Coolant Bleeding 1994 2.4 Petrol

[sleemanj]

Kiaora, my mum has a 1994 2.4 petrol Largo which is causing her some cooling problems and I stupidly said I'd take a look.

I've read here a technique to bleeding the coolant system on these, but having some trouble convincing myself I'm looking at the right "capped pipe" referenced.... picture tells a thousand words, so on the attached image am I looking at the right cap I should remove to bleed air from the system?

[the shiney one]

hi and welcome to the forum

[gixxerboy]

thats the pipe to bleed the diesels so would imagine its the same for the petrol model

[tommy]

Replace the cap on side of the engine

[tommy]

the bleed nipples are on the passenger side pipe with rubber cap under the seat, on the rear heater between the pipes, front heater between the pipes and the fill point is in you picture. replace the cap on the engine as this is usually why the petrol overheat. at a guess the temp guage randomly goes to 3/4 and goes back down when you drive?

[sleemanj]

A hidden second coolant cap! This is without a doubt the most complicated cooling (or perhaps heating) system I've come across, reading the threads here seems like air locks are a common problem.

The main issue, is blowing coolant back into the expansion tank, and boiling in the expansion tank (radiator not that hot, fans not running). I think I'll pull the thermostat tomorrow, replace both radiator cap and the second cap if I can find it, and try bleeding it properly.

Thanks all.

[tommy]

The second cap is your problem as that is the one that release's the water into the tank. The valve near the spare wheel bypasses the thermostat and the hose that usually splits is the one under the engine cap that goes to the head. When you fill it make sure it don't fill the tank as you fill it and if so you're cap is leaking.

[sleemanj]

Ah I was just going to ask about that mysterious valve. Should it be open, or closed normally (I'm guessing closed, to close the bypass?)

Anyhoo, I dismantled the beast and you guys were dead on with that cap, soon as I lifted off the tunnel it was obvious that it had failed to the point where coolant had obviously been ejecting itself from the system there. Taking the cap off, the rubber was perished, what was left of it. So replaced both caps.

I bled the system, I was unable to get anything out of the passenger side nipple though, sticking a thin diameter wire in got a few drops of BLACK water to come through, but couldn't find anything long enough to get very far up the pipe. Didn't bother with pulling out the thermostat, if this fixes it no sense climbing around on my back trying to get that out for a look (and if that valve totally bypasses it, that would be a good test).

Fired it up, idled for about 20 minutes and temperatures seemed ok, then it shot up hot and a bit of bubbling into the expansion, I shut it down and let it cool then gave it another go, idled about 25 minutes or so without issue, temperature planted in the middle. Perhaps that excursion to the hot zone was just a bit of trapped air escaping once the pressure was high enough and it was insulating the thermo switch closed. Expansion is cold, no bubbling, and eyeballing the level looks about the same.

I'll let it cool down and check the top filler pipe then I guess road test. May well still have a head/gasket problem after all this, but might be making some progress at least.

[tommy]

you will find that the radiator level drops to just above the fins when the level is correct under the rad cap. Also did you set the heaters to Full Hot by holding down the red button for the front and rear heaters? If you didn't bleed from the passenger side you would still have an airlock in the thermostat/block where the cap goes on.

[sleemanj]

Well I set the heater to full hot (and it worked), but I have no idea how to set the "rear heater", is it separately controlled somehow?

Seems to have a bit of a fuel or ignition issue now so wasn't able to give it a proper test run but what I did do seemed OK (two footed driving to keep the revs up and not die out on me), hoping that it's not related and just a blocked up filter from being run at E minus minus on the petrol gauge most it's life.