Overheating RP

[Rick F]

I have a problem with my RP, which boils its coolant after less than five minutes at a moderate tick-over when stationary.
 
The story so far:
 
In the past couple of years the car has been almost unused, clocking up only about 130 miles. In June I "borrowed" its carburettor to get the van to Beaulieu, eventually replacing it on the RP.
 
Taking it out on a test run, after five minutes I noticed oil pressure dropping to zero. A quick look under the bonnet showed a massive oil leak at the front end, couple with ominous bubblings and hissing from the radiator. After letting it cool down, I limped home.
 
Stripping the engine down, no obvious signs of damage, other than the oil leaks. No sign of damage to cylinder head or gasket. Big end, main bearings and everything else OK and running freely. Tooth missing on smaller timing gear - gears  replaced.  Block, head and radiator flushed out with garden hose - no obvious blockages.
 
Engine reassembled (silicone gaskets) and installed. Fired first time and ran well with no obvious leaks, then began to boil. Mixture, timing and everything else checked and satisfactory - mixture actually slightly rich. Water seems to be circulating normally
 
Any ideas? Is there a sort of "reverse Radweld" that might flush out an unsuspected blockage? Has anyone experienced anything similar?

[bob46320]

Ignition too far advanced ? Fan belt too loose. How about using a domestic radiator flushing liquid.

[Chris KC]

So the overheating may not necessarily be connected with the earlier oil leak episode?

Halfords will sell you a radiator flush, just check the label for compatibility. The danger is that any scale or rust dislodged has to be removed from the system and simple flushing through with a hose may not achieve this. It's better done before an engine strip down.

[John Mason]

You could try removing the radiator then flushing thus allowing you to move it around tip it upside down and also shake any loose stuff out. Also remove the water inlet manifold and flush from there use a stiff bottle brush in the intake hole to remove anything around the cylinders. I recall flushing my seven radiator etc with the radiator still coupled and when no improvement I removed it and found the bottom tank and outflow pipe full of rusted scale etc.

John Mason

[Chris KC]

You could try removing the radiator then flushing thus allowing you to move it around tip it upside down and also shake any loose stuff out. Also remove the water inlet manifold and flush from there use a stiff bottle brush in the intake hole to remove anything around the cylinders. I recall flushing my seven radiator etc  with the radiator still coupled and when no improvement I removed it and found the bottom tank and outflow pipe full of rusted scale etc.

John Mason

Sorry I don't remember who but someone recently posted a pic of an ingenious temporary tank to replace (and thus save) the radiator while doing this. Might be a bit of work though.

[Rick F]

Thanks chaps.

Fan belt is tight and air is being sucked through the radiator.

Ignition timing is correct  -  advance/retard does not seem to affect the boiling.

Radiator, block and head were thoroughly flushed out while off the car.

[Ruairidh Dunford]

Is the radiator hot all over when you feel the matrix from the front with your hand?

[Chris KC]

An old trick was to mist the radiator all over with water (preferably without shocking it too much) and observe the pattern of drying.

["Slack Alice" Simon]

Cracked block or head,  allowing exhaust gasses into the water?

Check for bubbles in the header tank.

Simon

[Hedd_Jones]

Go to wilcos and buy the cheapest decent sized plastic box you can find. Using a hole saw some araldite and some plastic tube make two connections to which you can attach the hoses to. Swap it with the rad and Fill with water and run the engine.

Your tank cooled engine will demonstrate if the thermosyphon is working. Any bubbles will be visible.