Getting some strange coolant temp anomalies on the VSE. New ECT sensor (Delphi) fitted as part of the head replacement job.
Diagnostics temp high, gauge temp low. Both wrong compared to actual measured.
The ECT sensor on the Thor is a dual thermistor type- one feeding gauge, other engine management. Plug can only go on one way.
Does anyone know whether both thermistors are same value? I have temp/ volts/ kOhm values from the Bosch SID for the ECU side of the sensor, but can't find anything for the gauge side.
Ta!
Have you tried measuring the resistance of both? For any given temperature they will both give the same reading if they are the same value. Have you tried the old one you took out, or at least measured it's resistances? Working on the theory that the gauge one feeds the BeCM it is unlikely the signal it expects to see would be different between a GEMS and Thor engine even though GEMS uses two separate ones as you know but I can only find specs for the one feeding the ECM not the one feeding the gauge. What actual temperatures are you getting?
I can't help with the readings I'm afraid, but have you checked the wiring at the plug? I had a strange no start issue, that turned out to be the insulation cracking off and a couple of wires shorting together in the plug to the sensor. Temperature read as 140 odd degrees on the nanocom.
Actual temps- idling during warm-up:
IR thermometer on manifold where sensor sits- 64C
Temperature gauge- just into blue sector (that's as far as it rises)
Nano on ECU 108C
Coolant at expansion tank- 88C
Eh? they don't make sense. Surely the manifold temperature should be higher than the expansion tank temperature? Can you check the temp at the top hose outlet? That would be the most accurate I would have thought. Temperature reported by Nano seems very high though. The gauge is very heavily buffered and hardly moves at all between 85 and 105 degrees. Not ideal as when it starts to noticeably climb you are almost into an overheat.
I'm playing hunt the air lock as well, as it did a favourable impression of a geyser from the expansion tank when the stat opened! It hasn't moved outside the workshop yet.
Just needed thermistor data to remove some variables (ie test it). Last thing I want is to cook the rebuilt engine.
FWIW on the old sensor gauge side reads 0.7k, Motronic side reads 1.5k. so, if that sensor's not faulty, the thermistor values are different. I'll check the new one. Who knows, it could have been built backwards! The plug only fits one way.
Did another idling run from cold to 100c indicated on Nano, when its panic alarm went off. Temp gauge got to nearly top of blue. IR temperature of top hose (and LPG reducer, heater feed, and rad top got to 60c. rad bottom 30c.
As an aside, still getting air burps back through expansion tank, which is strange. Have pressure tested system and its held steady 15 psi for 30 mins so I haven't royally f**cked up installing the heads!
Time to drain the top of the cooling system, pull the alternator and get stuck into the sensor i suppose, but will do some voltage checks at ECM first, so I can see what it's seeing compared to what it should be seeing...
Interesting results at ECM connector. Much lower voltages than should be, but pretty linear:
Temp (top hose)_ Actual _ Should be
39_1.73 __ 2.75
44_1.58 __ 2.4
48_1.27 __ 2.2
50_1.13 __ 2.1
53_0.975 _ 2.0
59_ 0.76 _ 1.7
62_ 0.7 __ 1.6
65 __ 0.68 _ 1.5
That would suggest you have a higher resistance thermistor than you should but from your checks with the old one, the ECM sensor is the higher of the two so that would discount the possibility that the internal wiring is reversed.
I'm scratching my head trying to make sense of this, so, thinking out loud, just talking engine ECM for now...
As measured temperature goes up, resistance and voltage drop. As voltage "seen" by ECm is lower then ECM will give a diagnostics temperature as higher than actual. Schoolboy maths on the ratios between "is" volts and "should be" volts comes back with the sort of diagnostics temps that I've been getting.
Time to take the bloody sensor out I think. I'll check resistance of cables, but as there are errors on both sides (BECM and ECM) and the two sides of the sensor have their own separate earths it has to be the sensor. Doesn't explain why the temp gauge is under-reading, but if one thermistor is the wrong value, then it's possible the other is too.
Have to let the thing cool down before I can pull the alternator. Boy this car's hard work...
Orangebean wrote:
I'm scratching my head trying to make sense of this, so, thinking out loud, just talking engine ECM for now...
As measured temperature goes up, resistance and voltage drop. As voltage "seen" by ECm is lower then ECM will give a diagnostics temperature as higher than actual. Schoolboy maths on the ratios between "is" volts and "should be" volts comes back with the sort of diagnostics temps that I've been getting.
Time to take the bloody sensor out I think. I'll check resistance of cables, but as there are errors on both sides (BECM and ECM) and the two sides of the sensor have their own separate earths it has to be the sensor. Doesn't explain why the temp gauge is under-reading, but if one thermistor is the wrong value, then it's possible the other is too.
Have to let the thing cool down before I can pull the alternator. Boy this car's hard work...
If your chasing air locks its possible you might have air stuck round where the sensor sits? So taking it out might help bleeding the air out anyway?
I'd considered that the sensor might be sitting in an air pocket and thus reacting to surface temp rather than immersed probe temp BrianH. As you say, when I fit the new one (after testing it, connected and active on the car in a little pot of boiling water and tracking the readings on the thermometer, voltmeter, Nano and engine temperature gauge as it cools!) I can be as sure as I can that there's coolant coming out around the threads before I tighten it.
No air pocket there:
Tightbutts.com didn't supply a sealing washer with the new genuine part. The old/ new OEM had a sealing washer swaged onto it. Good thing I've got a box of Dowty seals sitting around.
Went wild and bought an in-line bleed fitting to put in the highest of the 19mm hoses. I know you don't need one, but I'm putting it in there to make life easier in future.
So, after a day's faffing around testing senders, cables and earths I settled on fitting the new new one. The old new one was definitely giving bad data on both the BECM and ECU sides. The engine temp gauge now reads correctly- middle of the gauge and all parts on the hot side zapped with the IR thermometer are at or around 90C. Cold side 30-35C.
The ECM is still reading high (around 110C with above data) though although the thermistor resistance for ECM side was ballpark similar to the original one. Makes me swallow deeply and think "what if it is actually 110C?" even though measuring everything with IR thermometer confirms it's not.
So, what next? I'll probably drop in another ECM (handy having spares lying around) and see what happens then. Nice to have the old girl back on the road though, even if it was only to drive home from workshop.
As an afterthought, I'll take an ECM reading tomorrow morning with everything at ambient...
That would make sense. After it's stood overnight the air temperature and coolant temperature should both be the same. If the ECM is still reporting it as high, then you'll at least know by how much. I wonder if it will realise it's reading high and adjust itself? The BeCM does with things like the fuel gauge.
There's a sort of adjustment. According to the SID:
The signal supplied by the engine coolant temperature sensor is critical to many fuel and ignition control strategies. Therefore, the Bosch 5.2.1 system incorporates a complex engine coolant temperature sensor default strategy, which it implements in the event of failure.
The ECM uses several alternative inputs to determine the specific default value selected in these circumstances. The amount of time the engine has been running and the temperature of the air entering the engine are the primary inputs used to determine the default value. The
software model of the temperature increasing will finish when it reaches a value of 150°F (65°C). This value is then used until the engine is switched off.
I guess it'd throw a fault code if it implemented the above. It goes on to say:
The following symptoms may be noticeable in the event of an engine coolant temperature sensor failure:
• The MIL lamp illuminated (after ‘validating’ the fault)
• Poor engine hot and cold start
• Overheat warning lamp (incorporated within the Instrument pack) is illuminated
• Excessively hot or cold needle reading on the temperature gauge.
I don't think that's self calibrating though
What did you find then Mark?
Haven't been out to car yet. Bit of a mini-monsoon going on here.
Just waiting for my sausages to cook, then out into the elements
Looks like it's about to blow over, http://www.raintoday.co.uk/ and that I might get some later. If it arrives when FP3 or quali is on from Monaco that should time it about right, no distractions outside.