Truck at shop right now for 2nd round of the same issue: engine temp cycles up and down, apparently independent of speed, ambient temp, AC on or off, or any other variable that I've noticed. Only once has it approached the red on the temp gauge, but I shut it down before breaking into the "bad bad bad" zone. I put in ~$2k for the same problem back in March and had no issues until last week - identical symptoms.

Questions:
1) I've not been able to find another thread with same issues described (generalized overheating threads all over, but my this feels rather specific and I've not been able to find a discussion that fits what I'm seeing) - has the legwork already been done elsewhere and I'm just missing it?
2) Does this feel like a specific problem with a specific set of fixes? Or is this just part of the generalized "it's an old Disco so quit your whining" category?
3) If anybody feels like they might have a clue here, what other info might be useful? I've not got access to the truck, but I've tried controlling the issue with engine speed, AC controls, and other random easy adjustments - nothing seems to have any affect (seems - I could be wrong here).
4) When I get call back form shop in next day or two, are there any questions I should ask or are there specific things that might be going overlooked?
5) What else should I be asking about or thinking about?

More details: Starting from cold, 1) engine comes to normal temperature readily and holds for 5-10 min, then 2) quickly (over a period of ~30-90 seconds) rises to upper end of "normal" range (per temp gauge) and holds at a "warmer than perfect" temperature for a few minutes, then 3) slowly drops back to normal temperature. Cycle repeats (normal temp, quickly rising to below red on temp gauge, holds at elevated temp, slowly drops to back to normal, holds at normal, quickly rises, etc).

Random background/info dump: Problem began in March. During short commute (~10 miles through city, ~20min) temp oscillated between "warm" (upper end of normal range) and "normal" but problem worsened over the course of a week to oscillating between "just below red" and "warmer than normal". Brought in for service at 57,600 miles. Identified coolant leak, replaced oil pump, water pump, thermostat, and gaskets (water pump, oil pan, timing cover). Problem solved. Last week, exact same symptoms appeared (59,500 miles) and truck is at shop currently for round 2. Check engine light has not come on other than "EVAP system leak" about a month ago. I reset light once and haven't seen since. It might be my imagination, but truck seems like it might be running slightly rough (if so, it's very mild and intermittent).

Vehicle: 2002 Discovery II - 60k miles - regular service, easy miles with 50/50 mix of daily commute through city and occasional highway trips.

 

I really can't intelligently comment as to the fluctuations, but my first response if maybe a cracked block. Have you felt the hoses to see if they are over pressurized/rock hard? Could be steam in the system from a crack.

Might help if you outline what you fixed for $2K the last time.

Also, you really, REALLY need to get an ultra gauge if you want to know whats going on temp wise. I have seen a gauge at middle point not budge until my Ultraguage was above 230.

good luck

 

Seen that behavior of fast temperature cyclic change when the coolant is wetting / not wetting intermittently the temperature sensor. Happens only at an exact point of lack of coolant. Sticky thermostat may have something to do.
When the sensor is not wet, thermometer shows hotter as steam is.
Check for reasons of coolant loss/level/air in it. It took since the last service for level to come down to reappear.

Perhaps you will like this :
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Who bled the air out of the cooling system and are you sure they did it correctly?

By what procedure was it bled?

There is a specific way and if you had this work done at a non LR specific shop then it might be that there is air still trapped in the system.