W124 320CE EngineTemperature

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fredbenz

New Member
Joined
Sep 2, 2014
Messages
19
Location
Darkest Wiltshire
Car
W124 320ce
Been a while since I've posted but been following the site with interest and learning along the way. I've had my W124 320CE around 3 years now, it's my 1st Mercedes and yes, members were right when advising that they certainly grow on you.....................it's a fine car and a joy to drive. I've suspected that the temperature reading on the dashboard is unrealistically low so took advantage of the very hot conditions to try and get the dash reading above it's usual 60 degrees [well mid way between the '40' and the '80' on the clock anyway]. I failed, despite outside temperature of 30+ degrees even after an energetic motorway drive the dashboard still read it's customary '60' degrees. Incidentally, the aircon was on and the recently fitted new radiator currently has only distilled water in it. I imagine that members 'in the know' will be all to familiar with this situation; I would be grateful for your views on whether I've a problem here and if so how to track down the cause and rectify it.

Regards
Steven
 
I have a feeling they were set up to very quickly show a minimum temp for frost and ice conditions and were not meant at all to show maximums with any degree of timeliness. Would that match with what you are experiencing...?
 
The symptoms make me think that the thermostat is stuck open - or missing altogether! This allows the coolant to flow throught radiator constantly, especially from cold, so normal operating temperature is rarely reached.
 
Mine also reads consistently implausibly low, despite changing the thermostat. I find it less worrying than if it were consistently high....
 
Mine also reads consistently implausibly low, despite changing the thermostat. I find it less worrying than if it were consistently high....
Presumably the other causes might be a faulty sender or a faulty gauge, but the first one is probably a lot easier to replace. It should be the sensor with a single pin on top of the thermostat housing, but check by getting the engine warm and then pulling off the connector. You should see a reaction on the gauge.
 
I have a feeling they were set up to very quickly show a minimum temp for frost and ice conditions and were not meant at all to show maximums with any degree of timeliness. Would that match with what you are experiencing...?
The needle on the dial certainly moves from rest to around 60 degrees quickly enough as the engine warms up, it is just that regardless of factors it doesn't go any higher - I would have expected my recent drive in really hot conditions would have registered some temperature increase on the dial.
 
The symptoms make me think that the thermostat is stuck open - or missing altogether! This allows the coolant to flow throught radiator constantly, especially from cold, so normal operating temperature is rarely reached.
I know that the thermostat isn't missing, it's only about a year old and was fitted when the new radiator was done. Of course this doesn't mean that the thermostat functions properly now.
 
Presumably the other causes might be a faulty sender or a faulty gauge, but the first one is probably a lot easier to replace. It should be the sensor with a single pin on top of the thermostat housing, but check by getting the engine warm and then pulling off the connector. You should see a reaction on the gauge.
Thanks for the reply, I'll do the sender test when I can. As coupe addict says in his reply, he experiences implausibly low temperature readings.
 
Clunk! I thought you were talking OTG. May-be cross check the temp with a thermometer adjacent to the sensor.
 
You mention that your new radiator has just distilled water in it. Although what I write will not solve your problem, I would recommend that you add Mercedes recommended antifreeze as it contains a rust inhibitor and I believe, it will reduce any electrolytic action between the cast iron engine block and the alloy head.
 
Put an infra red thermometer on the thermostat housing and check the reading. You might have a bad sender.
 
You mention that your new radiator has just distilled water in it. Although what I write will not solve your problem, I would recommend that you add Mercedes recommended antifreeze as it contains a rust inhibitor and I believe, it will reduce any electrolytic action between the cast iron engine block and the alloy head.
Thanks for the timely advice, I'll certainly do so. I've been using surplus distilled water, generated by our domestic dehumidifier, to gradually flush the engine................I'm making progress, the water when drained from the radiator is getting cleaner each time I drain it. Couple more flushes and I'll put water and coolant / anti freeze in intending it to be permanent, well before winter sets in.
 
I don't think I would worry too much about this. Our 280 is pretty much the same and has been this way for years. It only ever gets warmer when its really hot - mid 30s in Italy at the moment and running uphill under load.
 
Do you have an engine oil cooler on your car...?
 
One has to suspect the sensor or its wiring/connector- IIRC these are an NTC [ negative temperature coefficient] device = as the temperature of the sensor rises its resistance falls and the reading on the gauge rises. Anything that increases resistance in the wiring [ corroded connector?] would give a falsely low reading--check the wiring and connections are clean.
typical resistance values for the single pin sensor might be
single wire = Temp Sender for Coolant Temp Gauge in dash.
DIGITAL VOLTMETER set to resistance measurement (resistance, one probe on sensor pin , other probe on Chassis/engine) as follows:
Cold ~ approx 1000ohms
Warm ~ approx 145ohms (around 50deg on temp display in dash)
Hot ~ approx 70ohms (around 80deg on temp display in dash)


Mercedes-Benz W124 Coolant Temperature Sensors Replacement | 1986-1995 E-Class | Pelican Parts DIY Maintenance Article
 
One has to suspect the sensor or its wiring/connector- IIRC these are an NTC [ negative temperature coefficient] device = as the temperature of the sensor rises its resistance falls and the reading on the gauge rises. Anything that increases resistance in the wiring [ corroded connector?] would give a falsely low reading--check the wiring and connections are clean.
typical resistance values for the single pin sensor might be
single wire = Temp Sender for Coolant Temp Gauge in dash.
DIGITAL VOLTMETER set to resistance measurement (resistance, one probe on sensor pin , other probe on Chassis/engine) as follows:
Cold ~ approx 1000ohms
Warm ~ approx 145ohms (around 50deg on temp display in dash)
Hot ~ approx 70ohms (around 80deg on temp display in dash)


Mercedes-Benz W124 Coolant Temperature Sensors Replacement | 1986-1995 E-Class | Pelican Parts DIY Maintenance Article
Many thanks Graeme for your very helpful test, explanation and link. I'll check the car when I'm able, which may not be until the weekend. Incidentally, the loom was refurbished by Sileck less than 1K miles ago - at that time connectors were clean but I accept there is no substitute for checking them now though.

Regards

Steven
 
Do you have an engine oil cooler on your car...?
I've had to do a bit of research having been floored by your question [I really hadn't a clue!] Seems that the engine oil cooler, if fitted, is co-located and directly in front of the oil filter housing. From a couple of images I've seen [of what I think is the engine oil cooler] I would describe it as a small irregular shaped alluminium looking 'box' with many external webs in the casting and a couple of what appear to be oil line connections on one face - hopefully this is what I should be looking for. Anyway, I've found that getting a line of sight into that area has been tricky but from various attempts and some partial views some using mirror, the engine oil cooler does appear to be there on my car. Sorry for the long winded response, I think I'm trying to say '' yes, I think so''.
 
Another thing to check is that the sender is not in a pocket of air. If you loosen it off slightly you can bleed any air out.
 
I am not sure how it is plumbed but would imagine there is a thermo device to stop the oil being cooled too much, perhaps Dr. grober & others may have some insight into this device...??

If it is what it may be it rings true that it would be designed to fail safe and provide cooling all the time.
 

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