I have been running my NG to and from work for the past week or so. Running to work in the cool moring air is fine. Running home, the weather has been warmer, and the temperature gauge shows a small increment, but the temperature holds steady. Could Any one please explain, why, on ariving home, I turn the engine off, and a few seconds later cooling water erupts from the filler cap all over the exhaust manifold, creating a impressive cloud of steam? It doesn't seem to have done much harm so far, but I am getting tired of refilling the system every day. BTW, the engine is Rover 2.6 Straight 6.

Hi Ian,
It sounds like you are overheating so,are the top and bottom hoses hot.
Do you have an electric cooling fan, and if so do you here it cut in, if not take the wires from your switch and join them together, this should make the fan run. You may need the ignition switched on to do this.
Then have you bled the cooling system to ensure all the air is out of it, and not trapped in the heater. You will need the heater set on hot to do this sucessfully.
Try these first before looking at more sinister things like thermostat or head gasket failure.
HTH
Mark

Hi Mark,

I spent a pleasent half hour on the side of the A32 a couple of weeks ago, with the AA man, geting the air out of the system after almost seizing the engine, and yes we did having the heater on, although it has always seemed pretty pathetic to me.

I am pretty sure that the fan is working, although I will pay more attention tomorrow.

I wonder if I might have a part blocked pipe somewhere. I know that one of the heater pipes was definitely blocked when I got the car, and I had to clean it out.

Cheers,

Ian

Ian, when you overheated on the A32 a few weeks ago, what did the temp gauge read?

Basically, I'm asking if it could be faulty and your car IS repeatedly overheating despite the gauge suggesting you aren't...

When I overheated on the A32, it was reading overheating, I was trying to nurse the thing home.

Actually I have an idea.

I noticed that the car generally boils over on my drive, and assumed this was because I had just driven home in the evenings heat, as apposed to the cool morning. Actually, I am coming to the conclusion that the problem may be because my drive is sloping downhill to the garage. This puts the radiator lower than the engine. and the expansion bottle fills up. Then, when the engine stops, there is no space for expansion and the valve blows hot water over the exhaust manifold.

I guess answers may be to move the bottle, fit a bigger bottle, or just to leave the engine running on the drive before putting the car in the garage.

I have also spent a fiver (second mortgage time) on a new filler cap incase the pressure spring is weakening a bit.

Perhaps, overheating on the A32 may have neen due to water seeping through the filler over time without me noticing until the level got just too low.

Dare I suggest that onto your drive should test that theory?!

Argh! The word 'reversing' is missing from above because I put it inside triangular brackets!

"...suggest that reversing onto your drive..."

Pah!

I have now fitted a new thermostat. The valve disc on the old one seemed to be slightly bent over, which might have prevented it from making a proper seal. I also noticed that the filler on top of the thermostat housing was blocked with scale. Clearing this made it easier to fill the engine with water. On filling I discovered that the expansion bottle overflowed, which does suggest to me that it is mounted too low down.

I ran the engine up to temperature in the garage and it seemed fine. I have a couple of other small jobs to do before taking it for a trial run, but it looks like I might need to make up a new bracket for the bottle.

Hands up, I don't know your setup but have a little experience with water systems.
Are you using a thermostat?
Is there a pressure cap on your radiator or just the "expansion bottle"

I don't know about the Thermostat. Will look.

The expansion bottle has a pressure cap, which I have replaced.

I have discovered that what is happening is that the water is boiling over when I park the car facing downhill since the water bottle is lower than the water level in the engine. I will remember not to stop the engine on a steep downhill in future.

Hi Ian, how many pipes communicate with your tank?
I have some thoughts that really need a two way conversation to expand. If you send me a landline number to my e mail address I will go through it with you.
Regards Mel.

But there is no logical reason for it to boil over when parked downhill other than there being some sort of air block which when the angle of the engine changes then moves allowing water to touch very very hot surfaces then boiling.
Simpy parking on a slope want change anything.
So is it'boiling over' i.e actively boiling or is it just running out?

If it is activeley boing then I would suggest you need to make sure all air blocks are out. A lot of people with Cobra replicas have airblock problems.

I have definitely, as an ignorant newbie, had some air block problems, but I am more aware of them now. I am not entirely sure of the best way to get rid of air blocks though, other than applying water and waiting for the air to bubble through. Squeezing the pipe at the head of the rad seems to help, as does unbolting the expansion bottle and waving it around like some sort of a drip.

It does strike me that the radiator seems to be quite small for a big, 2ltr plus engine. How do V8 drivers cope? Does anyone fit an auxilary rad, or maybe an oil cooler?

When I had my Cobra, one of the tricks used was to jack the rear of the car up as high as possible allowing any bubbles to move (hopefully) up to the expansion tank. In my beast I had a Transit diesel Rad but you have to realise that, believe it or not the V8 doesnt get very hot.
In my Morgan replica I am building at the moment it has an RV8 in it and I have fitted and MGBV8 Rad in it

Hi Ian.

I just had a thought - I don't know if it's worth trying! A fairly recent development in the 'additive' market is radiator water 'wetting' agent such as Miller's Rad Hib Extra Cool stuff.

I understand it works by breaking the 'surface tension' of water (a bit like adding detergent to a pond and watching the 'Pond Skaters' sink...), which gives the water better contact with surfaces thereby aiding heat transfer. I'm actually thinking it might also in your case make any air bubbles less likely to 'stick together' forming air-locks, and more likely to 'creep' along the sides of the pipes and make their exit! With less surface tension, the air bubbles should break up into smaller ones, and could even be carried out by the water flow until they can exit the way they should!

(If you imagine a drop of water sitting on a water-resistant surface, it'll form a 'bubble' with only a small contact area underneath on the surface. Add detergent, and the water's surface tension is removed and the drop will spread out and flow out. It's been made 'wetter'!)

I've no idea if it would work this way, but it might!