Gti6 Conversion With A Strange Cooling Problem

[HERMAN 33]

Right engine is fitted, all plumbed in with BBM hose kit and thermostat housing adaptor. I have ran the engine up to temp several times. Slow fan kicks in cools it down, all good no drama's.

If I hold the revs on (say 2000 RPM) then the expansion tank fills up with in a few seconds with coolant. (the coolant looks quite aerated/ fizzy).

I have tried bleeding it of air at the stat housing/ heater matrix joints and rad top hose.

If I let it drop back to idle the coolant level drops back down.

I have pulled the heated hose of off the matrix (the hose from the stat housing not the hose from the back of the block near the pump) and coolant is being pumped out from the engine at the stat housing point with plenty of flow.

From my working out then

The coolant is sucked into the pump from the bottom of the rad/ heater matrix and expansion bottle at the back of the block, then pumped through the engine and out at the thermostat housing and into the heater matrix until the thermostat opens, then most of the coolant goes through the top hose through the rad and then back into the bottom of the block at the rear.

Does this sound correct?

I don't think that it is the head gasket because it will happily tick over hours on end and does not make much pressure.

There also does not appear to be any coolant returning to the expansion tank via the small hose off the top of the rad.

Note it is fitted with a brand new rad, all new hoses, new water pump,

Any Idea's please.

The car is not on the road or I would take it for a run out. Not finished the body work or MOTed yet.

Thanks

Neil

[Richie-Van-GTi 72 2 Cars]

Do you know anyone locally with a sniffer test? Could be worth a quick check after making it 'fizzy'. It does sound very much like a slight blow in gasket apart from the level settling back down part. The small hose generally wont return anything other than excess air as its too high in the system. Has the overall level dropped at all?

[Peetypug 5]

have you got a gti6 header tank cap on it? the 6 cooling system runs at a higher pressure than the 8v

also try undoing the top hose from matrix and making sure it isnt air locked

 

both these were problems for mine last week

 

rad cap was about £5 from a motor factors

 

hth

[HERMAN 33]

I think I may have worked it out.

Just ran it up again and the problem is only there until the thermostat opens. Then it all seems fine.

I am suspecting the heater matrix is blocked or restrictive and causing a back pressure in the bypass circuit.

I am going to join the matrix hoses together tomorrow when it has cooled down and see if the cures it till I can get a matrix.

The heater was giving out some heat but not as much as I would expect for the heat that was in the engine.

Thanks for you ideas lads I will let you know how I get on.

Cheers Sorrentopete I have got a GTI6 rad cap fitted.

Thanks

Neil

[Alastairh 47]

have you got a gti6 header tank cap on it? the 6 cooling system runs at a higher pressure than the 8v

also try undoing the top hose from matrix and making sure it isnt air locked

 

both these were problems for mine last week

 

rad cap was about £5 from a motor factors

 

hth

 

Be careful here. On tests I done a genuine 306 cap didn't seal 100% on a few water tanks I tried. I would go for an aftermarket cap. Personally I'm not all convinced by this t piece setup.

 

Al

[tony perks 1]

if no good try drilling a 3mm hole in edge of thermostat, so water can at least circulate until stat opens.

[Miles 331 1 Cars]

As said the 306 cap I don;t think fits well at all and the std one is fine, water set up is spot on.

I'd check the H/G, I know on a very old car of mine not until the rev's rose did the water come out, On tick over etc the leak was so small it all looked normal

[welshpug 1,657]

if you do want to run the higher pressure 306 cap, you need to trim off two tabs from the cap.

 

Edited November 11, 2010 by welshpug

[marksorrento205 80]

I have ran the T peice bbm hose for 15k with no issues

[2052006 10]

I've got it set up like the 8v plumbing, so no T-pieces. Tried using the 306 cap at first, but it leaked. Switched back to the original 8v cap and it's never leaked. (Though I never tried modifying the 306 cap as WP suggests).

 

As for engine temp - it's always been spot on, even on trackdays, and never seems to even go up to the fast speed on the fan.