Fluctuating temperature when towing in Td5

my Td5 is overheating under load when towing my small horse trailer. As soon as the engine revs drop the temp drops back down to normal again.

I do have a slight coolant leek but this is topped up and does not normally present a problem. The radiator is new as is the thermostat and there is no obvious sign of the coolant leek.

Any suggestions would be most welcome, especially if not too humiliating !

if you have a slight coolant leak then you might be getting an air lock, preventing the coolant from flowing properly. not entirely sure how TD5s (mine's a 300tdi) work but when topping up via the expansion tank are you removing the bleed screw from the top hose?

Does the engine feel hot when you open the bonnet and feel the water hoses. I had a similar problem on my 200 tdi. I changed the temperature sender unit which sorted the problem.

mojo247 said:

if you have a slight coolant leak then you might be getting an air lock, preventing the coolant from flowing properly. not entirely sure how TD5s (mine's a 300tdi) work but when topping up via the expansion tank are you removing the bleed screw from the top hose?

Click to expand...

Many thanks for your kind reply and sorry to take so long getting back to you

I have not followed your suggestion yet but now that I have it I am going to do this immediately !

Regards

Alan

mikescuba said:

Does the engine feel hot when you open the bonnet and feel the water hoses. I had a similar problem on my 200 tdi. I changed the temperature sender unit which sorted the problem.

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Thanks for your thoughts. I have only just found your response and will have a look to see if this is likely to solve the problem

Thanks again Alan

If the leak is from a coolant hose clip I would suspect head gasket on its way especially as it happens when worked hard.

my guess is cylinder head. Especially if its a 10p engine with plastic dowels.
The head gasket is leaking causing your loss of water under normal conditions and under higher rpm and load the engine gasses are getting into the coolant and causing it to overheat.

However try everything else 1st. Top up the system and make sure you bleed it properly using the vents point on the top hose. Also change your expansion bottle cap as mine used to blow water out of the cap and I thought the head gasket was suspect.
if I fill mine total the recommended amount to it always dropped to about 2cm below the recommended line and states there forever, I know mine isn't alone in this

gazman said:

my guess is cylinder head. Especially if its a 10p engine with plastic dowels.
The head gasket is leaking causing your loss of water under normal conditions and under higher rpm and load the engine gasses are getting into the coolant and causing it to overheat.

However try everything else 1st. Top up the system and make sure you bleed it properly using the vents point on the top hose. Also change your expansion bottle cap as mine used to blow water out of the cap and I thought the head gasket was suspect.
if I fill mine total the recommended amount to it always dropped to about 2cm below the recommended line and states there forever, I know mine isn't alone in this

Click to expand...

Hello Gazman. I'm still having issues with overheating in my Td5 and, whilst I'm not yet fitted a new genuine LR thermostat, I have flushed the heater matrix both ways and no crap in there at all, I'm getting the thermostat changed on Thursday by my local garage.

I was out towing on Sunday and the engine overheated, when under power, but dropped down very quickly as soon as I " pulled back" on the power. The engine was running very well until after about 45mins driving, the engine cut out completely. I allowed the engine to cool for about an hour and refilled the cooling system with water, not ideal, but I was out in the Countryside and had little or no alternative.

I restarted the car and drove, without any issues for about half of one mile and the engine cut out again. I managed to get the horse and horse trailer towed home by my wife and arranged for a friend to tow me home.

I have been trying to work out in my mind, not the sharpest mechanical brain around, but can only think that, apart from loosing coolant, could the thermostat be "locked" in the closed position?

I only use the vehicle once or twice a week so it doesn't get the excercise it deserves. I have replaced the water reservoir cap, which I could blow through before it was replaced. I have flushed the system through with a garden hose and cold water. I removed the bleed screw on the upper most part of the coolant pipe, which is just back from the radiator. The radiator was new last year - aluminium BritPart, the thermostat was replaced at that time BritPart.

After flushing today, I got the engine "warm" but could only get the temp gauge of the blue sector. The top water pipes where hot, the inlet pipe to the heater matrix was warm/hot. The radiator was cold, except for the extreme right had side, looking from the front, which was slightly warm/hot, which I suspect was heat transference from the water pipe above the thermostat. When flushing the system, I took of the small rubber water pipe of the bottom left hand corner to make sure that the water was running through clear. Which it was.

The fan was turning the whole time that the engine was running and I'm not sure if this is correct. I had assumed that the fan would only cut in when the engine was hot. It's a standard Td5 setup and doesn't have an electric fan.

I'm hoping that your own experience might allow you to give me a view?

the td5 has what is known as a viscous fan. They turn all the time, best bet is Google it and read up on how they work.
Have you any obvious water leaks anywhere? water pump? hoses etc? if so start there. If not a pressure test at a garage or having the expansion bottle tested with a sniffer for exhaust gasses would be where I would start as it seems you've done most things as if it's the head gasket you could end up changing all sorts and be really out of pocket.

Thanks for your support Gazman. I think that I have found the source of a leak in my Td5. I say think, because I can see the drips on the ground but, until it's up on a ramp, I can't tell exactly where it's coming from. Looking from the front of the vehicle it's coming from somewhere on the left hand side, close to the engine block and midway between front and rear of the engine block.

I'm going to be taking it to the garage tomorrow and I'm hoping to see the car up on the ramp, so that we can find out exactly where the water is coming from. Until then I'm going to have to hope that it is not something serious. thanks for your help

If it's on the left as you're looking at the front of the car, that makes it the driver's side? If so it might be the fuel cooler, which can leak occasionally. That wouldn't necessarily make it overheat though. Try one of those kits that let you test for traces of combustion gas in the coolant - they seem to be getting quite reasonably priced these days. Or get the garage to do it. It won't guarantee that the head gasket is in perfect condition, but at least you can rule out a major HGF if it comes up clear.

Yes Mr Brown, that's the drivers side. You say that a leak at the fuel cooler wouldn't necessarily cause overheating, but I'm assuming that any escaping coolant will, eventually cause overheating. Surly, it has to.

I'm still thinking that there are two issues; 1, the thermostat is locked in the closed position. Like most Td5 defender engines it runs cool/cold. I only use it once a week, on average. That trip takes about 25 mins each way with an 75 min stop and another 25mins return journey. My thoughts are that because of the very slow cool/cold warm up of the engine, the thermostat could be in the closed position for a few weeks or even months. This, in its self might cause the thermostat to malfunction?

2, the coolant leak will inevitably depleat the volume of fluid. The question then becomes one of, if the thermostat is locked in closed position, can the coolant escape from the area which you suggest. - by the fuel cooler?

I don't know if the pressure in the system is present on both sides of the thermostat. Having said that, I did read that there are two inlet junctions on top of the thermostat, one sends coolant to the engine, when opened, but the second directs a flow of coolant past the closed thermostat irrespective of what position the thermostat is in. If that's correct, the coolant that bypasses the thermostat must be under pressure because it is being circulated by the same pump.

You are a clear thinker and cleaver fellow- what do you think?

Really appreciate your help and view.

Ah, you're very kind, sir.

Yes, if you let the fluid get very low it'll overheat, but if it's just a few drops and the level is still visible in your plastic header tank it won't cause overheating all by itself. Yes, whatever the position of the thermostat you could get a drip out of the fuel cooler because it is below the header tank level. The thermostat is a peculiar thing on the TD5 - a kind of Y shaped plastic device with a tube on each arm. You could try taking it off the car and boiling it in a pan and see if it makes a difference as to which arms are 'open'. Or try a new one, as they are a weak point. But I'd be checking for combustion gas in the coolant next if it was mine.

Thanks again for your kind reply. I have a new LR thermostat which will go to the garage tomorrow to be fitted. When I get the current one back I will test it as you suggest, just for my own peace of mind. It's only about 10 months old, but not a genuine LR part. It was about half the price of the new LR unit, but that's history and I can't do anything about that.

I'm not certain that my local mechanic will have anything to check the combustion gasses in the coolant, but I might be doing him a great disservice. He's a really good, old school Polish mechanic who will mend things, if at all possible, rather than just replacing with a new component.

I'll let you know know how it goes tomorrow or Friday. If it's bad news, then I will revert to being "a man of few words "!

mojo247 said:

if you have a slight coolant leak then you might be getting an air lock, preventing the coolant from flowing properly. not entirely sure how TD5s (mine's a 300tdi) work but when topping up via the expansion tank are you removing the bleed screw from the top hose?

Click to expand...

Hello Mr Mojo. I had the car down at my local garage this morning and the mechanic found the leak within seconds. He put it up on the ramp and it turned out to be a coolant pipe which looks like it comes from the radiator but was rubbing against the chassis. Big relief, many said that it was almost certainly the head gasket

Alan Crossley said:

Thanks again for your kind reply. I have a new LR thermostat which will go to the garage tomorrow to be fitted. When I get the current one back I will test it as you suggest, just for my own peace of mind. It's only about 10 months old, but not a genuine LR part. It was about half the price of the new LR unit, but that's history and I can't do anything about that.

I'm not certain that my local mechanic will have anything to check the combustion gasses in the coolant, but I might be doing him a great disservice. He's a really good, old school Polish mechanic who will mend things, if at all possible, rather than just replacing with a new component.

I'll let you know know how it goes tomorrow or Friday. If it's bad news, then I will revert to being "a man of few words "!

Click to expand...

Up on the ramp and the mechanic found the leak within 30 seconds. Typical of the man, I said that I would order a new replacement, but not for Joe! The coolant pipe was rubbing up against part of the suspension. He's going to cut the rubbed & broken rubber and put an insert between and a couple of clips to seal.

The new thermostat will go in later today and hopefully that will be the end of my coolant issues for a while!

mojo247 said:

if you have a slight coolant leak then you might be getting an air lock, preventing the coolant from flowing properly. not entirely sure how TD5s (mine's a 300tdi) work but when topping up via the expansion tank are you removing the bleed screw from the top hose?

Click to expand...

Took it to my local Polish mechanic today, put it up on the ramp and found the leak within 30 seconds. A smallish coolant pipe had been rubbing up against the chassis and had gone through to the coolant side of the pipe! So, with a little bit of luck, it will be an inexpensive fix just the sort I love

The ongoing sarga: new LR thermostat fitted, two damaged coolant pipes repaired, tested and now good. About half mile from garage and same from home, engine cut out and would not restart. Towed home by a neighbor behind his Lamborgini (tractor not car) and now it's sat half way up the front drive, looking very sad.

Someone suggested that the problem could be the injector washers but, as yet, has not come back to me to explain his/her thought process

Any other ideas will be welcome

Alan Crossley said:

The ongoing sarga: new LR thermostat fitted, two damaged coolant pipes repaired, tested and now good. About half mile from garage and same from home, engine cut out and would not restart. Towed home by a neighbor behind his Lamborgini (tractor not car) and now it's sat half way up the front drive, looking very sad.

Someone suggested that the problem could be the injector washers but, as yet, has not come back to me to explain his/her thought process

Any other ideas will be welcome

Click to expand...

When you say cut out do you mean like the ignition was turned off or spluttered and died?

Also does it turn over? Any clicking? Warning lights on dash?