Okay,

Bit on the warm and humid side today and fairly heavy in slow-moving traffic. Had to do an errand, and after 1/2 an hour I noted the temp gauge went above the mid-point - surprised, so pulled over straight away. [Will be ordering one of those engine savers in the not too distant future!]

Took the acoustic cover off and noted the leak from the front of the fuel cooler (the older shell/tube design with the plastic end caps and FKM (Viton) seals). The expansion tank was empty.

Let things cool a wee bit and then put OAT coolant in the expansion tank - took about 3L to get it up to level. [Didn't raise the expansion tank though.] Started driving home and after 20 min it had just crept up again. Turned the heater on full bore - fan blowing, but no hot air coming into vehicle as you would expect. Assumed trapped air in the system - there was popping creaking noises I could hear from inside the vehicle with the heater on so figured that was air trapped in the hoses. Pulled over again.

This time I unclipped and lifted the expansion tank 3-4 inches above where it sits (unclipped hose from radiator - don't want to break those!). I removed/undid the brass coolant bleed screw/nut at the top front of the engine. I then started the engine and put the heater on full heat; I topped-up the raised expansion tank and after 10 seconds, coolant shot up 2-3 inches from the coolant hose bleed. I assumed all the air was out, so put the bleeder screw/nut back in firmly, lowered the expansion tank, topped-up the coolant level and put the expansion tank cap back on.

Got home (another 15 min), but when I stopped the engine the electric fan was running for a little while. Temp gauge at mid-point.

So, obviously need to do that leaking fuel cooler again! With the o-ring at the front of the end cap I can't seem to push it in all the way so the black plastic tabs on the end cap go all the way to the back of the four slots in the steel body!

It looks like I still have air in the system (at heater) as the heater air is not hot. Just bleed again after "fixing" the fuel cooler? Any thoughts/ideas?

I had niggling small leaks, small splits in hoses, etc. but also the coolant system pressurised quickly (hard top hose).
This turned out to be a classic cylinder head dowel failure.
I say this only because it could potentially be very early stages so now is the time to diagnose and fix it and save any bigger costs.
What was the top hose like when squeezed?

Bantam1 said:

I had niggling small leaks, small splits in hoses, etc. but also the coolant system pressurised quickly (hard top hose).
This turned out to be a classic cylinder head dowel failure.
I say this only because it could potentially be very early stages so now is the time to diagnose and fix it and save any bigger costs.
What was the top hose like when squeezed?

Click to expand...

Top hose is/was soft - I put a new hose on 2 years ago; no gasses or milkiness or any issues with coolant colour.

Intestinalworm said:

Top hose is/was soft - I put a new hose on 2 years ago; no gasses or milkiness or any issues with coolant colour.

Click to expand...

If sure then thats good news, saves a whole heap of work. Not that its difficult its just heavy and time consuming.
I guess after fixing the leak just bleed well to get heater clear of air then. Never had a fuel cooler leak so cant comment on that.
As you have already suggested, sit expansion tank up above radiator. I fill the last bit from the expansion bottle letting the air and some fluid out via the top hose bleed screw until level is correct. I then reinstall the expansion bottle cap before sitting it back in its holder.

Intestinalworm said:

Top hose is/was soft - I put a new hose on 2 years ago; no gasses or milkiness or any issues with coolant colour.

Click to expand...

I think at the back of the fuel cooler, the coolant branches off to the heater core, so I'm thinking with the coolant draining down to the bottom of the fuel cooler that there are slugs of air in those hoses and the heater core - may be this was why with the heat to max and the fan on max that the air was not hot.

The bleeding procedure from RAVE is a bit incomplete IMO, to bleed it 100% you have to let the bleed screw partially tight as to still have some flow there and keep the engine running at 2000rpm untill no bubbles are coming out then tighten the bleeder completely. This is necessary as the bypass valve in the thermostat is mechanical and opens above 1500rpm only so without that trick there can be an air lock on the bypass circuit which is in direct relation with the heater circuit

By-pass flow valve

The by-pass flow valve is held closed by a light spring. It operates to further aid heater warm-up. When the main valve
is closed and the engine speed is below 1500 rev/min, the coolant pump does not produce sufficient flow and pressure
to open the valve. In this condition the valve prevents coolant circulating through the by-pass circuit and forces the
coolant through the heater matrix only. This provides a higher flow of warm coolant through the heater matrix to
improve passenger comfort in cold conditions.

When the engine speed increases above 1500 rev/min the coolant pump produces a greater flow and pressure than
the heater circuit can take. The pressure acts on the flow valve and overcomes the valve spring pressure, opening
the valve and limiting the pressure in the heater circuit. The valve modulates to provide maximum coolant flow through
the heater matrix and yet allowing excess coolant to flow into the by-pass circuit to provide the engines cooling needs
at higher engine rev/min.

Okay, all bled perfectly now (thanks sierrafery) - no air and heater all good - went on a 120km round-trip today and level spot on. Fuel cooler well and truly fixed now - not a drop of leaking coolant! Made sure the black plastic end cap was pushed home all the way this time so the four black plastic tabs cannot go any further back in their slots - gave enough room for the 9mm wide narrow band jubilee clamp I used. This time I put the new FKM (Viton) o-ring in the inner most channel/groove and also put the old original o-ring (flattened) on the outside channel - there are three channels/grooves, but only one o-ring used in the original Land Rover set-up. This time around I lubricated the o-rings well with Herschel red rubber grease, and also lightly smeared it around the plastic end cap and the inside of the cooler body. I aligned the plastic cap well and gave it a firm push, followed by several small, swift taps with a small hammer onto a small piece of wood place over the end cap spigot - it went in perfectly this time and was very snug! Removing the expansion bottle gave me a bit more room to move and use the small hammer to good effect. Also, this time around I used the jubilee clip - previously I had re-used the LR original r-clip - no good - could spin it around with my fingers!

I don't want to get caught out with an unexpected (and potentially catastrophic) coolant leak again so I'm definitely going to get an Engineguard or similar (check engine and transmission temperature) when I get a few spare bob.

sierrafery said:

The bleeding procedure from RAVE is a bit incomplete IMO, to bleed it 100% you have to let the bleed screw partially tight as to still have some flow there and keep the engine running at 2000rpm untill no bubbles are coming out then tighten the bleeder completely. This is necessary as the bypass valve in the thermostat is mechanical and opens above 1500rpm only so without that trick there can be an air lock on the bypass circuit which is in direct relation with the heater circuit

By-pass flow valve

The by-pass flow valve is held closed by a light spring. It operates to further aid heater warm-up. When the main valve
is closed and the engine speed is below 1500 rev/min, the coolant pump does not produce sufficient flow and pressure
to open the valve. In this condition the valve prevents coolant circulating through the by-pass circuit and forces the
coolant through the heater matrix only. This provides a higher flow of warm coolant through the heater matrix to
improve passenger comfort in cold conditions.

When the engine speed increases above 1500 rev/min the coolant pump produces a greater flow and pressure than
the heater circuit can take. The pressure acts on the flow valve and overcomes the valve spring pressure, opening
the valve and limiting the pressure in the heater circuit. The valve modulates to provide maximum coolant flow through
the heater matrix and yet allowing excess coolant to flow into the by-pass circuit to provide the engines cooling needs
at higher engine rev/min.

Click to expand...

This is so important it should be printed in big letters in RAVE and the Haynes manuals.
We get this issue so often on here.
Don't know where you got this from but brilliant that you did and are posting it.
Well done!

Stanleysteamer said:

Don't know where you got this from but brilliant that you did and are posting it.

Click to expand...

I should have registered this trademark cos i figured it out myself after reading how the system works

Thanks all! Thanks sierrafery! It is quite often the case that the Devil Is In The (overlooked/unmentioned) Detail! Also, near enough is quite often just not good enough as I found out! You must find a way of pushing that end cap ALL the way home - getting better access by removing the expansion tank, using the Herschell Red Rubber Grease, and using a number of swift, but fairly gentle taps with a small hammer (small upholsterers hammer) and a small block of wood (didn't want to crack the plastic end cap!) did the trick! And, I know the original spec r-clips are supposed to be reusable, but not mine - looked alright, but I slipped it off with my fingers! (Also, I now have a AUD 11 pair of r-clip pliers that may come in handy later on!)

All is well that ends well!

So now I've done the front end of the fuel cooler twice! This time around it's spot on, and not just near enough - if there's a small drip then it can only get worse!

In the end I decided to just leave the rear end cap though - it hasn't leaked a drop in 17 years (original o-ring and r-clip). To get the fuel cooler off completely as far as I could see the two bottom 10mm bolts are not accessible from above - best done from underneath reaching up, ideally with a ratcheting ring spanner (which I don't have). As is often noted, perhaps the coolant hose on the front end puts a slight load on the end cap and exacerbates the issue of a flattened and less supple o-ring?

Anyway, have another FKM (Viton) o-ring and narrow band jubilee clip for the rear end if it ever decides to leak!