My 2003 VW Passat W8 engine fans turns on when the engine starts and runs all the time until the engine is turned off, in which time it will run for another 2-3 minutes. This started about 2 days ago. Could this be a faulty coolant sensor or fan relay that is stuck open? Thanks, Ron

no enigine told gas or diesel.
i cant see what you are doing
rules :
never run any pump dry, it is fuel lubricated and cooled.
if engine cranks and will not run (not told you)
then measure pump pressure only cranking, cranking matters. PSI cranking only matters, dead engine,.
some cars have key on prime pulse others do not. or based on air temps, yes/no. rules complex. avoid prime pump tests. (savvy?)
some new bosch pumps are 100% silent so noise tests are not good now, use use cranking PSI pressure only if wise. and hate taking a bath in fuel.
11vdc to pump pins cranked. (11vdc is battery resistance drop)
PSI cranked.
that is what matters.

below is battery voltage drop cranked, all 100% good
see the alternator wake-up, IT MUST./
11vdc cranked and 10.5 to pump (ohms laws Vdrop normal)

scopes RULE!

Either you installed the wrong temperature sensor or the new one is bad or bad wiring.

Has coolant level been going down in return reservoir at all, as in have you had to add coolant recently to bring it up to top level? Have you tried running engine from cold, with heater on and let it run up to normal temperature with cap off return reservoir? If not do so, and watch level in reservoir and if it goes down, add as needed until engine running at normal, and not overheating. Allow rad fan to kick on & off a few times before re-installing cap on reservoir. Pay close attention to engine temp while doing this. If it goes high, shut it off and let cool. Be careful, my son's Passat just had overheat problem and turned out to be impeller on water pump ( internally) was spinning on shaft of pump. Thermostat is certainly a consideration if coolant is full, and all air bled out. Keep me posted on what happens when you run with cap off and keep reservoir full. Don't forget, heater on while doing this.

Sounds like the engine timing may need some adjusting. Try this:

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I know that on the earlier model VW's there was an underhood thermostatic switch for the electric fans. This switch would keep the fans running until the underhood temperature reached a desired level. If this switch were to go bad, it would most definitely cause the problem that you are describing.

The fan should still run if the engine is very hot,even after most cars are switched off. The battery may be on its last legs.Try this test, before you switch off the engine,put your heaters on full speed,open your windows if you cant stand the heat lol.This should help cool the engine and help shorten the time your engine fan needs to run to bring down the temp. If the battery is still draining,the alternator may be the culprit. This can be tested with a multi-meter.

check the relays for your fans and check you fuses for yourfans

its not normal.its a coolant temp sensor which has malfunctioned causing the ecu to think the engine is hot even when its not.hence the fan on for so long after ignition switched off.the sensor needs to be changed and put on a diagnostic machine afterwards.just bring it to a garage.

go to a tool store and ask for an easy-out, this is a specialty tool placed on a drill to grip stripped screws and broken bolts

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Good Luck