Boiling the coolant

[Colesy]

Changed the rad last weekend after the last one cracked, everything seemed fine until I took it on a long run to Glastonbury this weekend just gone.

On the way down I arrived at destination checked the coolant and saw that there was a small leak from the small top hose of the rad, so I tightned the jubilee, topped up the coolant and assumed it would be ok.

Kept checking it over the next few days on short runs and it was fine.

Then on the long run back after about about 3 hours driving and having checked the coolant within an hour the temperature started rising up to about 3/4 of the way from 90C to the first of the two dots, then the coolant light came on - thankfully just before the services I was planning on stopping at. Opened the bonnet and the expansion tank was almost empty and there was steam coming from the cap. So I let it cool down for a while and filled up the coolant tank with water (didn't have any coolant fluid) - it took about 5 litres which was a bit of a worry as it must have lost almost all of the coolant very quickly.

Then after this I kept a very close eye on the temperature which seemed stable at first and then gradually started to climb. So in the burning heat of yesterday I put the heating on full which was horrible but very affective at keeping the temperature down. This was ok on the M3 with the windows open but in London traffic it was too much so every so often I turned the heating off. But, after 5 mins or so each time had to put the heating back on to reduce the temperature as it was rising rapidly. Got home eventually half baked but in time for the football!

So I'm quite concerned now!

As background there has been an intermittient issue of mayo on the dipstick which comes and goes and has been put down to condensation, never any on the oil cap. The compression on all cylinders is good and it never uses any water. It uses very little oil, there are no bubbles in the coolant and the coolant has been tested for gasses and was ok. Before the rad blew the temperature used to sit about 1/4 of the way between 90C and the dot. I did notice straight after changing the rad that the fan seemed to be working harder and seems to have changed its tone, although this could be because the undertray isn't back on yet.

I'm running without the aux rad btw so my initial (simplistic) reaction is to blame this and the extreme weater conditions or is this as I fear a more serious head gasket issue?

Sorry for the essay but hopefully with the whole story a diagnosis can be found.

Thanks in advance.

[panzerwagen]

This has happened to me...

Just by coincidence when you replaced the radiator, how did you remove the cooling fan? If you were not careful, I would bet you broke the connector or it was finished and you replacing the radiator just gave it a push to it's end. Sure way to know is turn the key in your ignition & turn on the AC at it's lowest setting. If the fan does not kick in at high speed you will know what has happened. Is the fan (-) grounded correctly? Have you checked the fan wiring for burn marks or scortching at the plug? Another thought.....Are you sure there is no air bubble in the system.
Did you bleed the system correctly?

[Knight Rider S4]

As above

Did you bleed the system ok
How is the Aux rad blocked off?

[Colesy]

I'll check the fan for scorches etc when I get home tonight, I was quite careful when I removed it though, which connector are you referring to which I might have broken?

I've bled the system each time I've added water and it seems to have worked fine afterward with a constant stream of water into the tank and no bubbles from the rad bleed screw. I'll also try to eliminate the air lock possibility tonight as well.

The Aux rad it blocked off using a bung in each pipe.

One of the strangest things I noticed yesterday was that when cruising at 70ish when the rad should be at it's most efficient it still got hot...

Thanks for the ideas!

[Rusty]

These old buses are hard to bleed properly. You need to get take the expansion tank off it's mounting points and lift it up as high as you can when bleeding the top of the rad, this will help. Then get it up to temperature and let the fan cut in a few times, it should self bleed then with the thermostat open. When all cold (leave it overnight), again, lift up the expansion tank and bleed the rad, then top up to the minimum mark, at running temp it should be at max.

I've had problems with this after playing with the coolant and it's down to patience and skill I'm afraid, might have to bleed it a few times before it's all sorted and works properly. Had it way up once after not bleeding it properly and also had it way up on track - this was a weak headgasket.

I'm not running the auyx. rad either and it's not an issue in the mild temperatures we get here, I have hardwired the fan for sitting in traffic in 25+degC tho

Leave the car running with some card underneath, that'll highlight any problems with the oil or water...

Good luck with it, at least you were able to catch it.

[Ruffiano]

just had a similar set of issues, Now i'm replacing a head gasket.

[Jamo]

just had a similar set of issues, Now i'm replacing a head gasket.

[SamH]

To bleed the radiator can you not run the engine and build up the pressure then release the cap on the overfill tank and let the bubbles come through the system?

[panzerwagen]

Bleeding coolant...

Sam there are several ways to do it but the way I have found to work everytime all the time is this...
Run the engine until all hoses are hot, crack open the coolant bottle & leave cap off, them take the small bleed screw out of the hose going to your heater core. If you can take the bleed screw off the top of the radiator(Seldom can this be done but you can always try). With the engine running, blip the throttle cable a couple of times to force the coolant to move quicker through the system and to move any air bubbles out the nearest access port. When you see coolant coming out of the heater hose when you blip the throttle, put the screw back in.

[DamianURS4]

reminds me of when my head gasket went....

[SamH]

Bleeding coolant...
Sam there are several ways to do it but the way I have found to work everytime all the time is this...
Run the engine until all hoses are hot, crack open the coolant bottle & leave cap off, them take the small bleed screw out of the hose going to your heater core. If you can take the bleed screw off the top of the radiator(Seldom can this be done but you can always try). With the engine running, blip the throttle cable a couple of times to force the coolant to move quicker through the system and to move any air bubbles out the nearest access port. When you see coolant coming out of the heater hose when you blip the throttle, put the screw back in.

Thanks for the advice, I think I still have a little air in there so I will try this method, but where is this hose? I have the replacment samco one left over from when I changed the cooling hoses over as I couldn't see where to get at it.

[Colesy]

Had a chance to properly bleed the system this weekend as per everyones advice. Thanks!

I then took it on a drive across London to pick up my new suspension. Each way was about a 45 min drive in traffic and the temperature seemed to peak at about 2/3 of the way from 90 to the first dot, I checked the coolant at each end end and the level hasn't dropped and there were no leaks.

But I haven't had a chance to get it up to any speed though yet. Someone suggested to me that there could be a problem with the thermostat or the water pump for the car to overheat at 80. Is there an easy way to test either of these?

Am I right to be concerned at the overheating happening at speed?

Is the temperature that I'm getting up to a cause for concern?

[Jamo]

If your very very unlucky it could be that the headgasket has gone on the EM side so only when hot and on boost you get the coolant system pressurised but normal pottering around you get nothing.

[Rusty]

Weak thermostat will lead to cool runnings (mon ). If the water temperature exceeds 90+2 in normal fast driving then I'm afraid I'll have to plumb for the head gasket

[Fat Audi 80]

If going fast I would expect the coolant to cool again due to the increased airflow over the rad(s). If it is getting hot on a run that is bad sign....