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Chris J

Coolant temperature drop on higher engine load?

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I'm running a 2011 NA Evora which has an odd thing going on with the coolant temperatures which I don't know if it's  at all normal.  Trundling along at town speeds temperatures warm up to normal (halfway or slightly lower on the gauge) as I'd expect.  If I then have a short spirited drive on the country roads for 5 miles or so,  using more of the rev range,  the temperature vanishes back down the scale.  Usually down to a few pixels above the bottom,  but on a cold night two days ago temperatures dropped right off the bottom of the scale which was more worrying! Going back in to town driving the temperature slowly comes back up. The little sustained motorway driving I do the temperature sits around 1/3 up the scale. 

Last time I was out for an extended drive (back end of the summer) I don't recall anything unusual in temperatures later in the journey.  To my non mechanical mind it's like there's a reservoir of cold coolant somewhere in the system that's being flushed past the temperature sensor once coolant starts circulating when the revs rise. So I don't know if this is normal and a symptom of the short journeys/initial warm up period or something to worry about and indicating a blockage?

 

 

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 I'd considered that, it seems odd that temperatures appear normal during town driving and it underreads during harder driving, or is that a usual symptom for the sensor deteriorating?

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Mine doesn’t behave like this, once warmed up the temperature is pretty stable all the time except in summer traffic when it will go up by one pixel- I wonder if your thermostat is getting sticky (particularly when open) so that when you raise the revs the increased coolant flow drops the temperature. It would be exacerbated by the low air temperatures at the moment too, particularly at speed.

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Sounds like a different thing, but my Elise used to drop about 4 degrees on the digital temp readout after a couple of heavy stabs of the throttle to redline. I imagined this was just due to the increase in coolant circulation with the cooler water in the radiator being pumped around quite quickly - with a bigger impact given the radiator in the front of the car.  Could be wrong, but did it throughout my entire ownership.

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Temperature dropping to the bottom of the scale doesn't sound normal.  Mine does get cooler when I get to stretch its legs a bit and warms up again when going slower ~30mph in traffic.  But the range is from around 50% when bumbling around town and cools down to 30% when driving a bit faster, it won't ever get down to almost zero.

No idea what the problem could be but check the coolant levels are correct?  Is there a way to check the coolant is actually being pumped around correctly?  Or any additional temperature sensors you can access using the OBD2 port and an app on your phone? 

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I'm not sure how clever the cooling system is on these, but my 2015 Cayman did something quite similar.

Porsche make a big thing about how the modern cars are fitted with 'thermal management systems' that effectively react to the type of use and provide cooling accordingly.  They are dry sumped, so this may be a red herring, but modern Porkers definitely run warmer as standard, then add in more cooling as sensors detect more spirited use.  In fact if you look at the oil and water temps on a consistent motorway run and then switch to sport mode, the temps will drop noticeably in anticipation of the increased loads that would then likely to be applied to the engine in that mode.

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The thermostat may also be stuck open and not regulating the temperature properly.

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