Overheat query

[DaveH76]

Thanks guys. So in a nutshell Geoff - pinhole leaks are a pain in the arse to find....!! Brilliant

Haydn - thanks for the tip. I have looked at the egr pipe flange where it meets the air intake and it doesn’t seem too bad, and the flange where the air intake pipe bolts onto the plenum chamber seems ok too as does where the manifold bolts to the head (no oil being purged out between the mating surfaces). I haven’t checked the egr valve itself though so thanks for that, I will certainly give it a look over.

[Bob]

Check out the UV kits Geoff recommended.

https://www.ebay.co.uk/itm/UV-Dye-Torch ... SwJ7RYWWhQ

[DaveH76]

Will do, thanks Bob. Just spent an hour on it giving it a good look over. I can’t see any obvious signs of a leak but it definitely has air in the system.

I reckon the next step is going to be to drain the system, remove and backflush the radiator and the engine (the coolant is really brown rusty colour), refit the radiator, and fill, bleed, and add the UV dye.

Thanks guys, much appreciated

[haydn callow]

When you flush push some water ‘up’ the system vis one of the rear heater rad pipes.

[DaveH76]

Thanks Haydn, will do. I take it that this is to flush the rear heater matrix? Or do you mean flush back from the rear heater matrix to the radiator?

I was also considering putting some coolant system flush in after I have found and rectified the leak. Anyone had any horror stories with doing this?

The UV dye arrived today so I will bleed the system and add the dye to see what happens.

[haydn callow]

It’s to flush back !

[DaveH76]

A bit more advice if I can please....!

I have finally got around to bleeding the coolant system (combination of full-time work, University study, kids, half term holidays...!). The coolant definitely needs replacing but that will be last job after I have found and rectified the leak.

I am 100% sure I have bled the system properly because I have had both top and bottom hoses hot and had heat coming from the front and rear systems. The bottom hose took a while to get hot so that, to me, indicates the thermostat is present and operating.

When the engine has been up to temperature I have been holding the revs at 3000 rpm to try to get the cooling fans to cut in, but instead of the fans coming in the fan in front of the engine (scavenger fan?) has been cutting in instead and the glow plug light flashes.

I know that the fans on the radiator work because they both come on when the A/C system is engaged, so am I correct in presuming that the scavenger fan is cutting in as a safety back-up and there is an issue with the cooling system bringing in the fans (currently thinking the fan switch or the fan switch relay is kaput)?

Thanks guys.

[g8dhe]

The scavenger fan is operated by a thermistor mounted in the engine compartment just below the handbrake handle, its not for cooling the coolant itself its for forcing air into the engine compartment to remove heat coming from the head and trapped inside the engine compartment, normally the air flow from moving keeps this cool. However when static in a jam or when bleeding the coolant system the engine compartment gets hot and hence the fan will cut in.

[DaveH76]

Thanks Geoff. I thought that was the case with the scavenger fan, but I had the centre panel off and over to the back seats so the thermistor you mentioned was unplugged (along with the other connections on the panel) which leads me to think there’s a second use for the fan (I.e. if the radiator cooling fans fail)?

Is it normal for the scavenger fan to cut in before the radiator fans? And if the scavenger fan cuts in then is it normal for the glow plug light to flash?

[g8dhe]

Yes if you unplug the thermistor then the ECU assumes sensor failure and turns the fan on for safety! Hence the glowplug flashing as its reporting an error.

[DaveH76]

Thanks Geoff. So I am presuming that what I experienced is normal:

1 - Thermistor unplugged, engine running, coolant cold, scavenger fan not running

2 - thermistor unplugged, engine running, coolant up to normal operating temperature (top and bottom hoses hot), scavenger fan not running

3 - thermistor unplugged, engine running, revs raised to 3000 rpm to increase coolant temperature to get the radiator fans to start but instead the scavenger fan kicks in and the glow plug light flashes

I have seen other mentions on this forum regarding unplugging the switch on the offside of the head and all fans (scavenger and radiator) engage so I will try this tomorrow to check.

[g8dhe]

It seems to be along those lines yes. No one has actually disassembled the code in the ECU to see what has actually been written for, but plenty of reports of the scavenger fan coming on when the engine is on and been running, it will also come on even if the engine is off but hot I suspect. Its not helped that there seem to be several generations of actual ECU code across all the vehicles!

[DaveH76]

Thanks Geoff.

I think I need to investigate further why the radiator fans do not come on then. I know they work and the relays are OK because they come in when the A/C is engaged, so if the head-mounted fan switch is working fine then it’s pointing to a wiring issue.

[g8dhe]

They don't come in till quite late in the day here is an animated GIF of the process;

[DaveH76]

I’ve seen that GIF before which is really good! If it had the scavenger fan operation on it to then it would be even better (easy for me to say )