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Jabberwocky

Member Since: 27 Oct 2021
Location: Luxembourg
Posts: 234

Help with cooling system needed

Ok so I replaced the header tank and then refilled and blead the system. Took it out for a test drive and it came up to temp as per normal. I had plugged in my Nanocom for the first time on the test drive to see what temps it was running at, temps climbed steadily, then into the 90s then reached 100 and settled down, a bit hot for my liking considering it was only about 10* and I was on flat ground doing 55 mph, temp gauge never budged passed its normal position but I cut the drive short and went home.

When I got back I had a look at things, I’d lost no fluid, the aircon fan had not come on to aid cooling, top hose was hot, as was every other hose apart from the bottom hose which was cold. The top of the radiator was hot across its whole length but below about 3 inches it was cold.

The radiator and thermostat have no more than 1200 miles of use, the heater in the cab runs hot.

What am I missing?

Assuming the thermostat opens as it should, shouldn’t the radiator be hot all over?

Presumably the thermostat opens just before the gauge reaches its usual position so it can’t be that I hadn’t run it long enough to open the thermostat, can it?

Could the Nanocom be reading way too high? But that wouldn’t explain the coldness of the radiator

My plan is to reblead the system and go for another drive, but I’d appreciate any input anyone with more knowledge has for me.

19th Mar 2025 8:35pm

landy andy

Member Since: 15 Feb 2009
Location: Ware, Herts
Posts: 5842

2006 Defender 110 Td5 USW Zermatt Silver

So your problem is that it was at 100 centigrade ?

Everything else is ok.

If that is the case I would not be overly concerned. I’d expect it to be in the 90 degree range anyway
Thermostat starts to open ar 85 and fully open about 90. So by the time the thermostat opens closes it’s going to be a bit higher than that. A diesel engine wants to be at least 90

Take it on a good run and see how it goes.

20th Mar 2025 5:50am

jst

Member Since: 14 Jan 2008
Location: Taunton
Posts: 8199

2011 Defender 110 Puma 2.4 USW Stornoway Grey

Does nanocom take head temps of hose temp? The former I expect. Cheers

James
110 2010 XS Utility
130 2011 M57 bespoke Camper
90 2010 Hardtop
90 M57 1988 Hardtop

20th Mar 2025 6:27am

Jabberwocky

Member Since: 27 Oct 2021
Location: Luxembourg
Posts: 234

landy andy wrote:
So your problem is that it was at 100 centigrade ?

Everything else is ok.

If that is the case I would not be overly concerned. I’d expect it to be in the 90 degrees bit of reading range anyway
Thermostat starts to open ar 85 and fully open about 90. So by the time the thermostat opens closes it’s going to be a bit higher than that. A diesel engine wants to be at least 90

Take it on a good run and see how it goes.

Yes the 100* and the Nanocom doing an overheating alarm freaked me out, having done a bit of reading I think I stopped the test drive too early, I’ll take it out again and see what happens, thanks for the reply.

20th Mar 2025 9:11am

MadTom

Member Since: 10 Sep 2013
Location: Olomouc
Posts: 645

With Nanocom look also at other temperatures - at least fuel is cooled by watter and has separate temperature sensor. And don't just look for actual values, but check, it there is rise or fall acconring to car/engine run. "Drobek" = The Small One - Discovery 2, "Blufínek" = The Blue Thing - Defender 130, and for me at least Ford Mondeo

20th Mar 2025 10:13am

landy andy

Member Since: 15 Feb 2009
Location: Ware, Herts
Posts: 5842

Jabberwocky wrote:
landy andy wrote:
So your problem is that it was at 100 centigrade ?

Everything else is ok.

If that is the case I would not be overly concerned. I’d expect it to be in the 90 degrees bit of reading range anyway
Thermostat starts to open ar 85 and fully open about 90. So by the time the thermostat opens closes it’s going to be a bit higher than that. A diesel engine wants to be at least 90

Take it on a good run and see how it goes.

Yes the 100* and the Nanocom doing an overheating alarm freaked me out, having done a bit of reading I think I stopped the test drive too early, I’ll take it out again and see what happens, thanks for the reply.

Had a check of mine this morning. 10c at start. Drove 4 gentle miles to where I was working, never went above 40mph, arrived with temp at 95c.

I’ve had the nano temp scare before now you mention it, and think you can alter the threshold. But 100 isn’t unusual.

20th Mar 2025 3:53pm

Jabberwocky

Member Since: 27 Oct 2021
Location: Luxembourg
Posts: 234

Yeah having done a bit of reading the temps don’t seem as scarily high as I’d thought. Any further testing was put on hold when I discovered a fuel leak, new pressure regulator ordered🙄 another job to do.

I did notice the header tank cap wasn’t as tight as it could have been so maybe the system wasn’t pressurising as it should be.

20th Mar 2025 8:55pm

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