New 4L engine in SD1 water was pressed out of the filler cap

[Kassi]

Hi,

The new 4L engine was driven now for 2000 km and runs very well with SU carbs. No water in cylinders I could find. With new waterpump and thermo coupling, now a new 75° thermostate and new filler cap keeping 20 psi. Every time the engine warms up, short before thermostate opens, water was rising into the expansion tank up to the cap and have been pressed out. Shortly afterwards the engine is sucking in the residual water heavily. With my changes mentioned above, the problem has nearly stopped, but when I in addition have opened the heating, it happends again. What I found out, is that the 4L engine block was different regarding the water channels, in front, from the block to the cylinder head, they are much larger than for the 3.5 having only small bores in the block.
It seems to be the small water circulation does not work properly?

[ramon alban]

Hi,

Every time the engine warms up, short before thermostate opens, water was rising into the expansion tank up to the cap and have been pressed out. Shortly afterwards the engine is sucking in the residual water heavily.

It seems to be the small water circulation does not work properly?

Kassi, Its possible air is trapped in the system. This might resolved by fitting a bleed valve high-up on the cooling system.

Alternatively, try this method of filling a cooling system without air locks:

http://www.vintagemodelairplane.com/pag ... ant01.html