Strange cooling system behaviour
Discussion
(Also posted in Elise/Exige/Europa/340R forum, but this forum seems to have a wider spread of expertise hence its appearance here)
Just had the head gasket replaced on a standard Elise 111S (K-Series VVC). The water pump and thermostat were also changed. The cooling system has been bled.
Prior to this work, the engine would warm up quickly and then hold a rock solid 88 degs whilst in motion. At idle/stationery the temp would slowly rise and stop at 96 degs in winter and trigger the fans in summer which would bring the temp down to 96.
Since the work the temp fluctuates between 88 and 92 when cruising at constant speed and throttle - fair enough, maybe the new thermostat is slightly lazy. What's more worrying though is that once the engine speed rises above 4000, the temperature starts to drop. The longer the engine spends above 4000 the further the temp drops. After 15-20 seconds the temperature has reached 71 degs and the display disappears. I can only assume the temp continues to drop. This happens regardless of throttle position or road speed. It happens on the lightest throttle opening necessary to maintain >4000rpm in second gear, and also at high throttle openings in a high gear.
Has anyone any theories on what is happening and where the problem lies? I'm thinking thermostat, but can't get my head round what would cause the thermostat to display this behaviour.
Grateful for any ideas.
Just had the head gasket replaced on a standard Elise 111S (K-Series VVC). The water pump and thermostat were also changed. The cooling system has been bled.
Prior to this work, the engine would warm up quickly and then hold a rock solid 88 degs whilst in motion. At idle/stationery the temp would slowly rise and stop at 96 degs in winter and trigger the fans in summer which would bring the temp down to 96.
Since the work the temp fluctuates between 88 and 92 when cruising at constant speed and throttle - fair enough, maybe the new thermostat is slightly lazy. What's more worrying though is that once the engine speed rises above 4000, the temperature starts to drop. The longer the engine spends above 4000 the further the temp drops. After 15-20 seconds the temperature has reached 71 degs and the display disappears. I can only assume the temp continues to drop. This happens regardless of throttle position or road speed. It happens on the lightest throttle opening necessary to maintain >4000rpm in second gear, and also at high throttle openings in a high gear.
Has anyone any theories on what is happening and where the problem lies? I'm thinking thermostat, but can't get my head round what would cause the thermostat to display this behaviour.
Grateful for any ideas.
Air heats up quicker than water, so it's probably not air in the system.
Even if you take a thermostat out, when you put the engine under serious load, it'll heat up to proper operating temperature. The only things you can do are check the anti freeze level and make sure there are no air locks. K series can be a bit hard to bleed out, but I'd assume this was done by someone competent.
Have you checked the voltages coming out of your temperature sensor in different conditions? Just because your display shows something, doesn't mean it's true. Second hand data.
Even if you take a thermostat out, when you put the engine under serious load, it'll heat up to proper operating temperature. The only things you can do are check the anti freeze level and make sure there are no air locks. K series can be a bit hard to bleed out, but I'd assume this was done by someone competent.
Have you checked the voltages coming out of your temperature sensor in different conditions? Just because your display shows something, doesn't mean it's true. Second hand data.
cmsapms said:
I'm pretty confident all the air has been bled out. The observed behaviour is over efficient cooling. Wouldn't cavition reduce efficiency leading to raised temps at high pump speed?
Yes, but probably not a raised temperature reading. It may be a good idea to get a temperature probe to figure out what the block and head temperatures are.If air is passing the temp sensor it will read lower (sometimes zero)
These are notorious for air locks and the only thing I have used for Rovers with the same engine is a snap on water filler. It pulls a vacuum on an empty coolant system then when you open a valve that vacuum draws the coolant from a bucket until full. Great bit of kit.
Tony
These are notorious for air locks and the only thing I have used for Rovers with the same engine is a snap on water filler. It pulls a vacuum on an empty coolant system then when you open a valve that vacuum draws the coolant from a bucket until full. Great bit of kit.
Tony
tony g said:
If air is passing the temp sensor it will read lower (sometimes zero)
These are notorious for air locks and the only thing I have used for Rovers with the same engine is a snap on water filler. It pulls a vacuum on an empty coolant system then when you open a valve that vacuum draws the coolant from a bucket until full. Great bit of kit.
Tony
Got a link? sounds interesting.These are notorious for air locks and the only thing I have used for Rovers with the same engine is a snap on water filler. It pulls a vacuum on an empty coolant system then when you open a valve that vacuum draws the coolant from a bucket until full. Great bit of kit.
Tony
There are only two ways that increased engine speed can appear to reduce coolant temperature in a way that is apparently not related to actual load or road speed.
1) The increased water flow is dragging the thermostat open because the return spring is broken or faulty. Easily checked.
2) The temperature sensor is not reading the actual coolant temperature because it's sitting in air when the flow rate goes up i.e. there's an air lock which moves around as the flow pattern changes. Misrouted water hoses creating a non desirable high point or an improperly bled system.
Neither should be any challenge to solve for a bear of average brain.
1) The increased water flow is dragging the thermostat open because the return spring is broken or faulty. Easily checked.
2) The temperature sensor is not reading the actual coolant temperature because it's sitting in air when the flow rate goes up i.e. there's an air lock which moves around as the flow pattern changes. Misrouted water hoses creating a non desirable high point or an improperly bled system.
Neither should be any challenge to solve for a bear of average brain.
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