Help TD4 overheated today towing caravan

Towing our caravan today with my 2005 TD4 HSE Auto to the Peak District and the sat-nav took us along a B road with quite a long steep hill. I took it fairly easy to get up the hill, didn't floor the throttle, just crawled up at around 30mph. At the top of the hill, temp needle went off the scale and we had steam etc.

I pulled over and switched off the engine immediately, antifreeze mix boiled and had blown out of the expansion tank cap (a new cap fitted just a week ago). Let the engine cool down and managed to get some water to top the engine back up. It took about 2.5 litres to get back to the max level mark on the tank.

After about 30 mins, restarted the engine and all seemed ok so towed the last 10 miles to the caravan site. At the site, the level had dropped again below the min mark but the ex tank hadn't emptied. Figured this could be down air in the system finding its way out after refilling.

Topped the coolant back up and went for a drive without the caravan and all seems fine.

Fans work ok with the ac on but don't come on when the engine is just ticking over and the temp gauge doesn't go over half way.

Thinking maybe the fans didn't come on when they should have done. I understand the fans are ECU controlled so there must be a temp sensor in the block?

Anyone had experience of this happening, is there a sensor that can be replaced so I can rule this out? As far as I can tell, no coolant is leaking from anywhere.

Towing the caravan home on Monday and thinking I might just get us recovered rather than risking it happening again, and get it into a garage to be checked. Didn't have any engine management lights come on.

Sounds like you had / have an air-lock.

When did you last change the coolant?

Why did you need a new cap?

How many times did you check the bleed-screw?

It took me over a week of daily bleeding to get all the air out after a coolant change.

Thanks for your quick reply

The coolant was changed about 8 months ago as part of a service by an indy LR specialist. Over the last 3 or so months, i've noticed the coolant level dropping in the expansion tank just 1/2 an inch or so approx every tankful. Read on here that one cause could be a weak cap so I changed it. Have looked all over for other signs of leaking and couldn't find anything.
Changing the cap seemed to cure the mysterious small loss of coolant i've been getting recently.

Up until today, the gauge hasn't ever gone over half way, towing or not. It was a very long steep hill though which brought this on.

What was your procedure for bleeding? I can see there is a bleed screw on the right hand side of the engine bay. Do I just run the engine and open this until steady coolant comes out?

Se7en Stars said:

What was your procedure for bleeding? I can see there is a bleed screw on the right hand side of the engine bay. Do I just run the engine and open this until steady coolant comes out?

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Initially yes - but subsequent checking / bleeding is best done when you first start in the morning with the engine cold.

The first time I bled it after changing the coolant I got lots of air, but for several days more I just got a short phistt of air - but it was enough to stop the heater reaching maximum.

Only open the screw a couple of turns (a 1p coin fits well - no screw-driver needed) beware taking the screw right out as the little beggars have a habit of jumping out of your fingers and disappearing into 'never-never land' down the back of the engine.

My auto pulls a 2-tonne trailer on occasion and I agree that the gauge never goes above half.

If you get no joy with the bleeding fix - I would then be looking for a fan / temp sensor fault.

I've had the exact same event on my 1.8 - was going up a hill though not towing and the needle went pow. The fans kicked in like crazy so I stopped and it cooled down. Not had a peep out of it since. Though I've changed the inlet manifold gasket, expansion tank and cap. That solved my coolant drop trouble.

So yes, sounds like an air lock. I bleed after short journeys periodically - almost always a small amount of air to come out but it sounds better after each time.

Will.

Se7en Stars said:

I pulled over and switched off the engine immediately, antifreeze mix boiled and had blown out of the expansion tank cap

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were the fans running full speed when you pulled over?

I had the same problem, fine under normal conditions but stick the caravan on the back and it would over heat, so i bit the bullet and went for the thermostat and water pump. Bingo !! water pump impeller was lose on the drive shaft. so new pump and stat and every thing is fine now, even gets warm in the cabin now

Chaser said:

were the fans running full speed when you pulled over?

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No idea, didn't think to check. Just wanted to stop the engine asap before any damage was done.

There could be a fan control module fault, if it's that hot the fans should be on and continue to run even after switching off.

The gauge and the ecm/fan control share the same coolant temp sensor so if the gauge is behaving normally then assume the sensor is ok.

Towed the caravan home today and the car didn't miss a beat. We drove a different way home but there were still some pretty steep hills to climb. I was watching the temp gauge a lot more than I normally would and it never moved from just below half way.
At the top of one of the hills there was a layby so I pulled in and lifted the bonnet, the fans were running and controlling on/off
The only thing i've done then prior to returning home was to bleed the cooling system as described above and also disconnect the battery for a minute then reconnect (now where's that damn radio code) just in case it was a electrical/ecu gremlin.
I think then, the water pump is fine and the thermostat too, no reason to suspect them as faulty after today.

Next caravan holiday in two weeks. Fingers crossed it'll be ok.

when bleeding air out of the system you should have the cabin heater setings on hot hope this helps

teddywood1 said:

when bleeding air out of the system you should have the cabin heater setings on hot hope this helps

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makes no difference on a Td4.....