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Engine fan not switching off

The coolant system was checked by a Merc dealer, yet the day after the Engine fan did not switch off again, we now have taken the fuse out until I can find a solution for this, I have spend a lot of money already, I feel ripper off

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In some vehicles, engine fan operation is thermostatically controlled and the fan starts and stops independently

Posted on Apr 25, 2013

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2000 cadillac deville is overheating, replaced thermostat: water pump radiator had head gaskets fixed it's saying check coolant level and it spews coolant from the overflow tank cap when hot thoughts?

Two cooling fans controlled by three relay's . If only one fan is working ,that could be a problem .
Coolant Level Sensor Description
The coolant level sensor monitors the coolant level in the cooling system and indicates if the coolant is low. This sensor is located at the base of the radiator surge tank and is not serviceable.
The IPC receives a discrete input from the engine coolant level switch. The engine coolant level switch is normally closed. When the engine coolant is low, the engine coolant level switch opens. When the IPC receives an open signal from the engine coolant level switch, the IPC displays the message on the DIC.

Relay Driven Dual Cooling Fan Diagnostics There are using a pontiac , by your cadillac is the same .

Mar 24, 2017 | 2000 Cadillac DeVille


Cooling system fault finding..

Your cooling system works by pumping coolant(water and antifreeze) through the engine where it absorbs heat, through the radiator (where it loses that heat) and back into the engine.
Main components of the cooling system.
  1. Coolant. It can be plain water. Adding Glycol based antifreeze is definately recommended as it not only raises the boiling point of the water and lowers the freezing point but also contains very important corrosion inhibitors. Adding too much antifreeze lowers the coolant's effectiveness so don't go more than a 50/50 mix unless stated otherwise by the manufacturer.
  2. Radiator. This acts as a heat exchanger between the coolant and outside air. It is actually a whole bunch of small pipes that have thin pieces of metal conncted to them to increase the effective surface area.
  3. Waterpump. Well that's what it is. A pump to circulate the coolant around the engine.
  4. Thermostat. This unit regulates the flow of coolant around the system. You need to get the engine to operating temperature as quick as possible, then you need to keep it there as this aids in lowering fuel consumption and emissions and this is the job of the thermostat. It is installed in the system in such a way that it can block the flow of coolant between the radiator and the engine.
  5. Cooling fan. Cooling fans help airflow through the radiator at low speed or when the vehicle is stationary This may be electrical - powered by a thermostatic switch and a relay, directly driven by a belt off the crankshaft or have a viscous coupling. The viscous coupling is also directly driven but contains a fluid which couples the fan to the pulley only when needed.

Reasons for overheating :
  1. Insufficient coolant
  2. Insufficient circulation of the coolant
  3. Insufficient airflow
  4. Excess heat generation
Do's and dont's
When topping up it is better to use antifreeze only, as you will not be diluting the mixture. When refilling use the correct mix of water and antifreeze or fill with pre-mixed coolant.
Replace coolant according to service schedule.
Never open a hot cooling system.

The first and most obvious thing to check is coolant level.
No reservoir : coolant is added directly to the radiator. Fill to the top. You may find a little fluid missing everytime you open the radiator. This is due to water expanding when heated which escapes through the overflow pipe at the radiator cap.
Non pressurised reservoir. This coolant tank is not pressurised and can be opened at any time. Usually has a cap that just clips on. Fill to the max mark when the engine is hot or at least to the min mark when the engine is cold. If this reservoir is filled it does not nescesarily mean the system is full since it depends on expansion and contraction of air and coolant within the system to get coolant back into the radiator. The radiator should be filled as well.
Pressurised reservoir : Most modern-day vehicles are fitted with this type of system. It is pressurised and should only be opened when the engine has cooled down. Do not overfill, always keep coolant levels between the minimum and maximum marks.
If coolant levels keep dropping with no visible signs of leaking have the engine tested for a blown head gasket.

The internal passageways that allow for coolant flow through the engine are metal and constantly exposed to coolant which causes rust which is transported throughout the system. The radiators' internal pipes have very small diameters and easily become blocked by this rust. This decreases the effective area of the radiator and the amount of water that can pass through it. Regular replacement of the coolant will prevent this build-up.
Waterpump impellers may break and decrease the efficiency of the pump although this is rare.
A slipping fan belt will also cause decreased coolant flow but is usually quite noticeable as a high pitched shrieking noise especially on startup and when revving the engine.
The thermostat is in effect a valve which opens and closes with temperature. They go faulty mostly because of rust and scale buildup and can get stuck in a closed or half-open position, thereby blocking waterflow to the radiator.

The radiator fins are spaced closely together so can easily catch debris such as bugs and grass which will impede airflow through the radiator. The fan assists with airflow so if not working will see the engine overheat when stationary or in stop-start traffic. If the engine cools down while driving above 35mph this is the obvious starting point.

Incorrect fuel/air mixture and incorrect ignition timing may cause the engine to generate heat in exess of the coolings systems' capabilities.

How to test and repair :
  • Check the fluid level. Also check for leaks. They will usually show up as brown or green streaks of dried coolant.
  • Check your fan belt/serpentine belt - is it still intact? Check the operation of the fan. On a direct coupling you should not be able to move the fan. A viscous coupling should not spin freely by more than a quarter turn. See below for the electrical fan.
  • Flush the system. Remove the upper and lower radiator hoses and if possible, remove the radiator. Stick a hosepipe into the outlet side of the radiator and let the water run until it comes out clear on the other side. Then repeat the process with the hosepipe in the inlet side. Continue with this until the water runs absolutely clear.Now remove the thermostat from the engine and do the same to the engine. Clear the radiator fins of bugs and debris.
  • Check the thermostat. It should be in the closed position. Drop it in a cup of boiling water and you will notice it opening. Since it is already out you may as well replace it since it is relatively inexpensive
Electric fan
On an electric radiator fan, let the vehicle heat up to just before overheating. If by this time the fan has not come on switch off the engine.Locate the cooling fan fuse and check that it is intact. Using a multimeter, measure between each of its' contacts and earth. See diagram. Measure between 1 and earth(bare metal point on vehicle body or on battery negative), and then between 2 and earth. Both readings should be 12V or more with the ignition on. If 1 reading is found only, the fuse is faulty. If no reading is found the wiring between the ignition and fuse is faulty.

Now check the operation of the fan itself. Disconnect the fan. Connect a lead wirefrom the battery negative to one of the fan connector pins and from thebattery positive to the other pin. See diagram: 1 - Fan motor
2 and 3 - Connect directly to battery


This is a DC motor so polarity doesnot matter. If the fan operates reconnect it to the harness. If not, replace the fan.
Locate thefan relay. You will need a multimeter to test. Remove the relay. Switch on the ignition. Measure voltage at allthe connections in the relay socket to earth. Two of them have to be at 12V or more. If not, the problem is between thefuse and the relay. Re-insert the relay.
Disconnect the thermoswitch. Usually located on the radiator. See photo : 1 - Thermostatic switch. 2- Leaked and dried coolant on a neglected radiator.

Shortcircuit the 2 wires from the harness that were a moment ago connected to the thermo switch.(With a single wire thermo switch the wire needs to be connected to earth or battery negative). Switch on the ignition. The fan should start running again. If not switch off the ignition and remove the relay again. You already know the connecting point with 12V. Measure the other 3 wires for resistance to earth. One of themshould read more than 5 ohm. Connect a lead between the "12V" connector and the "5ohm" connector. Switch ignition on. If the fan runs the relay is faulty. If not the wiring between the relay and fan is faulty.
Simplified wiring diagram:
A- Battery
B - Ignition Switch
C - Fuses
D - Relay
E - Thermostatic switch
F - Radiator fan


Leak detection
The most obvious tell-tale would be a puddle of coolant under the vehicle after a trip. Don't confuse this with condensation dripping from the aircon.
Inspect pipes for cracks and leaking at joints.
Inspect the radiator for dried coolant. (See photo above)
Inspect the engine block for coolant streaks. Leaks can start on the block itself through the welch plugs which are also constantly exposed to coolant.
Another leak point is the water pump shaft seal which cannot be repaired. Replace the whole pump.
Remember that the cabin heater is plumbed into the cooling system and can also leak. Wet carpeting in the footwell is indicative of this although such wet carpeting may also be the result of condensation from the A/C.

How to wire a relay

on Sep 17, 2010 | Nissan Sentra Cars & Trucks


Over heating

Cold engine - - check that coolant level is correct - Ignition on but engine not running - set heter temp settings to max - set fan manual to one of the lower speeds - start engine and within 30 seconds rev it 3-4 times up to 3000rpm - shut off engine before end of 30 seconds (before it starts to heat) - reset climate to normal settings - recheck coolant and top up if necessary. Hot engine. - take car for a run to get up to operating temp - using caution - slowly open the bleed valve (steam and bubbles may come out) - close as soon as you see liquid coolant without excessive bubbles. - do not overtighten this as they are plastic threads. Just snug till it seals fully. - after engine cools check the coolant level again and top up if necessary. Check coolant level every few days for a few weeks and top up again if required - repeat the Hot engine bleed process again. If coolant keeps droping after 2-3 top ups have the system pressure tested. If you are still getting over temps have it analysed by a dealer. The temp is controlled by the engine computer so there may be another fault.

on May 19, 2008 | 2006 BMW 545i

1 Answer

Trying to install a coolant fan switch.

It is almost always mounted in the radiator or next to the thermostat housing,do not mistake Cooling Fan Switch Operation:
00115_cooling_fan_switch.jpgThe cooling fan switch on electric fans monitors coolant temperature signals from the engine control computer. When the engine is cool, the switch opens to keep the fan from spinning. When engine is warm, the switch closes to turn fan on for cooling. How To Instructions:
Inspect - Check for obvious problems.
Test - Give it an in-depth diagnosis.
Replace - Out with the old, in with the new.
the coolant temp sensor for the fan switch.

Jul 06, 2012 | 2005 Honda Element

2 Answers

Heat gauge moves up and down, the fan fan does not come on.VW POLO 2004 1.4i

sounds like a bad connection somewhere check your ground from the engine and body, to the battery. check all connections to all sensors in the rad and the coolant bungs, get them squared away best as possible.

if that's not the remedy check coolant level if the fan switch is not submersed in coolant it will not turn on the fan. and the same goes with the temp sensor the level may be right at the sensor but below the fan switch. If the coolant is low top it up. check it again in a couple days.

if the coolant in low again check for white smoke out the tail pipe. depending on your technical skills you may at this point want to bring it to a garage for leak down test and compression test. Good luck!

Mar 08, 2010 | 2002 Volkswagen Golf

2 Answers


Did you replace the fan? How about the fan switch?

Here is some stuff to read about this system....please let me know what's up!

This switch is the primary controller of the operation of the radiator fan(s) used for cooling. When the coolant in the system reaches a pre-determined temperature, the fan switch closes and completes a circuit. The fans will be brought on. Generally, the switch communicates with the fan relay, although the later PGM-FI cars send the signal through one of the many solid-state controllers first. Do not assume that the switch is the only component in the radiator fan circuit which controls its operation. There are many other components whose failure may prevent the radiator fan from operating. If the fans are not working when the engine is very warm, check the fuses first.
On all vehicles except 1990-95 Accords and 1992-95 Preludes, the fan switch is located in the bottom of the radiator. On 1990-95 Accords (except V-6) and 1992-95 Preludes, the switch is located in the housing at the rear end of the coolant connecting pipe. This is the pipe running along the outside of the engine, just above the oil filter. The switch the only electrical component in the housing. On the Accord V-6, it threaded into the side of the coolant crossover pipe (not next to the bleed bolt) on the transaxle side of the engine.

Nov 19, 2009 | 1991 Honda Accord

2 Answers

I have not seen the coolant fan operate lately although we are mainly highway driving which i understand it shuts off. fuses ok , ac also stopped working. how do i test the fan or relay and could this also...

Coolant fans are turned on by a heat sensitive switch, your engine temperature may not be getting hot enough for it to come on.
One way to test it is let the vehicle idle and keep an eye on the temperature gauge, do not let it get into the red!!
The fan should start around half way or there about, if it does not start and you are nearing the red mark, shut the engine down and let it cool off.
There is only a few simple parts to check...
(1) Check the fan is free moving and has not locked up, you can also test the fan by unplugging it and hooking 12volts to it.
(2) Check the fan relay, see if there is another in the fuse box you can temporary swap with, it should be of the same type, if unsure do not try this.
(3) The sensor switch may be bad, if your engine temperature is up high enough, this switch should close.
You may even need to take it to a dealer and have them do a quick look at it, with a lot of highway use the fan will seldom come on, only when you sit in traffic will it operate or on a hot day.

Aug 25, 2009 | 2002 Saturn Sl

2 Answers

Engine warning light on all the time been to

check the plastic connectors in the cooling system.vw is notorious for the plastic stuff cracking causing a slow leak

Jul 19, 2009 | 2000 Volkswagen Beetle

2 Answers

2004 Prius Check Engine Light - code POA93

P0A93 is an inverter cooling problem. The inverter is cooled by a dedicated cooling system, which consists of an electric water pump, cooling fan, and radiator. This cooling system is independent of the engine cooling system.The mechanic should check if there is sufficient amount of coolant for the inverter, check if the coolant hose is not bent or clogged, if the water pump / cooling fan motor connections are ok, and of course if both of the cooling fan motors are OK.

P3108 is generally loosing communication with the A/C system control module. This can usually be solved by checking the wires and or the converter inverter assembly.

Jun 17, 2008 | 2004 Toyota Prius

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