2007 CLK 220Cdi temperature gauge erratic showing high and limp home mode.

[Droverunner]

Mrs D has just phoned having driven over 80mls into a 100ml trip... so thankfully only 20mls from home... when she noticed at 75mph on the motorway on her usually well behaved CLK the temp gauge had risen to 120 from its normal 90. I got her to pull off the motorway and check water wasn't streaming out of anywhere, the drive belt was intact and the header tank was full. Indeed all looked OK. She did a video call and at idle I could see the temp gauge indication was bouncing from 80-120 like a kid on a trampoline. So I advised it looked like a gauge malfunction as the actual temperature couldn't fluctuate that quickly and to drive home steadily. Then a few mins later she called from the hard shoulder as it felt sluggish and was limited to 60mph. I advised driving on and she managed a few more miles until on an uphill slip to join the A1(M) the stop message came up and it felt too sluggish to safely join a motorway for the last 5mls home.

So I nipped out and rechecked under the bonnet with no visible issues... gave her my car and drove the CLK home. By the time I was back limp-home had restricted it to 3rd gear and under 40mph.

Anyone had anything like this where the suspicion is that the ECU is getting an over-stated temperature readings causing an associated limp-home.

 

[Droverunner]

Just a hopeful update for anyone interested. Car has been standing since yesterday and I've just been out to it with our home outside temp gauge showing 26deg. Switching on the ign without starting the coolant gauge goes straight to 100deg and the iCarsoft shows similar at 102.6deg. Last pic as a comparison my unstarted Viano correctly shows the same coolant temp as the ambient temp.

So hopefully just the CLK coolant sensor in the top of the thermostat housing to replace. I'll nip up to Mercedes in a moment to buy/order.

 

[Droverunner]

Final update. New coolant sensor from Mercedes only £15. Hidden at first then easy to swap. Instantly the new sensor showed ambient temp at rest and a test drive shows all is well.

In the end after dramatic symptoms an easy and cheap repair.

 

[daibevan]

Result.
So if you had gone to the main dealers it would have only cost £115.

 

[Droverunner]

Perhaps... but the last time I was near a main dealers it was £175/hr!

 

[daibevan]

I was going for half an hour, but it may be 1 h min & of course there's the diagnostic charge.

 

[Droverunner]

You never know what thought process they would have used to arrive at a repair solution and how much their thinking time might have cost. It seems very rare that a dealer job is under an hour labour and just one part for peanuts.

If this car had suffered this issue a long way from home and got towed into a garage approved by a recovery provider I hate to think what they might have come up with as the investigation and repair needed. It was so utterly dreadful to drive on full limp-home you'd almost have believed any place that told you it needed a new engine.

 

[daibevan]

It happened to me once on the dualed section of the A38. 30mph, less up hill with lorries doing 70+ zooming up behind me. Brown trou time. I must get me one of those scanners. Used once in anger pays for itself.

 

[M80]

I've driven 100 miles or so on limp, but I knew from my onboard Torque app that the EGR had given up.
That was returning from London as we changed from the M25 onto the M1. As that was the 642 Viano, while it took a bit longer to accelerate it wasn't v noticeable. The only time it was 'sluggish' was back in Derbyshire when we encountered hills again.

For your temperature issue had you taken it in to a main dealer of self importance I suggest they would carry out,
a road test to confirm fluctuating temperatures, maybe a 1/2 hour.
Plug in diagnostics, is that often £150 now?
Replace the whole stat, and if they don't have one in stock return for the van after a couple of days, depending how busy they are.
An hours extra labour.

Well done for your own resolution technique, 'they' will have to get some other soon to be poor bugger.