Cooling system advice.

[Paul V]

I had some problems with the car running really rough again when hot so decided to replace the ignition module, I took it for another run and it hasn't played up again, but when fitting the module I notice that the expansion tank had let out some water, I keep an eye on the tank and it's been about half full for the past month with the header full to the top. I let the car cool overnight and checked the water level, the expansion tank and the header tank are now both full, I can't see how there appears to be more water in the system. I took the bleed screw out of the inlet manifold and when I started the car it sprayed water a good 5 foot in the air. Thinking maybe I had a air lock I removed the header thank screw and ran the engine, the water slowly overflowed the tank until I turned the car off when it chucked out lots of water.

I then topped up the they system again, this time a removed the bleed screw first and this slowly pumped water as it normally does, I then out the caps back on and gave the car a run. seems to be running ok now but slightly worried about the cooling system. The car has an Alloy rad and a cerb fan fitted, it sits about 85 on the gauge on a run and drops to approx 75 if I go above 100(shhh) and gets to 90-100 in traffic. This is with a Leven cooling kit added as well, is that normal?

The engine has only done 1200 miles since rebuilt so is not long run in.

To top it all off I have a leaking clutch system too as the fluid is going somewhere TVRs

[simpo two]

Paul V said:

I notice that the expansion tank had let out some water, I keep an eye on the tank and it's been about half full for the past month with the header full to the top. I let the car cool overnight and checked the water level, the expansion tank and the header tank are now both full, I can't see how there appears to be more water in the system.

I'm not an expert but I think you're worrying too much. If by 'header' you mean swirlpot, leave it alone. As for the expansion tank, that should be half full when cold. The very title should tell you that it caters for expansion - ie the level can change. My humble advice after 8 years of Griff ownership is to stop fretting and take the approach that if it works, leave it

[Paul V]

You could be right, I'm probably being over protective of the rebuilt engine but seeing as it is the 3rd rebuild since owning the car you can understand why I took it for another run today and it seems to be running better with the new ignition module in place.

[GreenV8S]

Paul V said:

I took the bleed screw out of the inlet manifold and when I started the car it sprayed water a good 5 foot in the air.

Good, getting water out shows the engine has been bled properly. I suggest you bleed the radiator too. If the engine has been drained recently then you should do this again in a couple of weeks time because it'll take a while to chase all the air bubbles out of nooks and crevices.

The system needs a certain amount of air in it to act as a spring, to cope with thermal expansion and hoses stretching etc. If you over-fill it, without the springiness the system will go over pressure and spit water out. But it's important that the air is in the right place - it has to be in the header tank, not the engine or radiator.

[Paul V]

All the air appears to be out of the system but I took the car for a little spin and it is ok while moving but after just a few mins in traffic the car went up to just over 100 on the gauge, it never went that high before the rebuild, even while sitting in traffic in Italy. I checked the temperature with a digital thermometer and the gauge appears to be accurate to approximately 5 degrees C.

[GreenV8S]

Is the fan coming on, is it blowing air the right way, is the air coming out hot?

[Paul V]

Yes both fans are working, they are connected correctly and both sucking air rather blowing, the air is hot also. I have measured the temperature of the top hose using my infra red thermometer and it is about 5 degrees higher than the gauge is reading, this I assume means the thermostat is opening correctly as the water appears to be flowing.

I assume the bottom pipe should have cooler water flowing in it as it should have been cooled by the fans? Any idea what temperature that should be at so I can make sure the rad is cooling sufficiently. The rad was second hand but was fitted to a twin turbo Griff, so shouldn't have a problem keeping a standard car cool.

[GreenV8S]

Paul V said:

Yes both fans are working, they are connected correctly and both sucking air rather blowing, the air is hot also. I have measured the temperature of the top hose using my infra red thermometer and it is about 5 degrees higher than the gauge is reading, this I assume means the thermostat is opening correctly as the water appears to be flowing.

I assume the bottom pipe should have cooler water flowing in it as it should have been cooled by the fans? Any idea what temperature that should be at so I can make sure the rad is cooling sufficiently. The rad was second hand but was fitted to a twin turbo Griff, so shouldn't have a problem keeping a standard car cool.

The top hose temperature tells you the stat is opening (or leaking) but not that it is opening fully. You need to check the bottom hose temperature to see if you have enough air or water flow. You will typically get a temperature drop of the order of 10 C across the radiator at tickover with the fans on. If the drop is bigger than this then you probably don't have enough water flow. If the drop is a lo less than this then you probably don't have enough air flow, or you are suffering from hot air recirculation or some other problem that is preventing hot water in the radiator from seeing cold air (for example unshrouded fans, or a scaled up radiator, or an air lock). Can you stick your hand in front of the rad and feel whether the air being sucked into the rad is noticeaby hotter than ambiant? It's quite common to get hot air from the back of the radiator sucked back under the car and through gaps round the edge of the radiator and get pulled back through the radiator. This hot air recirculation directly drops the cooling capacity of the system i.e. 10% hot air recirculation reduces the cooling capability by 10%. In other words, hot air recirculation is very bad and well worth eliminating.

Edited by GreenV8S on Tuesday 19th September 12:18

[Paul V]

The fans are unshrouded I'll go measure the temperature of the water leaving the rad, I could make up a shroud for the fans if that is the problem, but it was running like that on the previous car and I would imagine that would have caused more problems than mine?
It's hard to get to the front of the rad as I have an air con condenser in front of it.

[Paul V]

ok I'm only seeing a drop of about 6 degrees from one side of the rad to the other.