Overheating problem a long way from home
 

Have just arrived in Portugal having towed my 1420kg caravan with my Cdti Auto remapped 160.
Ran superbly until I came to a very long steep climb in Spain 1400 mtrs over 3/4kms (Hgv's crawling with hazards on) when temp gauge started to rise and engine went into limp mode, tried to keep revs as low as possible and made it with engine fading and picking up several times. Same thing happened after a further 200 kms, and on another nearly as steep climb temp went up but engine didn't fade. Completed rest of journey with no problems including many long steady climbs, gauge not moving from half way car pulling like a train.
Has anyone else experienced anything similar, is it the exceptional climbs with the load or could 2nd fan speed not be kicking in (it runs when a/c is switched on), is it possible to check it? I am sure when I had the remap not long back the fan was checked out ok albeit still with the original silver resistor.
I have a bit of time before the journey home and wonder whether I should be doing anything to give me 'peace of mind'. This is the first time I have towed such a long distance, up until this issue I have never had a temperature problem. Any thoughts would be most welcome.

When an engine works hard it will get hotter than usual, including the diesel. How hot will depend to a large extent on the integrity of the cooling system. The radiator fan must work as designed to keep the engine within normal temperature limits. On the diesel, the low speed should trip on at 105C or so. Since you have the later 2-speed fan, the slow speed resistor should be checked because they're prone to failure. This causes loss of fan cooling until the engine's much hotter. The resistor/low speed can be checked by running the so-called Demist test.

With a cool engine, turn the ignition on and press the Demist button. This effectively invokes the aircon system which requires the slow speed fan. It should start immediately and run continuously until Demist is pressed again (off). If the fan doesn't start immediately, then the resistor has failed. If you repeat the test with the engine on tick-over, the high speed fan will eventually start up and pulse on and off every 10-30 seconds. This is the emergency cooling which will also be tripped on if/when the engine approaches 120C. This also assumes an operational aircon system.

A replacement resistor should be fitted asap, though I realise that's easier said than done in the circumstances. As an emergency measure the failed resistor could be cut out and replaced using heavy gauge wire and good cable connectors. This will give high speed cooling instead of low speed, but is better than nothing. I'd also suggest knowing how to run the trip screen diagnostic mode so you can display the actual running temperature. The standard gauge is of little use to you.

The fan system is permanently live, so any such work must be done with the 80amp fuse removed in the engine bay fuse box or with the battery disconnected.

TC

I back up doing exactly as T-Cut says.

Thanks T-Cut
I have done that and fan comes straight on, also goes on and off respectively if I toggle between Auto & Econ. Previously I did have the engine running for quite some time, probably with aircon on, fan ran similar speed to the above test, I tried to block off the grille to induce engine to heat up but temp gauge stayed steady on normal mid-point, no fan 2nd speed cycling. Presumably my resistor is ok but still not sure how to test to see whether speed 2 is working maybe leave engine running a bit higher than tickover for a while longer or wait till the weather gets hotter out here and go on a good solo run and then let it idle.

Given that since the two episodes of overheating I have driven probably 800 miles mainly on motorway pulling the van at speeds consistently around 60mph and at times higher up some fairly long uphill gradients pulling either up to 2000 rpm in 5th or to c2500 rpm in 4th without any problem. Maybe I was just too heavy right footed on the steep climbs!

Would the auto box put the engine into limp mode if the ATF was overheating, apparently the diesels have a cooling fan assembly for the ATF.

Diesel 2 speed silver resistor fan
 

Hello Tony. Let's try to work out what's going on.

First of all, for a diesel engine temperature gauge to rise above 'normal' is a very serious matter. It indicates that the engine is seriosuly overheating. By the way, I think you mean that the automatic gearbox went into "limp mode" or, more accurately, "EP" mode which is Emergency Program.
Tony; when you activate the air conditioning the slow speed should run continuously. If the fan switches on and off rhythmically, that's the second (fast) speed. So what do you get: continuous running or switching on and off?


Actually, it's at 100°C. Come on T-Cut, you're an old hand on the forum, you should know this by now! :D

This is not advisable since the slow speed relay is not rated for the full motor current.
Forget speed 2 Tony. We need to be sure that the slow speed is working. Turn on the ignition with a cold engine and press the windscreen demist button. Is the radiator fan running? Also confirm that your air con. is in working order please.

I have no knowledge of an engine limp mode.

Simon

If the LP fuel pressure drops too low the ECM will put the engine into limp mode Simon.

Simple test to check is unplug the LP fuel pressure sensor - it sits on the top of the fuel filter.

Tony sorry if I'm stating the obvious, but have you checked the coolant level?

Mike; I could have sworn that someone told me that the diesel doesn't have a fuel filter. :shrug:

Simon

Ah well I did mention recently that it doesn't have a fuel filter in the tank. :D

It sits up front where it is nice and easy to access.

Thanks for all the input folks.
With a cold engine if I turn on ignition and press demist the rad fan starts running and goes off when |I switch off demist. Likewise the same happens when I switch on Auto on Aircon and fan goes off when I switch to econ.

The aircon is working ok

I trawled thru the workshop manual and could only find brief reference to engine safe /limp mode, which suggested that it is triggered if either water temp/ ATF or engine oil excessively overheat but no content that I could find to say what status the engine takes.

The first time the problem happened the engine power just gradually faded, I throttled right back, noticed then that the engine temp had risen, say 4mm on needle above norm half way point. Throttling back must have lightened engine load and power picked back up, temp rose and power faded again, did this about 6 times till got over the top and everything went back to normal.

Water, as well as cooling the engine, as far as I can ascertain also cools ATF so it could have been excessive coolant temp or ATF or both which triggered limp mode which led me to ponder on 2nd speed of fan not working to cool the water to cool the ATF etc.
As I said earlier I noted that HGV's going up this first climb were crawling with hazards on from fairly near the bottom so perhaps they were used to the route and knew the load it would place on engine cooling and maybe I should have been a bit easier.
If my fan is working correctly on both speeds then unless radiator airflow is restricted it was just the severity of the workload. I am fairly certain that airflow is ok but will have a look tomorrow, the aircon condenser sitting in front of the rad never struck me as ideal arrangement anyway. Thanks again for all your input.