Engine temps (revisited)

[philster]

My W202 (C180, 1994) temp gauge has a tenedency to rise in warm weather/London traffic. However, it has never gone above 100 and ususally goes down again once I get moving. Some earlier correspondence on this site reassured me that the gauge going up to 100 was not unheard of, especially as I don't appear to have an electric fan fitted (just a viscous one).

However, this weekend, I was stuck in some medium traffic in London for about 20 mins or so and the weather was reasonably muggy (but not hot, by any stretch). My temp gauge shot up to almost 120 - not too far off the red zone).

Does anyone know what is going on here? Do I have a serious problem, or is this normal (surely not)? I had a service not two months ago, so the coolant level should be fine (although perhaps I should re-check the level), there are no apparent leaks of fluid and the viscous fan does not appear loose.

Would appreciate any thoughts........

 

[Ade]

I've a similar scenario with my W124 230TE so I'd also be interested to learn more. I can't recall the fan ever cutting in but no ill effects seem to be apparent. How do you check the sensor to know if it's working or not?

 

[NormanB]

Philster and Ade

Here a couple of tips.

On these forums there is a mine of information which you can access using the 'search' function.

If you read my post at the following link you will be able to sort (hopefully) and with a bit of luck will only cost £16 ish. Anyway the tests are easy peasy.

http://forums.mercedesclub.org.uk/viewtopic.php?t=6286

Let us know how you get on - and feel free to come back to me with any

 

[Ade]

Norman

Doh! Read your thread with interest as well!

Thanks for the reminder!

Will change sensor and let you know.

Ade

PS At what Temp gauge reading does your fan now cut in at?

 

[Ade]

Norman

Doh! Read your thread with interest as well!

Thanks for the reminder!

Will change sensor and let you know.

Ade

PS At what Temp gauge reading does your fan now cut in at?

 

[philster]

Guys - I've read a lot of correspondence about "fans cutting in" etc. I do not believe that I have an electric fan triggered by a sensor or thermostat. At least I can't see one (I am not massively mechanical, for which apologies). And the viscous fan surely whirrs all the time, and does not cut in and out.

Norm - do your notes relate to the viscous fan or are they only relevant to an electric fan jobby?

 

[NormanB]

Norman

Doh! Read your thread with interest as well!

Thanks for the reminder!

Will change sensor and let you know.

Ade

PS At what Temp gauge reading does your fan now cut in at?

Ade - no point changing the sensor if bridging the harness does not lock the fan clutch! Do the tests!!

IIRC my viscous fan locks up at around 105 deg C (as best as I could guess by the instrumental panel).

 

[NormanB]

Guys - I've read a lot of correspondence about "fans cutting in" etc. I do not believe that I have an electric fan triggered by a sensor or thermostat. At least I can't see one (I am not massively mechanical, for which apologies). And the viscous fan surely whirrs all the time, and does not cut in and out.

Norm - do your notes relate to the viscous fan or are they only relevant to an electric fan jobby?

Hi philtser

I would love to help you - but my crystal ball has developed a wee bit of a problem and I can not see your car very clearly - oh wait - its a Mercedes oh no - the ball has gone cloudy again :wink:

This is a hint to add your car details to your profile!!

The viscous fan will 'windmill' in the airflow, but will not be driven by the engine because the electro magnetic clutch is not energised - that is when your engine temp is below 105 ish deg C. With the car stopped, and engine at idle the fan will still windmill.

As the temp sensor detects that temp or above the switch closes and the electro magnetic clutch is energised - locking the clutch which will now be driven by the engine - until the temp drops below -say 95 (but don't quote me - just principles here).

The carrot test is used in lieu of a finger (which you may use if you have a surplus :wink: ) to discriminate on if the fan is being driven or just windmilling.

Read the linked post with the above in mind.

TTFN :wink:

NormanB

 

[mike65]

What happens if the fan does'nt activate when the terminals are bridged?

Mike.

 

[Ade]

That's a good question Mike.

Thanks for the help Norman

 

[NormanB]

What happens if the fan does'nt activate when the terminals are bridged?

Mike.

If the fan clutch does not lock up (I assume you are doing test with engine stopped but ignition on) and you are able to turn the fan by hand then the cheap repair option has disappeared because the fan is f'd. I do know if there is a repair option other than replacing the whole fan unit.

But I am sure they are around in the breakers and if still on the vehicle are easy to test!

NormanB

 

[philster]

So, Norman, I understand how to perform the switch bridging check. I will definitely try this later.

Would appreciate if you could confirm what the various test results mean..... Here's my understanding:

(1) If you bridge the terminals with the copper wire and you do not hear a clunk, and the fan continues to windmill, then the swich is faulty and needs replacing.

(2) If you bridge the terminals, hear the clunk, but the fan still windmills, (or even stops), and is still moveable by hand, then the switch is fine, but the fan unit is broken, right?

(3) If you bridge the terminals, hear a clunk and the fan locks up and is not moveable by hand, then all is OK? Presumably, the reason why the fan merely locks, ready to turn under the engine's power, but does not actually turn, is because the engine is off whilst I am doing the test (only the ignition is on ie key partly turned)?!?!

If it is scenario 3, then presumable everything is OK in this department and my temp probs lie elsewhere......? We can cross that bridge when if come to it...!

Would appreciate your confirm, else I will be performing this seemingly great little test, without properly understanding the results.

Cheers.

 

[NormanB]

So, Norman, I understand how to perform the switch bridging check. I will definitely try this later.

Would appreciate if you could confirm what the various test results mean..... Here's my understanding:

(1) If you bridge the terminals with the copper wire and you do not hear a clunk, and the fan continues to windmill, then the swich is faulty and needs replacing. No the fan clutch is faulty

(2) If you bridge the terminals, hear the clunk, but the fan still windmills, (or even stops), and is still moveable by hand, then the switch is fine, but the fan unit is broken, right? No this just tells you the fan clutch is not working - it tells you nothing about the thermo sensor

(3) If you bridge the terminals, hear a clunk and the fan locks up and is not moveable by hand, then all is OK? Sort of - you have proved the electro magnetic clutch works. Presumably, the reason why the fan merely locks, ready to turn under the engine's power, but does not actually turn, is because the engine is off whilst I am doing the test (only the ignition is on ie key partly turned)?!?! Correct if the engine was running ( and you can do this if you wish ) with this result then the fan would be driven at engine speed and capable of processing loads of carrots ;-)
If it is scenario 3, then presumable everything is OK in this department and my temp probs lie elsewhere......? We can cross that bridge when if come to it...! No it means the thermo sensor is duff

Would appreciate your confirm, else I will be performing this seemingly great little test, without properly understanding the results.

Cheers.

The viscous fan would be driven at engine speed all the time if there was no thermo sensor in the circuit. This would be bad for economy (power loss driving fan) and very slow warm up times - paricularly in winter. Hence the thermosensor to activate the fan clutch only when required -105 deg C. This would only normally occur in UK if you are stuck in traffic - once you are moving the air ramming thro the rad is normally enough.

The test is simple there are essentially 2 components that you are examining.

1. The fan clutch.

2. The thermo sensor.

If your engine is going above 105 deg C and the fan does not cut in either 1 or 2 (or both) are duff - if the tests prove the fan clutch is OK then ipso facto it must be the thermo sensor.

NormanB