TD5 overheating

[martifers]

I have a white 90 King cab (Dewie), that has had a 2002+ disco TD5 transplant. On a trip to Dave Mac to pick up a beautifuly reconned front prop, Dewie overheated. I stopped and let him cool, checked coolant level which was fine, although did notice that the pipe from the thermostat to the bottom of the rad was not warm nor the bottom of the rad, while the top was very hot. Got home stopping a couple of times and by having a toastie cab. Immediatly thought was thermostat so changed for new, at the same time I flushed the rad and intercooler. The rad had a slight brown tint on flushing but soon ran clear. Seemed fine after, although did not give it a long run until a trip to Wales last weekend greenlaning. Was a great weekend with no problems untill the trip home on Sunday night where, again Dewie overheated. We stopped a few times, but in the end had to be recovered. Have since tested the thermostat that I took off originally to find it worked perfectly. I have also checked that the sender unit and temp gauge are functioning correctly, they are; showing half gauge at 90°C.

I am now stumped as to what to look at next! What could this be or have I missed something? I am not loosing any water and oil is clean so have personally ruled out headgasket, also being the later TD5 with the metal dowel gasket then I hope this would rule out head movement. Would a faulty rad or water pump coinside with Dewie's symptons? How can I check that the pump is working as it should? I can check that water is being sent through the system but I have no idea what sort of pressure is involved at tick over.

Any ideas, thoughts or theories would be appreciated.

[101sean]

Pump failure usually involves loss of water, don't hear of many TD5 ones packing up.

Does it only overheat when under load like on a fast motorway run? Could be either radiator badly scaled or the viscous coupling in the fan packing up (ie not locking up when hot)

Does the gauge suddenly jump to red or go up gradually? A sudden jump could be intermittant fault or short in the sender, try another, cheap and would eliminate it.

[bishbosh]

Flushing the radiator may not clear it. I would replace the radiator.

[martifers]

Pump failure usually involves loss of water, don't hear of many TD5 ones packing up.

Does it only overheat when under load like on a fast motorway run? Could be either radiator badly scaled or the viscous coupling in the fan packing up (ie not locking up when hot)

Does the gauge suddenly jump to red or go up gradually? A sudden jump could be intermittant fault or short in the sender, try another, cheap and would eliminate it.

Yes it only overheated when at load, as soon as I stop to idle the temp comes down pretty sharpish. The viscous fan has no wobble or play at rest and does rotate when running, how can I tell if the coupling has had it? The temp gauge goes up gradually, although I think I will take this oportunity to put in a more accurate gauge and sender. Glad to hear that maybe the pump can be crossed off the list.

[martifers]

Flushing the radiator may not clear it. I would replace the radiator.

I think I will, and see what happens. Cheers for the advise.

[martinhollings]

is the correct temp sender and guage set up used along with the ecu could be worth running with a nanocom conected to see the temp reading (if you can get your hands on one)and a td5 thurmostat has a valve in it that opens as the engine speed is increased but if the water pump is weak then it dont open

[martifers]

is the correct temp sender and guage set up used along with the ecu could be worth running with a nanocom conected to see the temp reading (if you can get your hands on one)and a td5 thurmostat has a valve in it that opens as the engine speed is increased but if the water pump is weak then it dont open

It is a stand a lone gauge and sender, not connected to the ecu one. Yes I will try and find someone friendly with a nanocom near by. Would be interesting to see how it compares. Mmmm... I didn't realise it was controlled through engine speed aswell, is this not just the extra pressure formed at higher revs, therefore the stat requires enough negative pressure produced by the pump to pull water through the rad. A weak pump not being able to draw the water through the rad would explain why the pipe below the thermostat does not get warm nor the bottom of rad. Knowing my luck it will probably be 'the water pump fins have corroded away, passed into the rad and blocked it' Which might explain the prob, and would require both to fix = ££! Think I'll replace the rad and while i'm at it take the water pump off and inspect. Cheers for the remarks, i'll see what happens and get back, have a slightly more urgent Series III Lighweight to fix first, found a lovely big crack in an intake valve on number 2 cyclinder this eve, had wondered why it wasn't runing quiet so smoothly recently lol

[Andrew Chua]

i've just had a situation like this.

here it goes. my temp gauge will sit at normal for quite awhile and then suddenly go to red and then back all the way donw to the blue and the power cuts out. still drivable. the moment you see this. you should immediately pull over. cut off the engine and hear the coolant bubble in the plastic bowl.

the problem :

i changed the water pump, thermostat and cleared out the radiator. my pump blades have totally disappeared. yes, the become the rust particles which gunk up the system. see the plastic bowl where you top up, you can't see the level of the coolant any more. it's a sign where the system is totally flooded with rust.

get all these fixed and if you have spare cash, change all the core plugs too. i had a core plug go like 3 weeks after this episode. large puddle under the truck when i parked up, so had to tow it to the garage. the plugs are cheap, but to get to them is going to cost you.

how to test the water pump before pulling everything apart? open the cover to the plastic bowl. run the engine, let it warm up. then floor the gas in one swift motion. does the water shoot out from the bowl? yes, pump is ok. no change the water pump. watch from a distance, if you can see the coolant movement when the gas is pressed. if slight, pump is on the way out. so as long you don't get the coolant shooting out, the pump is a suspect.

it's also good the check the thermostat if it's jammed open or closed. there's no easy way than to take it out to check.

[martifers]

Cheers Andrew for your thoughts. I think I may try that pump test. To update so far, have replaced the rad with a new one and whilst I was at it, I rechecked themostat and took off the water pump cover. The blades all seemed intact, although slightly discoloured. The pump was locked to the pully with only a little take up play, and the blades span when the engine was rotated. When we changed the rad, all seemed ok, it ran up to temperature, but as soon as I booted it, when under load, the guage shot up. I pulled over immediately to tick over and the gauge went down to normal within a minute or two. The pipe below the thermostat was not hot implying water was still not flowing through the radiator. When home, to make sure the rad was the path of least resistance for the coolent flow when the thermostat was open I restricted the pipe that runs from the top of the stat to the t junction joining the top of the radiator to the cylinder head. Then we let it warm up and took it for a drive, it worked perfectly, flowing through the radiator, with normal temp readings. What I don't understand is what could have caused the need to restrict the flow so that it flows as it should. The only addition to a normal TD5 cooling system is the addition of another temperature sender. This was done so by adding in a section of tube in which the sender unit was screwed, and thus reducing the cross section of the pipe slightly, could this slight reduction in csa be causing an increase in resistance thereby changing the flow balances in the system?

In the picture you can see the new section of pipe at the top with the temperature sensor and the grey pipe connector I used to squash the vertical pipe slightly.