I’m having an issue with my Discovery - the coolant temperature gauge goes up and up and even into the red if it’s been sitting for a bit, like in traffic. I’ve made sure to pull over anytime it’s gone up that high, which isn’t always easy - freeways, one-lane mountain highways, traffic lights at busy intersections, etc.

I’ve refilled the coolant at the expansion tank and found that it was low, but after refilling, it seems to have bled off excess coolant at the expansion tank - there’s a short hose that seems to be for that purpose. Is this correct and how things should be? Once after parking, the car seemed to have spilled out coolant in a way that it caused it to steam up maybe after spilling onto something that was hot beneath it. I’d also noticed that the expansion tank seemed to have another port underneath it that wasn’t connected anywhere - is that normal?

I’m wondering how I can test if the fan is working since it seems that it doesn’t always run. I’m also wondering about bleeding air out of the system and doing a full flush, if necessary. It’s there a procedure that will allow me to bleed just the air (if that’s the problem) without draining all of the coolant?

I’d replaced the thermostat and expansion tank in my 1991 Range Rover. Could it be that I’m looking at the same issues here? I’ve already replaced the thermostat, radiator and most of the hoses in this D2 a few years ago. I can’t remember, but I think the coolant gauge used to reach operating temperature (mid-level) in under a minute when I’d replaced the thermostat and now it takes a few minutes. It’s a bit colder where I am now, but not by much. I can’t remember if I installed a regular version or a warm weather version thermostat.

Is there anything more serious I should look at, like the water pump? I can check if the serpentine belt is pulling, but I wouldn’t know how to know if the pump is working properly.

I just flushed and changed the engine oil and didn’t notice anything milky about the used oil, but my eye isn’t trained enough to be 100% sure about anything I might have gathered there.

 

If it only runs hot idling and not on the highway, it is likely the fan clutch. Are you monitoring the temperature with an OBD device?

 

I’ll connect my OBD device and leave it connected while driving - good idea. What temperature should I watch out for?

Today as I was getting close to the on-ramp, it was getting hot (or showing that it was getting hot) so I pulled over at a gas station instead of getting on the freeway.

Do you know how I’d check to see if the fan is working or anything than be done to get it moving again? Should the fan be running at all times the engine is running?

EDIT: Fan is turning - could it still be the problem?

Serpentine belt appears to be OK, although I wouldn’t know if there’s still a water pump issue.

Added a bit more coolant for now. As I added it, some came out from the second hose on the expansion tank. Photo:

 

When your engine is stone cold, like first thing in the morning, open the bleed screw and look for the level of the coolant. If you see any air at all you have found your air pocket which migrated to the the highest point in the system. Add coolant directly into the bleed hole until it is topped off. Put the screw back in and go for a drive. Check again the next few mornings for more bubbles migrating up, fill as needed until you no longer need to.

This will work unless you have leaks.

 

Thank you - the bleed screw is right in front of the alternator, right?

Just to make sure I understand this procedure: I’ll leave the car sitting overnight and in the morning, open the bleed screw and look in to see if it’s not completely full of coolant? If there’s air, I’ll add coolant from the bleed screw hole until it’s full, which I’ll gauge by watching the cold level in the expansion tank?

I might have a mix of different coolants in there. I’m trying to find the total capacity, which appeared to be about 13 quarts.

I also found a German-made coolant that’s supposedly the factory specified coolant, but it costs a lot and comes in 1.5qt bottles, which would make this quite expensive. I’ve seen that some owners use Dex Cool or compatible coolant. Is that a standard recommendation? Temperatures locally range from 25F to 100F (both extremes) - typically it’s around 45F-70F.

 

Yes, the bleed screw is at the T by the alternator in the upper radiator hoses... no need looking at the expansion tank... You'll want to make sure your level is good there, and if not add to the tank through its lid. That will not effect what you are doing with the bleed screw. If possible fill through the bleed hole until that is full then replace screw. That's it. No other level to look at. Other than drive it and check again the next morning looking for more bubbles to appear. You will know if it is full and needs no more.

Regarding the mix of coolants, These came with Dexcool. Dexcool reacts poorly with oxygen. That isn't a problem until you have air in the system... Regular green is fine but as you aren't sure whats in there, when you are ready to address that, drain and flush a few times and then add the coolant of your choice. You don't need any expensive magic juice. When you do flush your system, the way to refill is, once you have everything back together, raise the expansion tank up about one foot, open bleed screw, add coolant into expansion tank through its opening until a stead stream flows out the bleed screw hole... Place bleed screw into hole while coolant if flowing a clear bubble free stream. replace tank to its location. Run the vehicle and again check the level through the bleed screw once the engine is again all the way cold. top off as needed.

 

One of the first things you learn on this site is to always monitor your temps with something like a ultraguage they will beep at you at the desired temp you set it to
I wonder how hot your engine is getting when they needle is pegged. Your asking for big trouble

if it only happens at idle you could have a bad fan clutch or maybe even water pump
do you have heat at idle coming through the vents ? You should have a ton. If not your water pump is not circulating fast enough at idle.

 

As others have said, "normal" temps while cruising and temp spikes when idling indicates a problem with the fan clutch. I'm skeptical that your problem is air in the system, but I could be wrong.

To test the fan clutch, try spinning the fan by hand (with the engine off, of course). It should not spin freely. Some say it should feel as though it's being kept from spinning by peanut butter.

Also, the small line coming from the neck of the reservoir with the red arrow pointing to it in your pic is there to do just what you observed it doing.

 

I doubt there is just one problem here too.

 

@neuropathy as @mln01 noted the pressure relief on your rad cap is working so that is great. Now for the bad news at idle even with a dead fan clutch and properly filled and bled cooling system you will not over -pressure or overheat.

You can buy a 25.00 bluetooth ODB reader on Amazon and the next get the Torque software for Android - free or Iphone 6.00
Set it up and monitor your actual engine temps - without these everything is literally a guess

Mine will idle for a half hour at 194 degrees without issue, I do however have a 180 deg thermostat.

So a few things to check
How much coolant are you losing - check the tank before you start in the am see what the level is, you should also get a hiss of pressure being released if you open the rad cap
Next top it up and bleed the system so you have a valid starting point
Try idling without moving - ideally after getting an ODB reader and torque, see how fast your engine temp rises it should be fairly gradual
While idling watch your expansion tank - you should see fluid movement pretty much in the area under the rad cap - if there is none it could be a water pump

You could have :

Air in the system
Bad fan clutch
failing water pump
Failing head gasket