noticeable.

Biggest problem i've found with copper/o-ringing is the fact that not many people do it, and there isn't a heap of information available on the net to do with the process.

[PHOBIA]

Yeah, the copper gaskets are a little harder to reliably seal, but for high boost, they are the only choice really.

[kemicalx]

TK test confirms BHG... yay!

so now first thing i'm thinking I should do is, loosen my head bolts and then retorque them to the higher setting? then re-TK it? What do you guys think? keeping in mind this isn't a composite gasket.

[PHOBIA]

Are they standard bolts?? You could just try to re-torque them, don’t loosen them just re-torque them to a higher setting. I would look at possibly going for ARP studs or even a fresh set of standard bolts if you’re going to exceed the manufactures recommended specs by too much.

[kemicalx]

I'll definatly get a set of ARPs in the future, but just to see if the problem can be fixed without lifting the head, do you think re-tourqing the headbolts will work, and even if it doesn't do you know of any negative side effects of doing it?

[PHOBIA]

It has worked for me before, but mine was lifting the head at 22psi. I would let the motor cool for 4-5 hours and re-torque to 100ft pounds with ARP studs. Yours sounds like there is something else going on. For what it's worth, 10ft ponds over the factory specs won’t hurt it. Use the correct sequence and don’t over do it. It’s worth the 10min to try.

[Cruiser97_80]

Maybe you didn't quite get all the air out of the system to start with. My brothers 7m was an absolute biach. Ended up using a funnel in the top of the radiator and filling that right up.Let it idle till it got up to temp it gurgled away for ages. He was certain he had joined the BHG Brigade. But has been absolutely fine now for 6 months.

[kemicalx]

whats the deal with this,

when the car has just been turned off there is no gurgling present at the overflow.. but leave it for a couple fo minutes and when the engine temp has rised then it will start gurgling away... now i know in this instance theres no chance combustion gases are the cause

[Cruiser97_80]

I reckon you have a small air lock in cooling system / or a small leak.
I had a small leak on mr2, sounded sort of like the coolant was boiling but it wasn't.