Possible 7M BHG... opinions please

[whatthe?]

Hi all,

Yes, it may have happened, I may have become the latest victim of the dreaded 7M-BHG. I've done a bit of research and my symptoms sort of fit the profile but also may be something else. At this stage I'm just after some ideas to confirm/ deny the HG problem and some advice on solutions should it prove not to be the worse case scenario.

First, the symptoms;

Whilst driving reasonably hard on the putty rd on Sunday (regular boosting @ 12psi for about an hour or so) my temp gauge started to rise. We pulled over quickly (it never got over 3 bars above half on MA61 temp gauge which is 2 bars below max) and discovered that a fair bit of water/coolant was in the resevoir and infact some had been forced out of the drain pipe and was currently residing all over the chassis rail. We waited for it to cool down, cracked the cap off and added some water (didnt need a great deal). Took it a bit easier for the next few hours, no real dramas. Temp stayed at half or half + 1. All was good til we headed home down the F3 later on that arvo. At a constant 130km @ 3800rpm temp started to rise again. Slowed down and it behaved more or less til I got home.

Rang Joorsh for a little advice (he owned this engine before me) as I found a few posts by him on the old forums in regards to similar issues. He advised me that he had a similar problem with coolant not wanting to stay in it's rightful place after spirited driving which was fixed by a proper cooling system bleed (ie parked nose up on a hill, run for 15 mins or so til bubbles gone and bled out of the pipe attached to the heater solenoid on the firewall) and a 16psi rad cap to replace the factory 13psi job. I did both of these things and whilst the coolant seems to be staying where it should I now have another weird problem.

After heating the car up to running temp the temp guage now fluctuates between half and 2 bars from max temperature very rapidly (like 10 secs it goes to the top then back down to half again. Stays there for maybe half a minute then does it agin, it's like clockwork every half a minute or so). It doesnt seem to get overly hot though, after driving around like this for 10 mins or so I was still able to open the radiator cap with no more than a small his of escaping pressure and all coolant was where it should have been. It also doesnt matter how I drive, I can cruise off boost at 60km/h or I can stick the boot into it, same effect either way. Could this new higher pressure rad cap be showing up a dodgy thermostat or is this the dreaded BHG? I have none of the other symptoms I've researched, no white smoke on startup or whilst running, no water in the oil or vice versa, no continuous bubbling from the radiator, no noticeable difference in performance or idle. Just this weird fluctuating temp gauge thing.

Thoughts anyone? It isnt a dirty cooling system as I had my radiator recored with an adrad 3 core only a month or so ago.

[ed]

the wandering temp gauge = air in the system

why your overheating in the first place though?? do a systems fluch and check for starters, then when done right, start looking for water loss

[SL666]

Get a 2L coke bottle cut the bottom off and stick the neck into the filler of the rad, fill it 2/3 with water start the car and run until it warms up etc, make sure the heater tap is open...

could be a thermostat mucking around.. do you notice pressure in the rad system long after its cooled? what about any missing or farting when you first start it?

[Yian]

I'm with Ed. Shouldn't be overheating in the first place. Spirited driving in my car would only ever get me to half way temperature. 130km/hish on the freeway usually tends to yield 1 bar below half.

[whatthe?]

Well, gave it a good cleanout and ran it for 20 mins with the cap off after filling with 30/70 red coolant/water mix, burped it, bled the back hose etc etc. The temp gauge now sits on half way (as it always has since I fitted this new radiator) and after a bit of boosting will flit to 1 bar above half briefly before returning to half. On a cooler day it may stay on halfway. but then again it is 37 here today! Is this temperature level safe/ acceptable for this engine?

Edit: Will a higher psi cap make it run hotter? I'm just remembering from yr 8 science (oh, so many years ago) that pressure reduces the heat needed to boil water. The coolant seems to be staying in the radiator and the resevoir only has the water in it that I put there this morning (ie. just below half way). Might it be worth going back to my 13psi cap?

[SL666]

lower pressure = lower boiling point.. of course if it gets to that point it will push the fluid out into the resivoir..

[Norbie]

My Supra behaves in a similar fashion - sites on the halfway mark all the time, but after a bit of boosting it will creep up a bar or two and then come back down when I back off. Stupid MA61 front end makes it hard to build an effective cooling system.

As for the radiator cap, higher pressure doesn't change the temperature of anything, it just raises the boiling point of the coolant. This is good insurance if your car runs hot all the time, because as soon as you get boiling things go downhill fast.

[whatthe?]

Ok thanks for the advice guys, I can see why it runs a bit hot (filthy big FMIC, condensor and condensor fan/bracket assy in front of the poor old rad). The problem seems to be at least improved, I'll take it for a run up the freeway this arvo and see how she behaves. Think I'll leave the 16psi cap on, maybe some thermos could be in it's immediate future.... Just glad it doesn't seem to be that $^%$*&* HG.....yet.......

[SL666]

if its got a mechanical fan, taking that off and putting thermos on will most likely make it worse...

[The Witzl]

just do the head studs pre-emptively

[rvrolla]

I've read mixed reports about adjusting the head bolts/studs with out taking the head off and replacing the HG?

What HG has it got, MHG or standard?

[whatthe?]

I know for a fact that the studs are aftermarket and have been torqued down to 72lb +. The previous owner believes it has a MHG but cant be 100% sure. He bought it in a car which was a bit of a legend in it's day apparently

EDIT: Here's a quote from the previous owner posted on the old forums

joorsh wrote on Sat, 17 July 2004 02:07]Well for anyone that cares I just thought I'd post a little more progress on my baby. For those unfamiliar it's an MA61 with a 7MGTE in it. Had it inspected on the dyno the other day, and found it was leaning out a fair bit (13.1 at one stage). A few tests later and we found the fuel pressure was down by about 10 psi. Well, time for a new fuel pump!

In goes the little walbro 700HP number.

A few more tests, and now the fuel pressure is about 30 psi too high! Tracked the high psi problem down to the stock fuel flow regulator. Poor little thing just wasn't up to the task of 255 litres/hour - was proving to be a bit of a restriction, hence the fuel pressure increase.

In goes the adjustable fuel flow regulator.

Now all seems peachy at 38psi fuel pressure. Back on the dyno, and the afr's are sitting pretty on 11.5. A little richer than I'd like it, but much closer to what Mr Toyota ordered from the factory.

Now the head has been off my 7M, I know that much. As for what black magic was been waved under there I do not know - except that there's a non-standard gasget in there, different head bolts, and probably some kind of port work. The sort of things you want to do to 7M's.

Anyway, half an hour or so of tuning later and I've cracked the 600Nm mark, and I'm happy enough to leave it at that (it was a bit over 5500N tractive effort for all you purists). Wasn't really going for peak power, but all the same busted well over the 180rwkw mark - good enough for me, especially considering I limited myself to 9psi.

As they say, power wins dyno trophies, torque wins races.

The brakes have also been fixed up a treat. In fact now I find myself chewing on the steering wheel as soon as my brain registers the thought "brake". Took a little getting used to, but loving it now.

Well, enough babbling about baby.

-J-

[BlackSupra]

And i would only use genuine toyota coolant and would look at the mix ratio of that. Pretty sure its 50:50 isnt it?

I cant be arsed looking at a bottle to confirm, but im sure someone else can.

And if its a standard MA61 radiator it will struggle for sure with those temps.

You want the temp gauge sitting dead in the middle.

[rvrolla]

Yes 50:50.

[whatthe?]

I'm using the Nulon concentrate red coolant and it isn't a standard MA61 radiator, it has a ADRAD triple core with the standard top and bottom tanks, less than one month old. Is the toyota red stuff better?