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2003 Discovery 2 SE7
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Discussion Starter #1
Took my D2 up on the highway for the first time yesterday. I noticed two things:
  • It drives remarkably well at highway speeds - far better than I expected, and
  • It runs much hotter than I expected.
I have a 180-degree thermostat in it, and despite this, I saw a peak of 206 degrees on the readout (OBDII Bluetooth adapter + the Torque app on my phone), with average temp somewhere around 201-202.
Ambient outside temperature was 90 degrees, the A/C was on full, and it was a hilly stretch (rolling hills, not mountains or anything that steep or long). 65-75 MPH, 2,000-2,500 RPM, never came out of 4th gear in Drive, not aggressive driving at all.
It only came back to under 200 after a 3/4-mile-long downhill with me staying off the gas. On consistent flat level ground, it runs at 198-200 at these speeds.
Usually driving around at lower speeds on back roads and around town (30-45 MPH) it runs at 188-194 degrees.
I replaced all of the coolant hoses when I replaced the thermostat (except heater hoses), replaced the coolant, and bled the system as per the RAVE, so I highly doubt there are air bubbles in the system or anything like that.
It is also worth noting that my truck is lighter than stock because I removed all of the rear seats. It was just me driving - no passengers or cargo.
Knowing full well that these engines can have many heat-related problems, this concern me a little bit, especially since I want to use the truck to tow and haul things in the future, which would only make everything hotter. Are these kind of temps normal? If not, why are they so high, and how should I go about fixing it?
Thanks in advance.
 

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What 180 Thermostat,if it is a whitish Motorad then that is normal, they not seem to really be 180's. I run a Black 78c from Bearmach in my 04 and fully loaded for 3 day off road and a roof top tent I never break 188.6 on the flats at 50-65 and about 195 -197 max on very long steep uphills. I drop to as low as 175 on long coasting down hills. I turned the air on, as a test, there was no appreciable difference but it is not very warm here currently

I found the gray 180 soft spring to be more stable but I ran higher temps at idle.
 

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2003 Discovery 2 SE7
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Discussion Starter #3
It is the black Bearmach 78C. I have had it in there for about a month, and it operates at a consistent 188.6-190.4 when the ambient temps are around 70 degrees. In those kind of temperatures, I have seen as low as 177 on downhills, with the hottest being 197 when going up a steep hill (at around 45 MPH, around half throttle, 3,000 RPM). This is the same setup - completely unloaded, no rear seats, etc. Idle temp never exceeds 195.8, even with AC and the hot ambient temps we have been experiencing here recently - in cooler temperatures, it never breaks 194. I guess it just doesn't really like the high outside temperatures combined with the high engine load at comparably low RPM when driving on the highway. Thanks for the help.
 

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Drives like an old man
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Those numbers sound about right. I don't think you have a problem. The temperature rating on the thermostat only determines at what temperature it begins to open, not the final temp. You're right in the sweet spot.
 

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A lot of forum members freak out at anything >200F, but the aux fan doesn't even come on until 212, I recall.
 

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very disco
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If you’re getting consistent, reproducible temps... then I’d be content. Expect higher operating temps when the ambient air is warmer.

like it has been said many times, the thermostat doesn’t control your engine coolant temp, it only controls WHEN your cooling system starts flowing through the engine.
 

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2003 Discovery 2 SE7
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Discussion Starter #8
Thanks for the help everyone. Sounds like I should be fine - the temps are consistent and repeatable, and I took it out again today on the same stretch of highway and only hit a max of 203 - it was around 80F outside today.

A lot of forum members freak out at anything >200F, but the aux fan doesn't even come on until 212, I recall.
Good to know. Does the aux fan also occasionally come on with the AC? I had the truck idling for a while in a parking lot with the AC on, and it came on even when the coolant temp was only at 195. I brought the revs up a little (like 1300) for around 20 seconds to get the mechanical fan and water pump spinning faster - that dropped the temp down to 190, but the aux fan kept going. It shut off sometime after I started driving again.
 

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The electric fan is not only for aircon, it's second purpose is to protect the engine when it gets too hot and as LR considers it's too hot only at 212 and swithces it of ar 202 i'd say that when it's hot outside you are OK, also the original thermostat was supposed to be fully opened only at 204 so IMO those who are stressed by temps around 200 are exagerating ... though it's possible that the viscous fan to not lock well if it's old then it will not pull air well, try to stop the blades with a rolled up newspaper when the radiator is hot and if you can you need a new one


Electric fan V8.jpg
 
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Discussion Starter #10
The electric fan is not only for aircon, it's second purpose is to protect the engine when it gets too hot and as LR considers it's too hot only at 212 and swithces it of ar 202 i'd say that when it's hot outside you are OK, also the original thermostat was supposed to be fully opened only at 204 so IMO those who are stressed by temps around 200 are exagerating ... though it's possible that the viscous fan to not lock well if it's old then it will not pull air well, try to stop the blades with a rolled up newspaper when the radiator is hot and if you can you need a new one


View attachment 92118
Interesting. Thanks for the info. I will be sure to test my viscous fan the way you describe and will replace if necessary. Thanks again.
 

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Drives like an old man
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Interesting. Thanks for the info. I will be sure to test my viscous fan the way you describe and will replace if necessary. Thanks again.
And just for the record, you can take any advice from Sierrafery as absolute gospel. He knows of what he speaks, as has been proven dozens of times.
 

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Discussion Starter #13
And just for the record, you can take any advice from Sierrafery as absolute gospel. He knows of what he speaks, as has been proven dozens of times.
That's what I figured. I have never seen anyone with so much clear, in-depth knowledge of a subject, complete with visual aids and clear explanations. I have found his replies to be immensely helpful.
 
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