You should also know one of the proper bleed procedures, It isn't always enough just to top off the overflow tank. You could easily have air in your system if you didn't bleed correctly. The easiest way to find out is to open the bleed screw when the engine is stone cold. like first thing in the morning. if your coolant is not right to the top of the bleed screw hole, you have found air in the system. You can displace that air by trickling some coolant right into the bleed hole until it is up to the top then replace the screw. You may have to do this a few mornings in a row to make sure all air is out of the system. Proper bleeding will lower your temps 10 to 12 degrees.

 

Coolant Temp Checks
1. Check that your Fan Clutch is actually spinning up. These do go bad , This should spin up faster at higher tempatures. If your clatch fan stays at normal speed during heaving driving this could mean its bad.
2. Check that your Auxillary Fan is actually turning on when your ac/ is engages. These fail , mine fail i had no idea becasue my guage stayed normal. Replace mine with an after market. (check relays and temp sensor if not engaging)
3. Be sure to replace your factor thermostat with the TD5 180 degree themostat.
4. Check water pump flow, at the reservoir, pull the cap on a cold engine not hot . be sure you have coolant flow seen at the coolant return line which is the top hose. I replaced this with a rubber heater hose instead of the brittle plastic oem.

Not an expert but i am a recent Disco 2 owner. I caught the disco fever..I hate to love them.

 

So i just turned on the engine for a few moments to examine, main radiator fan immediately started spinning and is working well to my observation. (I did turn AC off before i cranked engine over.) So looks like its not the main fan. (AC Fan works as well).

 

I went and bought a ScanGauge 2 today from NAPA and drove 10 mins back home with it connected, I went from 198 degrees to max 204 w/ out AC on in 115 degree heat outside. I have the 190 thermo installed.

 

That sounds right for a 190 thermostat to me, but you need a longer drive about 1/2 and hour

 

So something interesting I DISCOVERED today, my temps from ScanGauge 2 running around city are 198-204. However, when I got home in the past and the coolant blew from the resivour overflow tube, I had had the AC on for the drive. Today, I drove it WITHOUT the AC on and my temps were the same, but NO coolant blow when I got home. ???? I really hope this isn’t head/cracked block, but i will go buy one of those tests.

 

Could be coincidental. If temps are the same, I’d expect pressure in the cooling system to be the same. Only thing that the AC makes different from a cooling perspective is having warmer air pass through the radiator (since it’ll have first gone through the condenser and gotten warmer). If coolant temps were different between AC and no AC then maybe, but seems like the cooling system is working effectively.

I’d add that I’d expect higher coolant temps than you’re running if there was a HG leak into the cooling system. HG leak could also cause coolant leak from the head, but it’s coming out of the overflow... which is weird.

Maybe look into a replacement reservoir cap? Hopefully someone else can chime in. Having the numbers is helpful from a diagnostic perspective.

 

@boston4 @Nicholas Paesler When my head gasket was going I had a similar issue no overheat but over pressurized cooling system. The coolant test did not really detect combustion gases so it was pretty much invalid in my case.

However speaking to several mechanics they all agreed as soon as I described the symptoms head gasket,they were correct a hair line crack leading to a cooling passage

 

I recommend running with the cap 1 turn loose so they don't build pressure. It lowers the boiling point to around 220, but mine never get that hot anyway or if they do I know I have a problem. If you do have a slight hg leak it will allow the pressure to escape without damaging other components and reduce coolant flow in to the engine until you can get it repaired.

 

Thanks for all the help again, guys. I went out and bought a new pressure cap for the resivour tank, and so far things seem to be ok! (maybe thats a good thing, maybe bad). With AC on and about 105 degrees outside, my temps ranged from 197-204 yesterday driving in stop and go traffic. (AC fan and radiator fan are working.) And when I got home and parked, no coolant overflow! The pic below is new cap on left, old (yellow) cap on right. From what everyone has been saying, should I go for a pressure test/coolant flush just in case? And I am looking in to getting the 180 thermo.