Cooling fan operation
04-17-2005, 01:31 AM
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Cooling fan operation
I couldn't find an exact match for this problem, but I'm sure it's been discussed before:
I just replaced the cooling fan switch on the radiator. As the car warmed up (don't know exactly how much, since the gauge is very erratic), both fans came on (AC is Off). The problem is, they didn't shut off.
If I shut off the engine (ignition), one fan continued to run for a long time, then stopped. If I turn on the ignition during this time, both fans come back on.
It's been so long since I've driven this car, I don't remember how the cooling fans are supposed to work. Isn't just ONE supposed to come on with a rise in coolant temperature, and BOTH if you have the AC turned on?
The temperature gauge didn't drop much, but at least it stopped rising. Makes no difference with the hood open or closed. I ran out of time to take any IR readings or do any other testing, but I'll try tomorrow.
I'm thinking that the radiator is either blocked or corroded (it was replaced several years ago). Can I have it cleaned at a radiator shop, or should I just buy a new one? Should I remove the radiator and back flush it with a hose myself, instead? Recommendations welcome.
. . . Steve
I just replaced the cooling fan switch on the radiator. As the car warmed up (don't know exactly how much, since the gauge is very erratic), both fans came on (AC is Off). The problem is, they didn't shut off.
If I shut off the engine (ignition), one fan continued to run for a long time, then stopped. If I turn on the ignition during this time, both fans come back on.
It's been so long since I've driven this car, I don't remember how the cooling fans are supposed to work. Isn't just ONE supposed to come on with a rise in coolant temperature, and BOTH if you have the AC turned on?
The temperature gauge didn't drop much, but at least it stopped rising. Makes no difference with the hood open or closed. I ran out of time to take any IR readings or do any other testing, but I'll try tomorrow.
I'm thinking that the radiator is either blocked or corroded (it was replaced several years ago). Can I have it cleaned at a radiator shop, or should I just buy a new one? Should I remove the radiator and back flush it with a hose myself, instead? Recommendations welcome.
. . . Steve
04-17-2005, 01:38 AM
#4
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You most likely have a bad ground somewhere, or even a bad temperature gauge.
Use clarks-garage to test the relay, fan fuses and possibly bleed the system as well.
http://www.clarks-garage.com/shop-manual/cool-01.htm
Use clarks-garage to test the relay, fan fuses and possibly bleed the system as well.
http://www.clarks-garage.com/shop-manual/cool-01.htm
04-17-2005, 10:58 AM
#6
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On the early cars BOTH fans run when the A/C is on and\or the radiator is hot and the ignition is on.
One fan (driver side) runs at slow speed when the radiator is hot and the ignition is off.
If the driver side fan is running (ignition off), and you turn the ignition on, BOTH fans run.
When the driver side fan stops you should be able to turn the ignition on without any fans running.
On the early cars BOTH fans run when the A/C is on and\or the radiator is hot and the ignition is on.
One fan (driver side) runs at slow speed when the radiator is hot and the ignition is off.
If the driver side fan is running (ignition off), and you turn the ignition on, BOTH fans run.
When the driver side fan stops you should be able to turn the ignition on without any fans running.
04-18-2005, 03:17 AM
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Thanks! My fans run the way they are supposed to, except they don't shut off if the engine is running. I took IR temperature measurements today, aiming at a spot about 1" away from the bottom inlet and the top outlet hoses. Both started around 79F. When the top hose got to about 170F, the fans came on. The bottom hose was about 90F at the time. The bottom hose temperature rose to around 110F, and the top dropped to 150F or so.
The fans were still running. A few minutes later, the bottom hose again read about 90F and the top hose was up at 160F - indicating that the thermostat was closed? This doesn't make sense to me.
When I shut off the engine, bottom hose was at 100F, top at 160F. When the slow fan turned off, both temperatures were around 170F!
These are "average" temperatures, for it depends on where the IR gun is pointed, how far away it is, if there's any interference, etc. Of course, they are just the temperatures of the hose, not the water. However, the temperatures should be fairly proportional to the actual temperature.
Are these measurements in the right ballpark? Why did the temperature in the bottom hose increase, then decrease? Could this fluctuation be caused by trapped air?
I'm pullin' the radiator tomorrow and going to take it to a radiator shop to see if they can clean it. Other than just replace it, I don't know what else to do.
The fans were still running. A few minutes later, the bottom hose again read about 90F and the top hose was up at 160F - indicating that the thermostat was closed? This doesn't make sense to me.
When I shut off the engine, bottom hose was at 100F, top at 160F. When the slow fan turned off, both temperatures were around 170F!
These are "average" temperatures, for it depends on where the IR gun is pointed, how far away it is, if there's any interference, etc. Of course, they are just the temperatures of the hose, not the water. However, the temperatures should be fairly proportional to the actual temperature.
Are these measurements in the right ballpark? Why did the temperature in the bottom hose increase, then decrease? Could this fluctuation be caused by trapped air?
I'm pullin' the radiator tomorrow and going to take it to a radiator shop to see if they can clean it. Other than just replace it, I don't know what else to do.
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04-18-2005, 09:37 AM
#8
Three Wheelin'
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When the cooling system is operating properly the fans will cycle on and off while the engine is at idle.
What you may be seeing is a "fight" between the thermostat and the radiator temperature switch. This can happen if you install a low temp radiator switch and leave the stock thermostat inplace, or if the thermostat is sticking/not opening fully.
Since you are going to pull the radiator, you might as well pull lthe lower radiator hose so you can get to the thermostat which is in the INLET to the water pump. This sucker can be a real PITA to get out.
The T-Stat is held in with a large snap ring, and is situated such that "normal" snap ring pliers are just about useless. What I do is use an awl or similar pointed tool to pry on one "ear" of the snap ring and then I use a small flat tip screwdriver to pry the ring out. This will take some time and swearing, but it can be done.
Once you get the T-Stat out, put a pan of water on the stove and "cook" the T-Stat. Use a thermometer (I have a dual channel Fluke J/K Thermocuple) to determine the opening temperature.
FYI, I'm dealing with a similar situation with my 951. The engine runs OK, the fans run, belts are tensioned (did a retension two weeks ago), but the temperature doesn't really drop when the engine is at idle. If I "blip" the throttle or put the car in motion the temperature drops and will steady out at a "normal" temperature. I've also noticed that the driver side of the radiator is noticeably hotter than the passenger side. This is telling me that there is flow, but it is not flowing fast enough and I suspect either a partially clogged radiator or a bad T-Stat. I've been running some Pesetone Cooling System Flush for the last couple of days, (this is the "6 running hour" type, not the "quickie" 10 minute stuff) and some time this week I plan to drain, flush, and then refill with straight water and see what happens. If the cooling is still poor, then I'll pull the T-Stat and test it.
When the cooling system is operating properly the fans will cycle on and off while the engine is at idle.
What you may be seeing is a "fight" between the thermostat and the radiator temperature switch. This can happen if you install a low temp radiator switch and leave the stock thermostat inplace, or if the thermostat is sticking/not opening fully.
Since you are going to pull the radiator, you might as well pull lthe lower radiator hose so you can get to the thermostat which is in the INLET to the water pump. This sucker can be a real PITA to get out.
The T-Stat is held in with a large snap ring, and is situated such that "normal" snap ring pliers are just about useless. What I do is use an awl or similar pointed tool to pry on one "ear" of the snap ring and then I use a small flat tip screwdriver to pry the ring out. This will take some time and swearing, but it can be done.
Once you get the T-Stat out, put a pan of water on the stove and "cook" the T-Stat. Use a thermometer (I have a dual channel Fluke J/K Thermocuple) to determine the opening temperature.
FYI, I'm dealing with a similar situation with my 951. The engine runs OK, the fans run, belts are tensioned (did a retension two weeks ago), but the temperature doesn't really drop when the engine is at idle. If I "blip" the throttle or put the car in motion the temperature drops and will steady out at a "normal" temperature. I've also noticed that the driver side of the radiator is noticeably hotter than the passenger side. This is telling me that there is flow, but it is not flowing fast enough and I suspect either a partially clogged radiator or a bad T-Stat. I've been running some Pesetone Cooling System Flush for the last couple of days, (this is the "6 running hour" type, not the "quickie" 10 minute stuff) and some time this week I plan to drain, flush, and then refill with straight water and see what happens. If the cooling is still poor, then I'll pull the T-Stat and test it.
04-19-2005, 01:53 AM
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Man! I just knew someone was going to tell me to remove the thermostat! It is a real PITA. I bought a long-handled bent needle nose plier at Harbor Freight and ground down the tips to fit. It works, but it's still a pain to get to those stupid holes in the retaining ring.
I thought I installed a low temp thermostat, but could be wrong. I have a new one to try, so I probably don't need to do all the testing you describe.
I dropped off my radiator at a shop today. He will remove the plastic ends and rod the tubes, put it back together, and pressure test it for $50. I figure that's about 1/4 of the cost of a new radiator, so I'll try it.
I thought I installed a low temp thermostat, but could be wrong. I have a new one to try, so I probably don't need to do all the testing you describe.
I dropped off my radiator at a shop today. He will remove the plastic ends and rod the tubes, put it back together, and pressure test it for $50. I figure that's about 1/4 of the cost of a new radiator, so I'll try it.
