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jeremy 14th August 2017 10:02

Temperature
 
Had a few runs (obviously not public country backs) to check engine temp. Running a m50 2.5 lump, temp kept rising , reading 120 on guage, slightly worrying, but when I turned engine off, then put on ignition, it read 88 degrees, and on starting immediately needle shot up to 120 again.... Any ideas?

MartinClan 14th August 2017 13:33

Strange that it jumps like that. I would, initially, check that the gauge is matched to the sensor and that the gauge is receiving the correct supply voltage. Many of the older gauges (Smiths for example) expect a 10v supply.

Cheers, Robin

jeremy 14th August 2017 14:42

Temperature
 
Will start investigating, it's a tailor made smiths from Europa spares, so Defo 12 volt. I have access to a nifty temperature reading gun, which will read temp if block , radiator injectors and expansion bottle... So hope that the temp of 86 is correct and not 120. .

Patrick 15th August 2017 14:13

M20 is happy in the 80-90C region - mine runs 80 until it need the fan and mostly sits at 85 after that.

I seem to remember M50's running quite hot based on the one in my granddads old early model E46 320. But that may have been an issue with his car, went to the dealer a few times because of it when he first got it. Although 120 is a bit excessive !!

Mike 18th August 2017 00:47

Quote:

Originally Posted by jeremy (Post 90078)
Will start investigating, it's a tailor made smiths from Europa spares, so Defo 12 volt. I have access to a nifty temperature reading gun, which will read temp if block , radiator injectors and expansion bottle... So hope that the temp of 86 is correct and not 120. .

Why do you believe your gauge is 12 volt?
The original Smiths gauge was 10 volt, and the one I bought from Merlin Motorsport was 10 volt.

What sender are you using?

I was not happy with my temperature readings either (same M50B25 as yourself). I didn't like the Smiths sender having to be fitted into an adaptor collar to fit into the M50 head port: nor did I like the 10 volt requirement.

In the end I sent my standard BMW VDO sender to Caerbont Automotive (manufacturers of the current Smiths gauges) and had them make me a Smiths Classic faced gauge but with programmable logic in the back which they calibrated at every 2 degrees in a bath of oil to my BMW VDO sender.
I now have a gauge which tells me exactly what the temperature in the head is.
If you are interested they gave it a part number, so you may be able to simply order one off the shelf?

My gauge shows around 90C when driving steadily below 60mph, but rises to 95-100C when pushing along at 75-80mph for prolonged periods on a motorway - (remember water's boiling point is around 110C when the system is pressurised at 13lbs).

Out of interest, I fitted a Ford thermostatic fan switch in my radiator, which is set to come on at 92C and go off at 88C.
Whilst driving over to Wales recently on a 600 mile round trip the fan only cut in when the temp gauge showed 95-100. Initially I was worried by this but then rationalised that the radiator temp, mid way down , will be cooler than the head temperature. Secondly I don't want the fan to be coming on whilst driving at reasonable speeds, but only when in slow traffic or stationary................. or thrashing it on a motorway!).

That said I still nervously wait for the fan to kick in when the temp gauge starts to rise when sitting at traffic lights on a hot day - so far it has done so every time without any sign of boiling.

One last point - I did have a problem with losing water over long distances from the header tank over flow - until I replaced the pressure cap with a new one (13lb). Since then I've not lost any water, despite pushing on at 75-80mph continuously for around 2 hours along the A14/M6/M54 on a very hot day.

jeremy 20th August 2017 11:33

temperature
 
Hi Mike, thanks for that info. I havent had much time to fully investigate yet, but have a few things to check. I know it is a 12 volt guage as is marked and I have the original fitting instructions. I am wondering if the difference in reading on ignition (11.5 volts) and starting (alternator 14 volts) makes a difference. Also the 2 coolant sensors-blue one to ecu, and black one to guages can be checked by taking live readings from my obd diagnostics. I also have the use of a thermal imager which can read any part of the engine for temperature, which may be useful, and I obviously need to check all my wiring again. May get a look tonight when little one asleep.... he wants me to drive him to school in it soon... no pressure!

Mike 21st August 2017 23:24

Quote:

Originally Posted by jeremy (Post 90151)
Hi Mike, thanks for that info. I havent had much time to fully investigate yet, but have a few things to check. I know it is a 12 volt guage as is marked and I have the original fitting instructions. I am wondering if the difference in reading on ignition (11.5 volts) and starting (alternator 14 volts) makes a difference. Also the 2 coolant sensors-blue one to ecu, and black one to guages can be checked by taking live readings from my obd diagnostics. I also have the use of a thermal imager which can read any part of the engine for temperature, which may be useful, and I obviously need to check all my wiring again. May get a look tonight when little one asleep.... he wants me to drive him to school in it soon... no pressure!

Jeremy

Are you using the BMW sender connected to your Smiths gauge, or have you fitted a Smiths sender?

Mike

jeremy 31st August 2017 09:08

temperature
 
Hi Mike , just got a 5 minute look last night, I think I'm using the smiths single wire sender, sitting behind the blue temp sender in the head.

http://www.demon-tweeks.co.uk/motors...classic-gauges

jeremy 9th April 2018 18:32

Temperature
 
Cant believe 8 months since I last got looking at this. A little further forward I believe. I let the engine run, and my guage went up to 120 degrees within 15 mins idle. I then used to different thermal images, both showed 90 degrees. I gave more throttle, and was happy to see radiator glow red at 94 degrees, proving thermostat and cooling system working well. The car was not overheating. I have however still the problem of the guage reading 120, but on turning off engine, on ignition it reads correctly, Im assuming it is a voltage issue, I also found last night that alternator not charging, so more investigation needed.

Grey V8 Pete 10th April 2018 13:23

[.........I also found last night that alternator not charging, so more investigation needed...............]

Jeremy. Before you start pulling things apart, check that the ignition warning light comes on when you switch the ignition on and then goes out after starting the engine. If the bulb has gone then the alternator won't charge as it needs to detect this small current flow to the bulb to tell it to charge! Nearly bought a new alternator years ago until the very helpful Lucas man put me right! Peter.

jeremy 10th April 2018 17:08

Temp/alternator
 
Will do,i have noticed it on and off while running

Grey V8 Pete 11th April 2018 10:07

Quote:

Originally Posted by jeremy (Post 94226)
Will do,i have noticed it on and off while running

Mmm. That could be something internal then. Start with something simple though. With everything switched off pull the wiring plug off the back of the alternator and thoroughly clean the contacts. Replace and see if the problem goes away.

If not start thinking about how old the alternator is? Brushes can be changed easily and slip rings can get dirty and need cleaning. Otherwise you could be looking at replacing the diode pack. If unsure about doing this then have a local auto electrics place check it out. Peter.

jeremy 11th April 2018 13:23

Temperature
 
Thanks for that, I think a likely culprit cud be the terminals or diode as had similar problem before, wondering if proximity to the exhaust manifold could be a factor in failure . Hope to check over weekend.


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