FFS! Overheating, let's flog it again
 

I've spent some hours searching old posts but can't seem to find anything to answer my problem.

96 XJ 4.0P. Always maintained to the best of my knowledge, no leaks, no knocks no squeeks.

When I first bought my XJ 5 years ago, it was running fine. I took it up to Stockton (from Sydney) and apart from getting up to the 3/4 mark on the sand, everything else seemed to operate normally. A couple years later the stock radiator gave way at the tank seem.

So i've been running an Adrad two core full copper radiator since three summers ago. Installed just after Summer, together with new fan clutch and thermostat.....so the cooling system ran ok till the following summer, when it needed a new water pump due to weep hole leakage. It would generally run ok, 95-105 depending on conditions.

Two summers ago, it showed signs of running less efficiently....got up to 112degs on a hot day in the traffic with aircon running and was running consistently warmer than usual, so I did an eletric thermo fan conversion. That ran ok that summer and up until the next summer when it started struggling again to stay cool on very hot days in traffic (would run up to 110deg regulalry in stop/start traffic)(but always cool down again once moving). So I thought I'd upgrade from a 14" thermo to a 16" thermo and also installed an 82deg thermostat. Again, it ran better after that (made the change towards the end of summer) until this past summer.

On our way up to Umina from Sydney for our summer camp (ie fully loaded cargo bay, roof and trailer + 4 bodies) she ran hot on the freeway, got up to 115-120deg (into the red) on the hills and sat on 105ish otherwise. I attributed it to the load and didn't worry about it as she only got that hot on the hills and cooled back to the on the flats. On our way back home was worse, much worse......it was a 32deg day and she got up to 127 at the top of a hill before I pulled over...and watched the scangauge continue up to 134 with the engine off before it cooled back down. By this time, coolant had boiled, steamed and escaping through the radiator cap. I think this is also the point at which the radiator sprung a leak...right where a couple of the core channels meet the tank. We had to stop another 4 times on the way home turning a nice 1hr20min drive into a stinking 5 hour drive.

Since that day, she's been running hotter than usual. During normal driving in mild conditions, she slowly gets hotter and hotter.

I've had the rad repaired and the repairer (who I have trust issues with) said that all the water channels in the radiator are flowing...he claims he only took off the cool side tank to make the repair.

I've flushed the system with rad cleaner twice. Installed a new thermostat, water pump is 2yrs 50K kms old, radiator is 'supposed' to be ok. When I measure with an infrared thremometer, there's approx a 15-20 deg drop from the hot side tank to the cold side.....this seems fair, but I'm not sure what it's supposed to be. When I rev the motor with the radiator cap off, I see the coolant being sucked down to indicate the pump is working. I'm at a loss as to what the issue could be.

I've seen suggestions on other threads that there could be a blockage/restriction in the block itself....but I've never seen anything from anyone to say they did anything to unblock it. I'm starting to think that may be my problem, but have no idea how to approach unblocking it...short of pulling of the water pump and getting something in there.

Any other suggestions?

You have not mentioned transmission cooling.
Aircon going flat out doesnt help things. 32 not hot enough to need aircon.
You have a 20 year old car, who knows how many km its done, torque converter may not be locking up as well.

Yes, apologies, I have an after market transmission cooler fitted in place of the standard one. It''s set up in front of the main fan. This was installed two summers ago and did not make any difference to my observed operating temps.

She has 203K Kms on the clock

All the temps I have mentioned were always WITH air con running....except on the way to and from Umina where things got critical.

Torque converter locks up fine.....and transmission is also fine.

Loosing any coolant?

Ive had two XJs never a real overheating problem.Last one I put in a Repco 16 inch electric fan.After 2 damaged radiators worked out that the blades were distorting when vehicle got hot, as fan pulling very hot air through radiator.In one case blade distorted so much it hit shroud and destroyed the radiator.In other words they are crap.I then went to a Davies Craig 16 inch ,they have composite blades to stop distortion no more problems .Also check the fan blade is the correct way around it can be used as a pusher and puller.I would also put correct temp thermostat back in ,the ECU monitors temps etc with regard to fuel supply.

Not losing coolant. No oil in it. No coolant in my oil.
No issues with fan, its definitely pulling and the blades don't touch anything.

FYI, when you pulled over to let it cool down you should have left the motor running. The heat in the block will very quickly boil the stationary water and squirt all your coolant out the overflow.

I can only suggest a HD radiator. It will help but may not be your problem.