Overheating

[David J]

After 18 months work rebuilding an old Dax I finally started the engine today (bog standard Rover V.
Brilliant, good oil pressure and all the dials did the right thing.
One problem, it overheats and boils.
I have taken the pipe for the expansion tank from one of the heater pipes (the one without an on/off tap-its the highest point on the engine) and fitted an air bleed valve to the top radiator pipe as close to the thermostat housing as possible.
I have completed several cycles of: start up, open up the air bleed until water comes out then shut it . Each time the system then begins to pressurise, the temperature gauge shows +- 100c and the
expansion tank is full and the pressure cap starts venting water.
Could this just be a duff thermostat or have I got the expansion tank take off point wrong or what? Any ideas?
David :}

[r0lex]

I would be tempted to take out the thermostat and try it with out one. see if that makes a difference.

If not then the next thing i would do is panic.

r0lex

[euro_427]

I hate to be a voice of doom - but the last time I had something similar, it was a distorted cylinder head allowing the gasket to blow, thereby putting hot gases into the cooling system.
Q: Have you done a compression test on all your cylinders ?
IMHO - I recommend doing that as a priority, before wasting time on other avenues. At least if your cylinder pressures are good, it gives you a good point to continue from. If one or more cylinders is/are low on pressure, head must come off and be checked, and if you are lucky it will only need a new cylinder-head gasket to give you a smooth running and 'cool' engine.
Best of Luck
Graham H

[Steve Senior]

Here is a bit of a brain dump. Rovers overheating are a common problem.

Air in the system – Make sure your expansion tank is the highest point on the system. The pipe out of the thermostat is high and just the right shape to cause air lock, try squeezing it to push any air out of this section when it’s hot and the thermostat is open, and also make sure pipes to the heater are clear of air

Thermostat not opening – test it in a pan of water, you can run without the thermostat for a period but your engine will run cold and it won't do it much good

Fan not working, this will be required when stationary

Radiator blocked – very possible if it’s been stood a long time. You could try these flushing agents but I never found them very effective and as a radiator is cheaper than a new engine, invest in a new/recon radiator if you suspect it’s blocked. When you first flushed the system, if the water was very rusty I’d change the radiator

Timing – has been known to cause problems, 8 deg is a good starting point and check it advances when you rev it

If you fill the expansion tank full when you first start the engine it will blow out the excess as the system expands and the air is flushed through, as long as your expansion tank is 2/3 full when it cools don’t worry about that too much. If it’s lower than that there is probably air in the system which obviously expands more than water.

And finally check your temperature gauge, ideally by removing the transducer and dropping it in boiling water ( a kettle) and see what your gauge reeds

Hope this helps

Steve

[maxGD059]

I agree. Taking the 'stat out is the easiest & quickest way to see if there's more to the problem.

Cheers

Richard
(Hillclimb convert)

[martin]

I had exactly the same problems with my RV8. Checked the compression ratios - OK, tested the themostat - OK, drilled a pair of 5mm holes at the top of the thermostat to help bleed the system, raised the header tank as high as possible, - still the same overheating after a few minutes running. However i noticed cycling the heater controls delayed the overheating a bit. Took out the thermostat and all works fine. So am putting it down to air locks in the system, RV8s seem notorious for this.

[David J]

Thanks for all the advice.
I've taken out the thermostat and had a really good go at getting the air out. I've also put the fan on manually when the temp. gauge reads 75 and thats keeping the temperature constant at idle for about 15 minutes so I think its a combination of air lock//duff thermostat /?change fan switch.
Two questions:
What is the "normal" hot tick over temperature
The fan switch is coming on at 95oC (measured in a pan of water)
Would it help to get one coming on at 87oC?
David

[r0lex]

my fan comes on at 66c kenlow

r0lex

[martin]

I use an adjustable one, capillary type with the sensor inserted into the top hose by the radiator.

[Steve Senior]

I fitted a thermostat that opens at 82 deg, drilled a 6mm hole in the top to help get air out of the system. The fan is set to come on at 90 deg and the engine never goes above 92 even in town in this weather
Steve