Discussion
Before I start another cooling thread I want to make it clear my car has no cooling issues at all. Never overheats even in traffic for hours on end (it's been tried - not through choice!)
My issue is with the fans. When I hit traffic the fans cut in with a water temp gauge reading of around 88 degrees C (give or take). The temperature in solid traffic will settle about 89-91 degrees C (i.e. the fans steady the temperature rather than cool it, but not at any alarming temperature) and not go higher. Fans stay on permenantly. None of this is a problem.
My concern is that once on the move, the temperature will quickly go down to about 85 or a bit lower (which is good), but the cooling fans stay on, which seems unnecessary. They only go off if I get at least 5 minutes of clear traffic at 60mph plus when the gauge goes back to about 81 or so. Therefore if I am driving around towns the fans will stay on until I turn the engine off. On the race track the car didn't get really hot but was running about 83 or so, fans stayed on the whole time.
I am running a 700hp LS7. Standard Ultima set up.
Do others have similar experiences?
I am thinking of swapping for a rad switch that comes on later and turns off at a higher temperature.
Any thoughts?
Mark
My issue is with the fans. When I hit traffic the fans cut in with a water temp gauge reading of around 88 degrees C (give or take). The temperature in solid traffic will settle about 89-91 degrees C (i.e. the fans steady the temperature rather than cool it, but not at any alarming temperature) and not go higher. Fans stay on permenantly. None of this is a problem.
My concern is that once on the move, the temperature will quickly go down to about 85 or a bit lower (which is good), but the cooling fans stay on, which seems unnecessary. They only go off if I get at least 5 minutes of clear traffic at 60mph plus when the gauge goes back to about 81 or so. Therefore if I am driving around towns the fans will stay on until I turn the engine off. On the race track the car didn't get really hot but was running about 83 or so, fans stayed on the whole time.
I am running a 700hp LS7. Standard Ultima set up.
Do others have similar experiences?
I am thinking of swapping for a rad switch that comes on later and turns off at a higher temperature.
Any thoughts?
Mark
Best solution is to move to "speed controlled" fans. Plenty of OEM modules that are reasonably easy to adapt to do this. This way the speed of the cooling fans is proportional to the temperature over the set point, and they don't suddenly start and stop at a particular temp! Pretty much all OEM vehicles are now like this for NVH and energy saving reasons
mt308 said:
Before I start another cooling thread I want to make it clear my car has no cooling issues at all. Never overheats even in traffic for hours on end (it's been tried - not through choice!)
My issue is with the fans. When I hit traffic the fans cut in with a water temp gauge reading of around 88 degrees C (give or take). The temperature in solid traffic will settle about 89-91 degrees C (i.e. the fans steady the temperature rather than cool it, but not at any alarming temperature) and not go higher. Fans stay on permenantly. None of this is a problem.
My concern is that once on the move, the temperature will quickly go down to about 85 or a bit lower (which is good), but the cooling fans stay on, which seems unnecessary. They only go off if I get at least 5 minutes of clear traffic at 60mph plus when the gauge goes back to about 81 or so. Therefore if I am driving around towns the fans will stay on until I turn the engine off. On the race track the car didn't get really hot but was running about 83 or so, fans stayed on the whole time.
I am running a 700hp LS7. Standard Ultima set up.
Do others have similar experiences?
I am thinking of swapping for a rad switch that comes on later and turns off at a higher temperature.
Any thoughts?
Mark
Given LS thermostats open at 90 degrees it sounds like you set up is doing its job, just hanging in for too long, it seems your sensor has quite a bit of hysteresis built in (ecu?), I have no idea if this is standard,My issue is with the fans. When I hit traffic the fans cut in with a water temp gauge reading of around 88 degrees C (give or take). The temperature in solid traffic will settle about 89-91 degrees C (i.e. the fans steady the temperature rather than cool it, but not at any alarming temperature) and not go higher. Fans stay on permenantly. None of this is a problem.
My concern is that once on the move, the temperature will quickly go down to about 85 or a bit lower (which is good), but the cooling fans stay on, which seems unnecessary. They only go off if I get at least 5 minutes of clear traffic at 60mph plus when the gauge goes back to about 81 or so. Therefore if I am driving around towns the fans will stay on until I turn the engine off. On the race track the car didn't get really hot but was running about 83 or so, fans stayed on the whole time.
I am running a 700hp LS7. Standard Ultima set up.
Do others have similar experiences?
I am thinking of swapping for a rad switch that comes on later and turns off at a higher temperature.
Any thoughts?
Mark
certainly mine has a narrower margin between on and off (nearer 5 degrees) comes on at around 93-94 and off again at 88-89.
have a look around and see if you can adjust the setting in the ECU, if not put a switch in, or go for Max's OEM variable speed module set up.
With rear engined, front radiatored cars, you don't generally need a lot of hysterisis in the fan temp switching setpoint, because the system already has a fair degree of "lag" in it.
I.E. your engine coolant temp sensor, mounted usually close to the thermostat outlet on the engine says "fan on", and the fan starts to cool the water in the radiator, that is some distance away from the engine. That fan stays on until that cold(er) water gets all the way back to the engine, and through the engine, then the sensor drops enough it says "fan off". This means the average temperature tends to oscillate more than for a system where the rad is close to the engine. Depending on the filtering on the coolant temp input your ecu uses, you can get away with as little as 2degC hysterisis. It's also worth setting the "on" temp significantly higher than the normal running temp to prevent the fan running when the vehicle is moving or unecessarily in stop-start traffic.
I.E. your engine coolant temp sensor, mounted usually close to the thermostat outlet on the engine says "fan on", and the fan starts to cool the water in the radiator, that is some distance away from the engine. That fan stays on until that cold(er) water gets all the way back to the engine, and through the engine, then the sensor drops enough it says "fan off". This means the average temperature tends to oscillate more than for a system where the rad is close to the engine. Depending on the filtering on the coolant temp input your ecu uses, you can get away with as little as 2degC hysterisis. It's also worth setting the "on" temp significantly higher than the normal running temp to prevent the fan running when the vehicle is moving or unecessarily in stop-start traffic.
Max_Torque said:
With rear engined, front radiatored cars, you don't generally need a lot of hysterisis in the fan temp switching setpoint, because the system already has a fair degree of "lag" in it.
I.E. your engine coolant temp sensor, mounted usually close to the thermostat outlet on the engine says "fan on", and the fan starts to cool the water in the radiator, that is some distance away from the engine. That fan stays on until that cold(er) water gets all the way back to the engine, and through the engine, then the sensor drops enough it says "fan off". This means the average temperature tends to oscillate more than for a system where the rad is close to the engine. Depending on the filtering on the coolant temp input your ecu uses, you can get away with as little as 2degC hysterisis. It's also worth setting the "on" temp significantly higher than the normal running temp to prevent the fan running when the vehicle is moving or unecessarily in stop-start traffic.
The fan is controlled by a switch on the radiator, the ECU I believe takes a reading from where you state.I.E. your engine coolant temp sensor, mounted usually close to the thermostat outlet on the engine says "fan on", and the fan starts to cool the water in the radiator, that is some distance away from the engine. That fan stays on until that cold(er) water gets all the way back to the engine, and through the engine, then the sensor drops enough it says "fan off". This means the average temperature tends to oscillate more than for a system where the rad is close to the engine. Depending on the filtering on the coolant temp input your ecu uses, you can get away with as little as 2degC hysterisis. It's also worth setting the "on" temp significantly higher than the normal running temp to prevent the fan running when the vehicle is moving or unecessarily in stop-start traffic.
If you have an ecu with a spare PWM output channel and can assign that output to be modified by coolant temperature (Most aftermarket ECUs like Motec etc enable you to do this) you can just run an OEM fan speed controller, which look like this:
The little silver box mounted on the fan, which takes 12Vdc power feed and usually a 100hz pwm signal. It drives the fan in proportion to that signal "on time". One nice function is that if it doesn't see any signal, it simply drives the fan at full power, so wiring failures from your controller don't lead to an overheating engine.
If you don't have a suitable ecu to output that 100Hz signal, it's very easy to use a little circuit consisting of a 555 timer or small microcontroller to generate that signal in relation to the input voltage from the normal engine coolant temperature sensor
The little silver box mounted on the fan, which takes 12Vdc power feed and usually a 100hz pwm signal. It drives the fan in proportion to that signal "on time". One nice function is that if it doesn't see any signal, it simply drives the fan at full power, so wiring failures from your controller don't lead to an overheating engine.
If you don't have a suitable ecu to output that 100Hz signal, it's very easy to use a little circuit consisting of a 555 timer or small microcontroller to generate that signal in relation to the input voltage from the normal engine coolant temperature sensor
Been for a run with ECU hooked up to my PC. The ECU water temp reading is remarkably stable, warming up quite quickly to around 88. Fans come on when around 91 on (86 on gauage). Doesn't then get hotter than 89-90.
When on the run in open road my temp gauge quite quickly gets down to around 82 degrees, ECU temp reading again remarkably stable at 87-88. Fans still on for a about 15 minutes even though going about 80 in open traffic....
Fans finally turn off when ECU at 88 and gauge at 82 or so.
Interesting the gauge moves around more than the ECU which seems to stay in a 3 degree band once warmed up.
My rad switch is meant to come on at 92 and off at 87. If ECU is the accurate one that 5 degree change just isn't happening. What I really want is a switch that comes on at 92 and off at 90 say, but I don't think one exists (if I stick with the current set up rather than the ECU set up as suggested). The next switch up is a 97-92 which feels too hot....
I'm all for keeping it simple if I can and taking the temp at the rad makes sense to me as thats where the fans will be cooling...
Mark
When on the run in open road my temp gauge quite quickly gets down to around 82 degrees, ECU temp reading again remarkably stable at 87-88. Fans still on for a about 15 minutes even though going about 80 in open traffic....
Fans finally turn off when ECU at 88 and gauge at 82 or so.
Interesting the gauge moves around more than the ECU which seems to stay in a 3 degree band once warmed up.
My rad switch is meant to come on at 92 and off at 87. If ECU is the accurate one that 5 degree change just isn't happening. What I really want is a switch that comes on at 92 and off at 90 say, but I don't think one exists (if I stick with the current set up rather than the ECU set up as suggested). The next switch up is a 97-92 which feels too hot....
I'm all for keeping it simple if I can and taking the temp at the rad makes sense to me as thats where the fans will be cooling...
Mark
As an easy option I have swapped the fan switch from a 92/87 to a 97/92 switch.
The fan now comes on when both ECU and gauge are reading 97 (consistent with the temperature at the switch interestingly). Fans quite quickly bring the temperature on both the ECU and gauge down to 91 or so, even completely stationery sitting in my garage (or in traffic). They stay on permanantly as they don't quite get it back down to the level required to turn the fans off.
When on the move again ECU at about 89 and gauge around 87 or so the fans switch off. Unlike previously where I had to drive for over 10 minutes at 70mph plus to switch fans off, now 30 seconds or so at 30-40 mph gets the fans off again - so unless on a motorway at decent speed in clean air I was driving around with the fans on full time before (which is what I wanted to fix).
I think this is much better behaviour - as long as a few seconds at 97 degrees is not a problem for the engine? I understand that some cars run close to 100 normally (the LS7 in a Corvette I am told runs at 96)...(my new Seat Leon Cupra has a live monitor you can bring up on the dashboard which seems to stay at 90 the whole time!).
Note - the Ultima seems to run in clean air with ECU at around 87-88 or so but with the gauge showing about 82.
I run a fan override switch as well, so if I suddenly hit traffic I will use that anyway rather than wait for the switch to come on itself.
Quick question - for those than run the fans off the ECU directly, please can you let me know at what temperature the ECU turns the fans on and off?
The fan now comes on when both ECU and gauge are reading 97 (consistent with the temperature at the switch interestingly). Fans quite quickly bring the temperature on both the ECU and gauge down to 91 or so, even completely stationery sitting in my garage (or in traffic). They stay on permanantly as they don't quite get it back down to the level required to turn the fans off.
When on the move again ECU at about 89 and gauge around 87 or so the fans switch off. Unlike previously where I had to drive for over 10 minutes at 70mph plus to switch fans off, now 30 seconds or so at 30-40 mph gets the fans off again - so unless on a motorway at decent speed in clean air I was driving around with the fans on full time before (which is what I wanted to fix).
I think this is much better behaviour - as long as a few seconds at 97 degrees is not a problem for the engine? I understand that some cars run close to 100 normally (the LS7 in a Corvette I am told runs at 96)...(my new Seat Leon Cupra has a live monitor you can bring up on the dashboard which seems to stay at 90 the whole time!).
Note - the Ultima seems to run in clean air with ECU at around 87-88 or so but with the gauge showing about 82.
I run a fan override switch as well, so if I suddenly hit traffic I will use that anyway rather than wait for the switch to come on itself.
Quick question - for those than run the fans off the ECU directly, please can you let me know at what temperature the ECU turns the fans on and off?
Edited by mt308 on Sunday 28th September 18:48
The engine doesn't really care what temperature it is at. In fact, it will quite happily run at 120degC top hose, and only loose a couple of BHP doing so!
The issue is keeping the bulk coolant temp below the point where the vapour pressure causes the header cap to vent and the system to loose water! Most caps these days are around 1.4bar, and will allow normal operation to around 110-115 degC top hose.
I wouldn't bother with the override switch, the automatic one will do the job just fine!
The issue is keeping the bulk coolant temp below the point where the vapour pressure causes the header cap to vent and the system to loose water! Most caps these days are around 1.4bar, and will allow normal operation to around 110-115 degC top hose.
I wouldn't bother with the override switch, the automatic one will do the job just fine!
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