Hello you lovely mechanically minded folk. Need some advice!

I have a 1.8T MK1 Leon Cupra R (MK4 Golf platform) and have cooling issues (sort of).

New parts:
New cooling fans
New thermoswitch (in the rad)
New thermostat Feb 2013
New water pump Feb 2013

Cooling fans kick in when the coolant temp reaches 105oC, and they should (I'm told) kick in at roughly 96oC (temp at thermoswitch in rad). Thermostat attempts to keep coolant temp at 90oC. I have no reason to suspect the coolant temp sensor is faulty as when driving about, the reported temp is always around 87-90oC.

Temp guage in the instrument cluster never passes 90oC, I've read that it's designed to stay at 90oC so long as the coolant temperature is between 85oC-105oC. The only reason I know its different is that I have a liquidguage fitted (via the OBD2 port). The coolant temp only hits 105oC when the car is idling on the drive or stuck in traffic.

The mechanic who fitted the fans wasn't concerned at all that they only kick in at 105oC, but I keep reading that they should be kicking in at a lower temp.

Here's my question: Should I be concerned about the coolant temp hitting 105oC, and if so, what could be causing it? There is a huge issue about slow/fast speed fans but my fans are coming on at slow speed at 105oC, and kick in instantly on slow speed when I turn the AC on. My new fans fix any slow speed issue though I do still have a NIME box fitted by a previous owner (http://www.nime.co.uk/content.php?mk4fans), but this should be irrelevant when it comes to the temp at which the slow speed fans come on.

My only thought is that the coolant temp at the temp sensor and the thermoswitch is nearly 10oC different, maybe due to an air lock or something? When I had my thermoswitch fitted, the mechanic refilled the coolant, but the slow speed fans were kicking in at the same temperature before I had the thermoswitch fitted, so the change of coolant hasn't changed anything, soo I assume it makes an airlock unlikely?

Any help much appreciated!!

Sounds like an airlock to me, yep.

Two fans are there?

Have you considered hooking a fan up to a switch in the car, or an ignition on source, so one is always running..? Little bit pikey to sort it that way, but at least you know you shouldn't overheat.

Can you unplug the fans and manually add a wire to your battery to check they actually have a high and low speed? Sounds to me like it's wired up wrong :S

cheers for the replies guys. Chris, fans spin up when the AC is turned on, so if I got stuck in traffic, I could just turn the AC on (which I rarely use) and it should keep temps at a reasonable level.

Rock, if I bridge pins at the thermoswitch, I should quickly tell whether both low and high speed fans are working. The fans are new (so should be fine) but it is possible the previous owner bodged something when wiring in the NIME box (if so, it will have been like this for years!). If the fans spin up on low and high when I bridge the pins, then I know all the wiring is sound, and its something to do with the temperature readings between the coolant temp sensor and the thermoswitch. Only problem is the thermoswitch is difficult to get to with the car on axle stands. I did ask the mechanic to bridge the pins when he fitted everything, but I forgot to ask him if he did it when I went to pick up the car, so will call and check.

Is the general consensus then that 105oC coolant temperature is a worry?

Bit of an update, and a new question:

I've been sat in traffic a couple of times and have had the cooling fans come on at various temperatures now: 95, 96, 98, 99, 101. So it appeared to be working better.

Today though, I had the fans kick in at 98 while stuck in traffic (car horizontal), then was stuck in traffic on a motorway on-ramp. Car was pointing downwards at this point. I sat waiting for the fans to kick in, but they didn't. liquid gauge got to 107 and the temp needle on the dash started to rise, so I gave up waiting and switched the AC on to force the fans on. Later, on the motorway, I was stuck in traffic again and the fans kicked in at 99 degrees (car horizontal again).

When I tested my car on the drive, my car was pointing up slightly, and the fans didn't kick in till 105.

So my question is; when the car is pointing up or down a bit, does this affect the coolant flow significantly? Should I be concerned?

For me, that just further reiterates what Chris said - an airlock.

An airlock works basically like a spirit level - it's a bubble of air trapped in the top of the cooling system. As the angle of the car changes, the bubble of air will move around. If the coolant temp sensor is inside that air bubble, it won't read anywhere near as hot, so it won't switch the fan on.

I would say you need a good coolant flush (not just a drain and refill), then refill and bleed as per the manufacturers guidelines - with some cars (Peugeot are known for this) you'll need to add a water bottle on top of the coolant expansion tank to "overfill" the coolant system, then open bleed valves on a couple of the hoses to allow the air to escape. Not sure if yours is the same, Google will help you

That's what I keep thinking, but the Seat forum people keep telling me "these cars don't suffer from airlocks - they're self-bleeding". Argh. I've bought some coolant, will just have to give it a go. Wish it was as simple as it is on the F. was just a case of taking the rad cap off and filling up there....

If it's self-bleeding, it is as simple as it is on the F I'd still have a good look over all the coolant hoses in the enginebay, even over the heater matrix ones at the back to see if there is a bleed valve anywhere. If there is, open it and run the engine (while cold) and make sure water comes out bubble-free.

The other issue you could be having, which sounds a lot like my mums 206 in the end, is a headgasket failure - in the case of my mum's 206, we heard a sloshing sound which we originally thought to be water trapped in the sill. I punched that out, nothing came out, then the temp guage started going mad at random times. Did a coolant flush and change, made noise worse, so I bled the system - noise stopped completely. Temp gauge behaved for about a week, then started going mad, then noise came back, and lack of power, and smoke, and some nasty smells.

Garage took the head off and found coolant in 2 of the cylinders

nothing else to indicate headgasket failure....could be dodgy wiring?

Possibly I guess, but I'm leaning more towards something coolant related here

I went back to mechanic and he was very skeptical about an air lock. He thought it could be the fan control module (about the only part that hasn't been replaced recently). On top of this, when the fans do kick in, the exhaust resonates when the engine is idling and I get pulsing vibrations through the cabin. The idle speed determines the speed of the pulse. very annoying!!

Fans kick in, increasing load on the alternator, increasing load on the engine, so ECU throws in more fuel and opens the IAC to allow a touch more air in to keep the engine running at idle speed, so the exhaust will be slightly louder - which is more noticable on sportier exhausts

If you stick it in first, then slowly let up the clutch without touching the throttle, you'll hear the exhaust tone change while the ECU tries to keep the engine at around 750rpm - same thing

May not be an airlock, but I would bet there is something wrong with the cooling system. Fan control module is obviously a possibility, so worth trying a new one maybe?

unfortunately it's not just a change of tone. It's a pulsing......

low idle: just sounds rough. No problem at all, but my car rarely idles low.

medium idle:

wwwwwWWHHOMMmmmwwwwwWWHHOMMmmmwwwwwWWHHOMMmmmm

higher idle:

wwWHOMmmwwWHOMmmwwWHOMmmwwWHOMmmwwWHOMmmwwWHOMmmwwWHOMmmwwWHOMmm

at first I thought it was extra bass beats, as the first time I felt it I had the stereo on, and could feel it through the back of my seat. very peculiar.

just recently had a longlife back box replacing a louder cobra backbox (which broke). This is on the end of a res mid section and 200 cell sports cat.....(not sure if that makes any difference)

itsa bit late now but that sounds like fan control module, they are £60 from Euro car parts, and symptoms sound the same, you have 2 speed fans but the controller is not working so you only have one speed (I've has this on an Audi TT 225 was the last thing we changed). 6 months later so I hope you fixed it by now!