I recently replaced the original functional thermostat due to a leak at the seam (just like the old plastic coolant pipes). First, I've done numerous parts replacements to the cooling circuit, including 4 pumps, pipes, hoses, radiators, etc. so I've familiar with the use of an air lift, bleeding, etc. Since the new thermostat, manifold temps have increased by 10-20 degrees ( now ranging from 221 to 233 F where previously it ranged from the 190s to 210 F) particularly during the first hour of the drive cycle and thermostat temps are lower, mostly siting at 70-90 degrees F. After multiple drive cycles or long stationary idling, thermostat temps increase and manifold temps decrease, as expected. This has been with warm, 80-90 degree ambient temps.

However, today was the first day ambient temp dipped to the low 50s and this time after about 10 minutes from a cold start, with thermostat temp staying in the 50-60 degree range, manifold temp started climbing rapidly to the high 230s and the cluster temp indicator started rising. I immediately turned on the heat and manifold temp dropped to the 2010s for a short time but then climbed up to the high 220's. Thermostat temp stayed very low. Later in the, temp readings normalised.

Thermostat does work (as with the previous one, if idling for expended periods, both temps level out at around 200 degrees. There's no air trapped.

So why have temps increased this way and why did it nearly over heat with cooler ambient temp?

 

Good morning.
As you know, you are at the high end according to the workshop manual.
Glad you are using a thermometer to read the temperatures and pinpointing different parts as opposed to relying on the ODBII sensors. (Clearly a geek like me)
This is perplexing. If temperatures are relatively constant at the thermostat, and climbing elsewhere… (you know what I’m going to say)
Ok, I’ll assume for a minute, despite my gut, that there is no air in the system. And no blockage in the multitudes (ridiculous design) of pipes. Then I’m only left with the coolant itself is inadequate in absorbing the heat from the engine OR the rate of coolant flow is inadequate for the job.

Am I missing something?
Cheers @jahummer

G.

 

I struggled earlier this year after replacing my thermostat.

I think there is air in your system. With the thermostat low in the system I think it is hard for the air to flush out there.

Try raising the coolant overflow tank and open the bleed screws at the front and rear of the engine until coolant comes out.

Other than that, keep doing what you are doing and monitoring the temps from sensor 1 that is on the cross over pipe at the rear of the engine like you are doing.

It took me many frustrating cycles before the sensor 2 temps started to rise and sensor 1 decline and then you know it is where it needs to be.

 

Ive had my 2016 LR4 for over a year now. The warmer the temps the cooler the engine temp. For example; hot summer days 80*F plus the engine temps read in the low 200s. The colder it gets 50* and below engine temps will be 220-226. I believe there is something the cooling system does with ambient temps. Ive watched it all year and the way it cools depending on the ambient temps is always consistent.