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[Seanscrap]

Neither Radiator fan or Ac fan is coming on (the small fan in the relay box does come on tho) the car is overheating, touching the pins on the plug in the relay compartment shows both fans work on both speeds,  I  Have changed basically all the relays to new ones changed all 3 of the sensors (Bottom Radiator) And two in the engine next to the thermostat, (have removed the thermostat for now to allow it to heat up slower on short journeys) Have cheeked the water pump and coolant flow and levels All Ok!   running out of things to try... wanted to see if anyone Had any answers or solutions?   Many Thanks Guys

[Doctor Gollum]

Do the fans spin freely?

Regardless of the relays, the fans are switched by the thermoswitches in the radiator.

Removing the thermostat may well be preventing the coolant from ever getting hot enough to turn the fans on...

[Entwood]

There used to be a guide to testing the fans/switches .. it came from t'other place .... not sure if its in the guides here .. I'll go searching ...

that was far too simple ...   https://www.omegaowners.com/forum/index.php?topic=133825.0

[Doctor Gollum]

There used to be a guide to testing the fans/switches .. it came from t'other place .... not sure if its in the guides here .. I'll go searching ...

that was far too simple ...   https://www.omegaowners.com/forum/index.php?topic=133825.0

Been done reading between the lines

[Seanscrap]

Thanks for the reply’s Fellas   some more ideas to work through forgot to add that the water is at boiling point and the overheating light (red) comes on...   I’m sure it’s something electrical Will keep playing around with it      Any more ideas that I can try Fire Away       

[Doctor Gollum]

Coolant temp gauge is a separate sensor.

Fans are controlled by actual coolant temp, not the gauge, with an over ride from the engine ecu.

Engine ecu has its own coolant temp sensor.

Live data would confirm that your gauge sender is toast, especially if it's overheating without a thermostat.

[Nick W]

Start with the easy stuff, and make each system work:


Put the bloody thermostat back in! On modern engines it's important for how water flows through the engine.
A diesel runs cold, so much so that many haven't needed the fan for years, and the thing is seized.
Is it actually overheating - that means blowing water out of the expansion tank. Check  the reading from the ECUs sender, it's a different part from the gauge one.
Check the temperature into and out of the radiator, there should be a big difference.
Check the thermo switches for the fans(the AC one not working suggests a wiring fault. But you do need to check) and the associated wiring.
Is the system properly bled?
Have the coolant checked for combustion gasses, this is a big cause of engines pressurising very quickly. That means a head gasket, or worse, fault.






Some of this will require tools: a <£10 multi-meter is essential for the electrical faults; you might manage the ECU reading with a cheap OBD scantool; a cheap laser thermometer will do the temp checks and is also good for playing with the cat; combustion gas test is best farmed out.


Don't just swap parts unless you have proved they are faulty!

[Seanscrap]

I have replaced this temp sensor (the one next to the thermostat) with a brand new one and have even tried the old one back in, Although the new one seemed like a cheap aftermarket copy when it turned up basically looked the same tho but Thinking I will aim to order a genuine now  (obviously and put the thermostat back in) and see if I get any change  Thanks Fingers crossed

[Seanscrap]

Have a multi meter and checked the voltages in and out of the relays and to the fan etc. I haven’t done the temp check tho as haven’t got a temp gun so will have a go at this also

[Doctor Gollum]

There are TWO sensors.

Test BOTH of them.

[Seanscrap]

I have changed the coolant sensor in the Bottom of the Rad and the one by the thermostat also the gauge one next to it or is there another one

[Seanscrap]

“Check  the reading from the ECUs sender” Also how do you check this?

[Seanscrap]

Should also add have tried the AC on to see if the AC fan would come on that way but no joy so neither Fans coming on made me think it was electrical Have tried to trace what wiring I can see (hoping for a broken wire) but wiring looks all good... cars only on 80,000 or so and looks in excellent condition 

[Doctor Gollum]

Ok, let's simplify this as dropping snippets won't help anyone... 

The gauge tells you that the engine overheats. The fans don't spin.

You have changed:

Thermoswitch(es) on rad
Coolant temp ecu (Bosch plug)
Coolant temp gauge (spade terminal)
3 fan relays

You've removed the thermostat

Anything else that you have/haven't done?

Does the aircon work? That has an over ride effect on all fans.

Do the fans actually spin by hand?

[Seanscrap]

Appreciate the replies:) so Yes changed all three of these,  the fans do spin very freely and smooth by hand and spin of an external power and by touching the relay together (with its housing cover taken off) Have replaced about 4 or 5 relays  ‘any of the ones linked to the fan Have been changed for new ones). Have also got a brand new water pump although haven’t fitted that as the water flow through the system is running flowing well and have topped up with new coolant as water was lost in changing the Rad sensor