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Old 16th September 2020, 11:26
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Grey V8 Pete Grey V8 Pete is offline
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Join Date: Nov 2011
Location: Exeter
Posts: 172
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Hi! I would offer the following which I hope will solve your problems.
Yes a coolant hose should ideally go uphill from the thermostat so natural convection aids the flow. However you should be ok provided the water pump is in good condition and the radiator and engine are free from sediment build up.

On your pistonheads photo there should be a plain sealing cap on the radiator at 4 so it seals on the top face of the rad boss with no spring or pressure relief. There should only be a pressure cap on top of the expansion bottle 7.

The hose 6 needs to be Teed off immediately after the thermostat housing which is where any air will tend to collect.

Hose 6 needs to be small bore (mine is 8mm) so that as the coolant heats up and expands it will expel any air up into the expansion bottle.

The small bore hose attached to the top neck of your expansion bottle 7 is an “overflow” drain and so should be open ended and finish down under the chassis.

The expansion bottle should not be filled up! Leave about 1” of coolant above the lower connection which should be ample. Keep a check on this after the first few start and cool down cycles and top up as required to replace if any air has been expelled from the system.

Finally I would fill your coolant system from empty as follows:
Remove the plain seal cap from the radiator.
Remove thermostat housing and thermostat.
(I would fit a new thermostat anyway at this time as a precaution.)
Start filling system through the thermostat housing keeping an eye on the open radiator filler hole!
When the coolant level reaches the radiator neck replace the seal cap.
Important! Check now in the workshop manual to see if there are any bleed vents on the engine that need opening to remove air locks.
Continue filling until the coolant level reaches nearly to the top of the thermostat housing.
Fit the (new!) thermostat, new gasket and thermostat housing cover.
Continue adding coolant through the neck of the expansion bottle until it is about 1” above the bottom inlet.
I would then unbolt the expansion bottle from the bulkhead and raise it up for a while so any air bubbles can escape.
Rebolt the expansion bottle in place.
Recheck there is still 1” coolant above the lower connection.
Replace the pressure cap on the top of the expansion bottle.
Start the engine and allow it to warm up, keeping an eye on the temp gauge and check the top hose gets hot when the thermostat opens.

Finally recheck the coolant level in the expansion bottle when the engine is cold.

Hope this rather lengthy post helps. Let us know how you get on. Peter.
P.S I have this layout on my V8 engine and it works well!

Last edited by Grey V8 Pete; 16th September 2020 at 11:28.. Reason: P.S. added.
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