I've got the scangauge set up to monitor the coolant temp (among other things), and as I was driving Tristan over mountains this weekend, I noticed the coolant temperature dropped.

Tristan normally runs consistently in the 215-220F range, but on this weekend's trip the coolant temperature dipped rather alarmingly as he climbed any of the hills on the route. This was most apparent going over the Altamont pass from Tracy, the road goes from zero altitude to 755ft in just a few miles on I-580, while doing about 70MPH. He started at 218 at the bottom and got down to 179 just over the summit.

Is this at all normal? It certainly surprised me. It doesn't sound like a good idea, theoretically, the engine is less efficient when running at lower temeratures.

I could imagine that the ECU sees the extra load and preemptively increases cooling, but it seems to be over doing it. Other possible explanations I can think of are the drop in pressure, or the drop in temperature as you go up the mountain affects the cooling. The pressure would drop about 1/2 a PSI, nd the temperature drops about 5F (from about 85-90).

 

Boiling temperature drops at higher altitude.

 

This is my first post ever, as I've been motoring too much lately to reply to anything, but anyway, it must be something normal, because I've noticed it a few times as well. Normally I run 220-225 on my ScanGauge, but on hot days (90+ outside) my temp drops to around 180 around town. At least I can rest easy knowing I'm not the only one.

 

But only by a degree or 2 upto 775 feet, not by 40 degrees. The system must be pressurised as its running above normal boiling point anyway.

 

Sorry, you are correct, jumped conclusion when I read "Mountain"

In addition to thermostat MINI has an extra temperature control in form of a waterpump feed clutch that holds coolant circulation until warm.

Would expect A/C to turn electric fan on for max airflow over condenser if front of radiator.

I don't have scanguage, but am surprised to see a 30-40 f degree variance in engine coolant temperature reported.

Pressurized yes, but usually at 16# or so above ambient and so it would be less total pressure at high altitude, agree that 755' would be minimal, but 7,550 would be noticable. Open Hot Thermos SLOWLY

 

I've worked out that its definitely the engine load which causes this. The Scangauge also has a load gauge ("LOD") which tells you 0-99 how hard the ECU thinks the engine is working. If you put a consistent load of above about 75 on the engine the coolant temperature drops. Usually on the flat the load is transient, ie you get up to speed and ease off, so you never see this.

I tried this by flooring it at low revs (ie high gear) on the flat (loads around 95), and eventually the temp drops. Also if I lift off going up hill to keep the load below about 75 the temperature stays constant. So either the ECU is overdoing the cooling, or the temperature is being deliberatly lowered. I'm not sure if an engine will produce more power at lower temperatures, I do know that an engine will be less efficient at lower temperatures.

I'm also wondering how accurate the temp sensor is, it makes me want to put my own sensor under there to check the temp really is dropping.

Tristan was the dealer yesterday to get something else fixed, I also asked about this, the service advisor came up with some BS about the readings being delayed. This totally does not explain things, but as long as they're not worried about this, I don't mind. I also topped up the coolant to make sure that wasn't the problem, that made no difference. I found a local road where I could reproduce the effect so I could test out the theories. That's be 280 between Cupertino and Alpine road. That's quite undulating and several of the hills will show the effect. The hill doesn't have to be that long or steep.

 

Luckily, on my Clubman, I have no idea what the water temperature, oil temperature, oil pressure, engine load, or voltmeter readings are. Ignorance is bliss. At least we still get a dipstick!

 

I also worked out this happens with MCSs as well, at least Shawn does the same thing. However, its a little more difficult to put an MCS under such a high load for long enough. Running over the same bumps which caused Trisan to peg his load to 99, Shawn would barely show 50. A taller hill would show the drop in temp, as would flooring at low revs and high gear, but you're going rather fast before you start to see the temp dropping.

 

When your engine gets too hot the car kicks the fan into "higher" gear causing more cooling and dropping it below what is normal in more temperate temperatures... come on people it is not rocket science!

 

Maybe not rocket science, but your theory doesn't explain it. The engine doesn't get hot, the temp reading never rises from normal, it just starts plummeting. Also what you're describing is a thermostat. They're designed to keep the temperature stable, there's obviously one of those, the temerature's quite stable under low load conditions. The odd thing about this is the temperature is not stable. It more like bi-stable, there are 2 different temperatures the engine stabilises at.

 

The 'Prince' Engines have a waterpump that is controled by the ECU and only printed reference was that it delays circulation for faster 'warm-up' of a cold engine.

My pure guess for reason you are seeing these lower temperatures at high engine load would be that ECU is reducing chance of 'burn' of exhaust valves at high load by lowering operating temperature.

I know that aircraft engines reduce exhaust valve temperature by using excessive fuel (overly rich mixture) at high power settings.

 

When the ECU senses a rise in coolant temp due to extra load, it kicks in both fans and lowers the temperature. They are both large fans for such a small engine, very simple.

 

It acts more like its sensing the load directly, rather than waiting for any temperature rise.

 

There's a really good explanation (well, it sounds good anyway) on another thread:
https://www.northamericanmotoring.co...is-normal.html
See the miniDave answer about 10 items down the thread.

 

Really? You all just noticed this? It's perfecly normal operation.

The ECU will run the water pump at full speed, fully open the thermostat, and turn on the engine fan with increased load. It will also do it when the AC is set to MAX. You can watch the temp on a scangauge and see it go from 220ish to about 178 pretty quickly.

 

When the engine coolant temperature reaches about 221 the Radiator Fan turns on. You can hear it and also feel it in the steering wheel (very slight vibration) and when it is on the temperature drops.

 

Actually it is post #65 on page 3.