Defender 300tdi overheating issues

I'm looking for some advice from more experienced owners please.
I took the LR on a longish trip of about 100miles to the south coast. Much was on dual carriageway at about 60-65mph. All was well temperature wise for about 50miles, then the gauge went right over into the red. Stopped, carefully checked water, waited for some time, then restarted, but kept the speed lower. I had the heater on, so was dumping heat into the cabin. Made a further 10miles before I had to stop again, this time calling out family rescue. Engine cooled much while waiting, and could drive a further 30miles on single carriageway, reduced speed, before the temp needle headed into red. Got some tools and returned to it, suspecting the thermostat, I removed that and carefully drove the remaining 20miles.

Old stat didn't work as suspected and was replaced. Return journey was similar - overheating issues again, so removed thermostat and retraced route at lower speed, temps at 11.30 as usual. I now suspected water pump and/or blocked rad.

Water pump and p-gasket replaced, block flushed through, rad flushed through (should there be some resistance? I had to seal the hose pipe as much as I could to get water through), all showing clear water.

Rad was reluctant to fill from header tank on rebuild which I thought was strange - how much resistance does a rad give to water? It was replaced 10th May 2017 , so should be in pretty good shape having covered 6500 miles. Top of stat housing and rad bleed points used, as much air as I can removed.

On driving today, bottom hose nice and toasty, top hose not, temps still reading 11.30. Turned heater off, continued test drive back home to find top hose now 'working'.

My question is, is this normal for a LR, I would have thought the rad would have filled up easily from header tank. If the rad is blocked, how would I got about unblocking it without wrecking it? I'm trying to tick off all the cheaper solutions first, before looking at the price of a new rad (or even head gasket...!)

Thanks for reading through all of this and any ideas you can put forward.

Since you're doing cheap first, I'd suggest the temp sender and gauge go in the bin, and fit a proper temp gauge - Durite would be my call. Then you will know the actual temperature of the coolant.....

Did you work out what has caused the gauge to go "right over into the red" ? Need any coolant?

It sounds like your rad is an issue - when was the antifreeze last changed ? Corrosion inhibitors in same are essential to keep the rad clear of crud...

If it's a proper brass ends rad - I.E. an OEM one, then get it recored - don't fit a new one made from chinese-ium.

Which water pump have you fitted, IME only Quinton Hazell = OEM metal impeller are any good - again chinese-ium stuff is carp.

I'd also suggest a search, as this has been done to death - and the common issues well covered

( though whether the search is working today is anyones guess )

Thanks BFG
Coolant wasn't lost at any stage, even when it went into the red. Coolant last changed 10th May 2017, rad is a proper brass-ended one as like you I didn't fancy chinese plastic floating about. Other than that I've drawn a blank as to the underlying cause, but leaning towards your thoughts of rad problem.
Water pump is KWE, supplied by motor parts shop. It has metal impeller though which I was pleased to see.
I've searched lots on google and beginning to think the rad is stuffed, although no gunge came out when it was drained. Is there mileage in using diet coke, kettle or dishwsaher descaler to clean it out? anyone tried this and what are your results?

florncakes said:

Coolant wasn't lost at any stage,

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So, .... did it get hot then? serious question - donkeys year ago i got brought a Spitfire (Triumph, not Supermarine!) with a "cooling problem" - it was not dissimilar to what you describe - would drive for a while, then the gauge would go ballistic ...... they had changed everything ... rad, pump, hoses and even the viscous coupling on the fan .... now, Spits were known for overheating ( P*ss poor BL QC , often caused by casting flash in the cooling system obstructing the flow ) ... but I was assured this was all good ... took it for a drive and sure enough ... gauge in the red - open the bonnet and it just wasn't that hot ...... changed the gauge sender and the problem went away

Hence my first suggestion

De-scaler will work, but I'd want to know if the thing really is as hot as it claims to be, first

That's got me thinking now, I did put my hand on the rad and noticed it really wasn't that hot at all. I'd expect to have to flinch away from it at least, with the needle in the red.
Further searching on tinterweb has me thinking about the state of earthing connections - something to check on tomorrow, then replace sender and gauge.
Thanks for your input BFG - very useful.

florncakes said:

That's got me thinking now, I did put my hand on the rad and noticed it really wasn't that hot at all. I'd expect to have to flinch away from it at least, with the needle in the red.
Further searching on tinterweb has me thinking about the state of earthing connections - something to check on tomorrow, then replace sender and gauge.
Thanks for your input BFG - very useful.

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It sounds more and more like the bl@@dy gauge

Earthing is a good call - any electrical weirdness on anything LR .... and it always prudent to check the earths - have you got RAVE ? - might not apply completely to your vehicle - but is full of fine info and most of the earthing points are more or less in the same place they always were, or thereabouts

have a nosy here for a durite capillary gauge

www.ebay.co.uk/itm/322993477122

( non tracking link too )

Be wary of Durite water temperature gauges. I read many positive reviews about them and decided to replace all my gauges with durite. All worked a treat with the exeption of the water temperature gauge. As soon as a current was fed to it, the needle jumped up to 50 deg. A new sender unit did not help matters so I gave up and bought another complete gauge and sender and got the same result. Complaints to Durite fell on deaf ears.

reiny said:

Be wary of Durite water temperature gauges. I read many positive reviews about them and decided to replace all my gauges with durite. All worked a treat with the exeption of the water temperature gauge. As soon as a current was fed to it, the needle jumped up to 50 deg. A new sender unit did not help matters so I gave up and bought another complete gauge and sender and got the same result. Complaints to Durite fell on deaf ears.

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Sorry to hear that, but it's one of the reasons I recommended the capillary gauge, not an electrical one...

IME, Durite have always been very helpful, and I am concerned they ignored your issues..

I hear what you are saying about the gauges but this also rings alarm bells, the rad should flow water through it freely?

florncakes said:

rad flushed through (should there be some resistance? I had to seal the hose pipe as much as I could to get water through)

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Disco1BFG said:

Sorry to hear that, but it's one of the reasons I recommended the capillary gauge, not an electrical one...

IME, Durite have always been very helpful, and I am concerned they ignored your issues..

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i agree mechanical reading is better to determine if its an electrical issue as we need to compare data its classed as a 2nd opinion

electrolysis can also be an issiue use a volt meter is there a voltage in your coolant system when engine is running ..if your radiator isnt free flowing on its own (disconnected from the engine ) ?
then you have found the issue as your radaitor should be free flow on its own

in a man shed you will normally find a sniff test kit ..this test kit takes aproxx 30 seconds to rule out curtain areas i have also seen head bolts heads etc fail in many ways specially on charged engines

i hope you have not caused more damage .as the 300 tdi will keep going till seizure

The rad should flow water easily, not need to be forced through by sealing up the hose.

Have you tried reverse flushing it?

Infared temp guns can easily check temperature.

dstainton said:

Infared temp guns can easily check temperature.

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alternatively, if you do not allow for the emissivity plus cone of the reading area against the distance from part , they can give very bad information. Only of use if you have validated it against a contact surface probe measurement. Otherwise treat a measurement from an IR temp gun as suspicious.

Cheers

Another new thermostat (checked it opens indoors), descaled radiator with harpic tablet (!) overnight, new sender installed.
Runs, warms up. Will give it a more robust road test tomorrow now I've identified and repaired failed headlight switch!!
Thank you for all advice - fingers crossed it works!