Capri water pump set-up.

[Mutly]

I,ve just fitted my own version of the external 3ltr. Capri water pump set-up & I,m getting serious problems with the coolant system over pressurising...I,m using the unused large vee belt drive on the crank pulley...is the pump spinning to fast ?...anyone done something similar...what am I doing wrong.

[flying farmer]

Water pumps deliver very little pressure but a lot of flow, I would suspect an air lock in the system somewhere.

Or your head gaskets are on their way out.

What was it doing before you changed the pump?

[Mutly]

I have done a gas test & no head gasket leaks...bled the heads from the rear & at the rad. all seamed ok...it was on the std. pump but as I was making a couple of changes I decided that, just in case i would build an external pump...it,s back on the std. set-up & ran for 20 mins. no probs.

[AndyG]

Silly question but was the old pump removed when you installed the external there is a bung that goes in its place to seal the holes. Not sure of the effect of having both pumps in place ?

[Wheelz]

Overfilling the system so as it heats up there is no air gap for the coolant to expand into?

Note: The pump only creates a pressure (head) between the pump inlet and outlet, it does not affect the pressure in relation to atmosphere.

[jbuckl]

All things being equal (big assumption) either an air lock or thermostat problem will cause this.

However that is taking everything else on face value.

How is the bypass plumbed?
How is the original volute blocked?
many more questions too.

Have seen a very nice capri pump install (diy) done on the left side… clearances all considered, roadside pump swap would be really simple to do etc etc.

[Mutly]

I have now converted back to the origonal set up after rebuilding the Triumph water pump...12 vane...it,s doing the same thing....excess of bubbles in the coolant & the hoses are rock hard...the engine is NOT overheating...it is over pressurising...checked for compression leakage into the coolant system & there is none...this is happening on a brand newly rebuilt high compression engine.

[trunt]

More questions..

Mk1 or Mk2?
what pressure radiator cap do you have?
Is it spitting coolant out of the cap?
How and when do you see bubbles in the coolant? When hot? Cold? Where are you looking?

[NeilR]

As its a newly rebuilt unit, have you re-torqued the heads since it's been run up to temperature ?
What head gaskets were used & was any sealant used ?

[Mutly]

The heads have been re-torqued to 65 lbs/ft...I used Rimmers std. thin head gaskets as I wanted to increase the compression ratio & used Kent uprated camshafts...no sealant was used on the head gaskets...allthough I,ve since read that it,s a good idea to coat the gaskets with Welseal.

[flying farmer]

Is the cooling system still under pressure when the engine is stone cold?

This obviously requires the cooling system to be leak free. If the answer is yes then its a head gasket problem. If you are not sure the system is leak free it is possible to pressure test the system. I used an old tyre valve pushed onto the expansion tank spigot on the radiator and held in place with a hose clip. I then used a bike pump to pressurise the system.

i once had a problem with the Rimmers gaskets, the fire ring didn't compress enough to allow the gasket to seal the waterways. some years ago now and it might have been a bad batch. I now only use the BGA gaskets and have had no problems with these.

If your cooling system is pressurising, you have probably checked the heads for straightness, but did you check the block?
My first Stag had 3 sets of head gaskets fitted in 15000 miles according to its history file when I bought it. Following an unrelated blow up, I found both sides of the block needed 8 thou skimming off them to get rid of the warp between the rear cylinders and the waterway.

[jbuckl]

Have been following.

Try a cylinder leak down test.
compressed air (100-150psi) down all plugs on tdc valves closed. Must be at precisely tdc otherwise pressure turns the engine.
switch pressure off & watch pressure decay vs time.
Pita but worthwhile.

Have you checked the the thermostat?… thinking it maybe stuck closed or incorrectly fitted.

Which parts did you use in the 12v pump rebuild? Not related to your current issue, but poor parts are available & cause big issues.

the seal Ld part offers has been changed for correct spring rate.
Revington TR stock an OEM seal…. (Pioneer Weston 3155)

Most of the rest ‘fit the hole’ but cause a high torque to turn and potentially skew gear failures. Torque to turn the pump target 1.0 Nm.

I built a pump with all available seals to measure this.
Results were shocking….
Motivation was 3 skew gear failures.

[Mutly]

Flying Farmer, Yes the engine is under pressure from cold...pressurised the cooling system started the engine & immediately it jumped to25 psi...did a compressure test & was a bit disappointed...110 was the highest reading...after building what I consider a higher performance engine I thought the readings would have been higher...I,ll check the cylinder head height tomorrow.... the valves were plastercine checked to test piston clearance & were a good 2mm...even with the problems the engine sounds fantastic.

[wilf]

Sometimes, with high performance (.e. large duration/overlap) cams, you get lower compression test figures. You did say you had fitted some such, although I didn't know Kent cams did them for the Stag.

[Mutly]

Wilf, They are just a regrind on the STD. cams...give a bit more lift but everything stays the same...nobody does proper high lift cams enymore.