Temp Gauge VS Fan Switch Temp Test SE std

[peteoddcar]

Temp Gauge vs Cooling Fans Temps etc.

This evening I decided to refresh my memory by doing a real world test on my car a 90 SE

The findings were not surprising but as expected.

I put a thermocouple into the thermostat housing via the hose fitting for the header tank pipe. The meter placed on the wipe so I could read it on the move if required.
These are the results I got

Gauge TC Temp Meter
Position
1/4 88C
3/8. 96C
1/2. 101C
5/8. 105C
3/4 109C Fans ON at 109C Fans OFF 102C

I repeated this and got good correlation between the two results.

Note 1) The Gauge reacts marginally slower than the fans cool the system.

2) If the engine is revved slightly with fans on the temp drops faster ( No s**t Sherlock) than leaving it at idle.

On the short drive back to my house temp settled about 86C. On Key OFF the temp rise was about 11C.

The fans perform pretty much exactly as it is described in the workshop manual section K page 7.

I just thought I’d add that as a base line.

The absolutely critical part of the M100 turbo cooling system is the recirculation pump. A low temp switch will be making the pump run for far too long for no reason.
I will leave my test set up in place and possibly tomorrow take is for a good blast to really get the turbo and exhaust hot and watch the key OFF ( soak ) effects.
I won’t be changing the fan switch on my car!

[chrism]

As suspected - definitely not a linear progression then.

This excellent data should reassure those who worry that 'it's not in the middle like all the others' or 'it's running too cool' and cement into place that suspicion of a temp sensor mismatch...



My '90 SE thermostat usually cuts in around 82C and the normal warmed-up-running-temp-gauge posn is usually a bit below 1/4.

[Tuga2112]

this is the video peter posted on facebook.which i uploaded with he's permission.

i made it unlisted. in order to make only visible in here and not when peopel search youtube as this without context wont make much sense

[muley]

Really good research carried out here

IMHO it's quite important to have the car running hot enough. Over 100 Deg C is fine as the system is pressurised.

[peteoddcar]

John Lee et al - If the M100 was just a few years later in its design the whole cooling fan / gauge / recirculation pump operation would be software controlled by the ECU. Cars since that era have engine temperatures behave in much the same way sometimes even more extreme - managed by ECU controlled electronic thermostats etc. but the driver is oblivious because the gauge will only respond to an ECU an artificial signal via CAN and will only indicate anything above normal if the engine is severely overheating due to a failure somewhere.
The M100 is a fairly basic ECU even by early 90s standards. It’s a parts bin unit from the Isuzu Piazza Turbo with Lotus mapping. Hardware changes were not on the table. The engineers did the best (we) could using analogue tech in the control system ( relays and diodes ) to overcome a heat soak issue. It’s simple but it works.
Head gaskets - they can fail on any car for a variety BUT I do get why people are alarmed when the gauge goes north with no fans.
In early dealer and customer feed back this was always a complaint and 35 years later continues to be so.
Perception is fact in customers minds.
Lucky most M100 owners are happy to live with the situation.
If they want to over work the fans by making them compete with the thermostat temp. This ideally 10c below fan switch on and about 4c below switch off) fit a lower temp switch.
The pump will run too long ( I like your auto run on idea I might just add one myself )
So in theory a much lower temp stat might help but then the heater wouldn’t be hot enough ( again not and issue for most owners but is for a car designed ant tested for base attributes to GM Worldwide Standards.

[Steve A]

Quality posting Pete

[dapinky]

Pete,

This whole thread, and your excellent input into the situation at the development stage is one of the most interesting articles is recent times...... thank you for putting in the effort to educate us on the whole story and attempt to put to bed the idea of lower temp sender units!

I fully accept that there are going to be some people who live in an area of extreme temperatures, with a cooling system somewhat below it's prime, who may see an actual benefit from the change, but for the rest of us, it is a case of keep it as well maintained as possible, and try to get our minds to accept that what we see is NOT what is actually happening in a meaningful way.

[peteoddcar]

Further information on the gauge / sender. I fear I may have given out some incorrect information in the past.
I firmly believed from my memory that the sender unit was a stock Isuzu unit supplied with the engine as shipped from Isuzu. Investigation of actual parts fitted to my car revealed that my car was footed with a Lotus sender unit it has the Lotus brand icon and a M100 part number stamped into it.
I think it is a unique M100 component.
I tried a selection of standard GM senders most have a metric taper thread that’s very similar the NPT thread so I ran an BPT die and converted the the results were disappointing I can’t recall if I posted but basically the running temp was in the middle and fan in off the scale
I like Geoffs approach!
I intend to play around with a variable fan switch I think a 105 fan on 98 off would be good

[Simon_P]

The fans perform pretty much exactly as it is described in the workshop manual section K page 7...
I won’t be changing the fan switch on my car!

Me either it seems pretty sensible to me not sure why people think 110 C is anything to write home about. Most modern cars operate in the range 90-107 C but you'll notice that the gauge on a eurobox has 90 in the middle at the top and the needle doesn't doesn't move from there (whatever the coolant temp is )

what many forget (or don't realise) is that the simple mechanical thermostat is isn't just open or closed, the 82 C temperature stated is where it starts to open and somewhere in the high 90s it is fully open. So a fan switch that switches off too low is fighting the thermostat.

[chrism]

I intend to play around with a variable fan switch I think a 105 fan on 98 off would be good

peteoddcar, a prev owner fitted this alternative fan control switch to my '90 SE. It's made by 'Rainbow'.

My original wiring has been chopped just above the fan switch - but leaving it in place - and this variable temp control switch has been wired-in and cable-tied near the air filter box. I've adjusted it to 'fans on' at 105C (cos she's a 35-year-old ) and presume it 'fans off' around 97C via the ecu in the normal way.

One reassurance with this is that if I simply wind it down to 0C I can check that rad fans and recirc pump are firing up in the usual way with ign ON or OFF . However, I suspect it might be an 'always on' feature controlled by a relay(?) which might contribute in some way to battery leakage along with alarm, radio, clock etc?

[peteoddcar]

Chris
Concerned that the ignition off state won’t be reading anything or switching due to the lack of power to the electronics.
If that’s the case and the trigger circuit goes open circuit with key off you’ll never get the pump on - that’s BAD
If it’s perm +ve supplied then it’ll be a drain for sure.

Et Al
Just for info we did consider a control module at the development stage. The designers couldn’t have foreseen the heat soak temps being high because the Piazza had no issues - loads of space around the engine for good soak airflow and a lower state of tune, I think that type of data wasn’t communicated well if at all.
Anyway we soon put the module idea to bed because
A) Battery Drain
B) Another bespoke Din relay sized 7 pin unit with the cost and extra D&D work to achieve what a simple relay and diode circuit could manage.

[chrism]

Hi there Peter. When I turn that temp controller down to ambient temp, things seem to work as expected:

1. With IGN OFF the aux recirc fan spins and
2. With IGN ON the twin cooling fans spin.

I seem to vaguely remember reading that a test for these two items is to unplug then earth the temp sensor with IGN OFF and listen for the quiet recirc pump then turn IGN ON and hear the noisy cooling fans?

(Of course I haven't been able to replicate this cos my own temp sensor wire's been cut just above the sensor...)

And surely with my '90 SE (I dunno about the S2) the car's permanently 'powered on', the trigger circuit should get
closed and the pump should work as expected after a hot cooling fan actioned journey? If so it's gotta be perm +ve supplied (and that'll be the source of my/our {fortnightly} power drains for sure)?

Fortunately I use a Cetek battery conditioner - but does this mean that the 'Rainbow' temp controller isn't suitable for the 'always on' m100 OR would it be 'cured' with an aux-posn-before-ign key set up like every other car seems to have?

If that was the case on our m100s surely the aux recirc pump wouldn't spark if you turned all-off after a journey and that would be the same kind of BAD that you mentioned...unless you held the key in the aux posn after IGN OFF 'till the pump cooled down . (silly, I know...)

...questions...questions...

ps Wary of thread hi-jack I only mentioned this controller because it seemed to be a 'ready-made' answer to your next 'play around'...

[Tuga2112]

Chris,

the circuitry from factory (and i bleieve this is the same for both SE and S2) works in a analog manner.
there is only drain if the temerature switch closes the circuit. which then activates the relay
the relay pin itself is permanently powered, but the wire is notconnected to anything until the temperature switch closes the circuit, and drives power to the relay coil.
coil energises and the "click" happens. making the permanently live pin connect to the fans or pump.

if this variable temperature switch you have installed has more than 2 wires connected. its very likely the 3rd wire will feed power to some internal circuitry, that is where the drain would come.

i hope this makes sense.
the bottom line is. within the circuitry of a car. there are some places where things are designed to have an extremely low current always, things like the door locks, ECU memory, temperature relays, and in other cars, the radio units.. these are expected to "drain" the battery, but they are designed to have extremely low currents and they are used to trigger higher current circuits.

My car has a higher static drain than most M100s out there, because i have the radio re-wired (properly) a remote door lock control, and an additional window control module. but my car will stand outside for 3 weeks without a charge and will still start first turn.

very few people understand the electrical system of these cars well, and have no idea how to properly diagnose a parasitic drain. or even recognise what current at the battery is supposed to be considered a parasitic drain. (my guideline is 22-30 miliamps for my yellow car)

the vast majority of aftermarket radios installed in Elans are wired in a manner to be a parasitic drain. instead of properly re-wiring their cars. most folk get battery conditioners.

and im going too far off topic with this Rant. I Have 2 hours footage in my SD card showing how to "properly" wire the radio on the NA... it will make it to youtube one day. but this specific video will get Peter's feedback before it goes public

[chrism]

Thanks Tuga, some excellent info there. I'll certainly check the wiring again but I THINK this is how my adj therm sw is wired up. I know the sensor's buried beneath the end of a coolant hose (not the hose reducer diag on the right...):-



(Twin wiring to our m100 fans tho'...)

Yep I must confess that I haven't 'milliamped' the battery and disconnected fuses-in-turn yet - as you've advised in an earlier video - to measure the drain. And I'm looking forwards to seeing your proper radio wiring vid after Peter's chewed on it

[peteoddcar]

I understand owners concerns about north facing temp gauge needles, and I am carrying out a bit of development of my own.

I have established that Stoney Racing ( other suppliers too probably) market M14x1.5 fan switches in a wide range of temperatures which includes a 110 - 100 and usefully a 105 - 95.
They also market a 3/8NPT Male to M14x 1.5 female to adapt the switch to M100 thermostat housings.
It’s dual pin, 6.3 spade (not the best but fine for most M100 users ) so it will need a ground link wire to a convenient point and a connector change.
The original switches are quite pricey now, so a tidy alternative is worth looking at.

So I have ordered these parts I’ll get them on next week and follow up on here with the findings.

[peteoddcar]

Correction to the opening post. It’s think it’s the Isuzu Gemini
the ECU came from.

[peteoddcar]

So here’s what I have done so far.

Fan switch and thread adapter from Stoney Racing.
Adapter M14 x 1.5 to 3/8 NPT part no. SRU - TAM14-38NPT £8.25
Fan Switch 105c M14x1.5 part number SRU - TFS -105 £11.95
Plus postage.

I installed with PTFE tape, and the supplied o ring ensuring that there’s no air lock on the face of the sensor by bleeding as the adapter could create an air lock cavity compared to the standard install.
Made a jumper wire spliced into the original connector feed and made a ground link wire worth an eyelet on an adjacent bolt.

I have my thermo couple and meter still installed.

I let the engine run up to temp and cycled the fans a few times to bed the switch and get rid of and air locks
Results
28c ambient ( a couple of weeks ago )
Fan cut in at 104 gauge showing 5/8 dropped out at about 97C gauge on 1/4.
I cycled this a couple of times and the switching temp seemed to be fairly consistent.
I keyed off at the beginning of a ‘fan on’ event, to activate the pump which then ran for about 8 minutes.
With the standard set up in a similar ambient I recall, it ran for about 2-3 minutes.

My switch has a hysteresis of 7C which is perfect. The Stoney Racing spec states 10C which is a bit concerning that the quality may be questionable. These switches do have a tolerance but 3C seems a lot to me. If it were 13C ( 3C the other way ) pump would run for about 15 / mins I’d guess.

This is important for two reasons
1 fans running too long whilst driving
2 pump running too long.

The set up is still on the car I have used it but not been in traffic or deliberately set the fans on.
I’ll leave the set up on the car to get some more experience with it.

My main concerns are around the quality of the switch which appears good but time will tell.

But I think the 105C route might be the compromise some are looking for and a cheaper solution albeit way away from the standard set up and very definitely a modification.
It’s up to you.
There’s a much bigger choice of M14 x 1.5 switches on the market and Stoney Racing do list a 110c so that would be the same as the standard set up.

I may do a plug and play kit if anyone is interested. I could list them on EBay. Just pm me.

[chrism]

As prev mentioned I have an adjustable cooling fan switch and dialling it down to 105C max brings the fans kick-in down to around 1/2 way on my gauge.

Peter's 'electrician' concern with my set-up was with switch reliability plus the 'sealability' of a separate external sensor immersed in a coolant hose connected to a thin wire 'sealed' into a hose connection near the thermostat. So he found components that would give the same effect (of 105C switch-on) but with the same simplicity and reliability of the original (£130+...) Lotus/Isuzu part:-



These were assembled on his SE and we thought they were a sympathetic, respectful upgrade :-



...and his temp gauge gave a fans-on reading around the middle - easing the stress of watching the needle creeping up towards the top :-



Imo this looks like a v-f-m solution that serves to ease stress and reliably replace an expensive/currently out-of-stock/obsolete part. (I reckon it might keep engine temps a little less 'edgy' in our recent hot spells too...)

[peteoddcar]

Thanks for your help Chris
You’ll have to teach me how to upload photos to LEC