Running without a thermostat is not a good idea, or if removed a restrictor should be fitted.
The reason for this takes a bit of thinking about.
The water temperature in the head and around the exhaust valve is extremely high and with the stat removed the boiling point is reduced as the pressure is controlled only by the temp and pressure cap and runs at about 6-10 psi.
The thermostat acts as a flow restrictor at the head outlet and allows the pump to build pressure in the head to 20-30 psi raising the boiling point and allowing more heat to be removed from the head and helping to stop localised boiling around the exhaust area.

I hope this helps.

I'd be surprised if the water pump is capable of creating a pressure of 14-20 psi, the fins on it are quite small and big gaps around them. More of a whisk than a pump!!

The thing is it's not a new build, so having a thermostat before was ok if I take it out i'm just compensating for some underlying problem.

A while ago I added a small bypass hose to allow the air to vent out of the top of the heater - it goes to the expansion tank. I could revert that then I'm back to the same configuration as I've had for 10 years.

I'm convinced to high oil pressure is linked to then overheating issue. It's all very odd.

You would be surprised what the pump can do in a correctly designed system.
25-30 PSI should be produced when the engine is under load and the heat produced in the head is extreme.

The pics show the effect of the pump, the pressure gauge is fitted just before the thermostat. Surprised or what............?

yep - very surprised. I guess that means that if the header tank was on the wrong side of the pump then the cap would be opening under that pressure.

I'm sure mine is ok but I'm not sure about the extra pipe I added.

As an aside - I have noticed over the many years I've owned it, a build up of waxy crystalised stuff by the header tank cap. I assume this is the remains of antifreeze after it's dried out.
Do you know if that could be within the engine as well (or only where it meets the air)? and is there a flush that would clear it out?

It could be contributing to the problem as well.

Sorry Keith I probably haven't explained it very well.
As the open thermostat creates a restriction, the pressures shown are between the pump and stat. As the coolant flows through the stat the speed increases and the pressure drops to normal temperature created pressure (approx 6-10 PSI).

Your extra pipe could be causing a problem, unless it is 'balanced' (offering the same resistance as the system) the coolant could be using it as the easiest route and reducing flow elsewhere.

Unless you have been using 30% antifreeze oxides will have built up in the waterways and it has been noted that 12 thousands of an inch deposit can reduce heat transfer by up to 40%..............scary or what.........

There are plenty of system flush products on the market, how well they work will be suck it n see.
If I needed a system clean my personal choice would be.

http://www.sentinel-solutions.net/product/detail/central-heating/liquids/x100-inhibitor/

I hope this helps, if you have more questions please ask me to mail you my phone number as my first digit is suffering RSI......

Hi Mel, Thanks for the info.
There are a few things for me to try. I'll let you know how it goes but it will take a while as I'm busy fixing the house and other cars.

I am afraid it sounds a fundamental engine problem. I suspect either porous heads or a combustion leak past the liners. Also I fear that the engine will not like being boiled up too many times.

We took a 3.9 to Spain and it kept boiling. I solved the problem with a Range Rover header bottle. Catch the gas, separate it from the water, let the gas out and send the water back to the cooling system. Worked a treatfor next years rally to Rome.

Also I had a 3.5 with no apparent problem at all by way of head cracks, but replacement heads and the header tank did the trick. Somewhere there is a video of my hysterical laughter at the needle way into the red doing the Pyrennean hairs pins. A liter of water at lunch time another in the evening.

Hope his helps.

Nigel Brooks
Findhorn Cars
01730 823647

Hi Nigel

It's getting to the engine rebuild stage!!
I'm in the process of doing the head gaskets and I'll check for cracks in the heads and block too.
Do you know where they typically crack.

It's a bit diasapointing really as its only done 20k miles and I'm too busy to spend much time on it these days.

I'll report on any findings as I go !!

Keith

Very interesting, could the 'gas' be localised boiling of the coolant that the tank removed without solving the problem?

or its a slight head leak, like I suspect with mine. As my car and v8 has run well for >10 years I think the actual design is ok. So it's a fault thats developed which needs finding and fixing rather than some redesign work.
The header tank idea is interesting but the cooling system is supposed to be a closed system. My un-physisist thining is that if air is getting in or steam created then something has to come out somewhere.
Did you have to top up water regularly?

Help us out here Nigel, where did you find the problem?
|It looks from your posts that the header tank position removed 'gas' from the system and would help in saving the heads as the 3.5 was ok after. Info please, please..............please.

Looks like our request for help has been overlooked Keith, a pity as the cooling system on a high power car with minimal frontal area to remove heat needs all the input we can get to understand it, make it work efficiently and possibly improve it..
Regards Mel.

Hi Mel

The V8 cooling is generally a troublesome area. I've heard so many "interesting" methods to "improve" or "fix" it.
I think the actual way it works is missunderstood - I once found a website that described how the flows actually go round the system. Not sure if I can locate it again, but it was quite good.

The problem seems to be that lots of so called fixes are made to try and correct either a fault that itself should be fixed, or some fixes just try and cure a bad installation.
For my fault, I'm not going to change the cooling system or add odd ideas to catch bubbles of air. The cooling has worked for 10 years plus so it's not suddenly become a bad installation that needs additional parts added.

One thing that does hinder the cooling is the fan on the front of the rad. A long time ago I spoke to Kenlow and they said that the fan is best on the back of the rad (sucking air through) as the fan on the front causes a lot of disruption to the air flow and above about 30mph actually is not effective, I guess the air pressure of the car moving is more than the fan at higher speeds.

The other thing I tried was "wetter water" but the effect was minimal.

I've not advanced on the heads much due to other stuff but so far nothing looks broken. I'll keep you posted.

Keith