How "HOT" does it have to get ???

[Hippotastic]

Hi Guys,
Mazda and other Japanese car manufacturers doctored temperature gauges by fitting a Zener diode.
By removing the Zener and a resistor,and fitting 2No resistors the gauge will work as it should.

Cost of resistors about £1.00.

Malc..

Sounds like a fact sheet to me....

[haydn callow]

well after reading this thread with interest, i spoke with my mechanic bro in law yesterday about the high temperatures etc and the muffling of the temp gauge

his reply was, has any one considered sticking a 80 deg,s stat in

all i could say was ,, i dont know lol ,, i will ask

at least the stat would open at 80 degs and stay cooler

should solve most probs with some bongo,s running hotter than others

im no expert , but just passing on information that may be some use,,,,,

so dont stone me

i will give you my mechanics address and you can all attack him



andy

Yes the stat would open sooner...but once open the temp would do the same as after a 88 degrees stat opened....the high temps attained at engine "hot spots" would not alter.

[Mr Halibut]

But aren't these observations all a bit unscientific. How do we know what temperature at various points in the engine/exhaust system equates to the engine core 'going critical'? Taking it to the extreme, if you attached the temp. sensor to the exhaust manifold, you'd wonder from the temp. readout why the oil was'nt boiling, never mind the coolant.

Or have I missed something (probably, knowing me ). But I must admit, trying to work out exactly what the Bongo temp. gauge (and other cars too no doubt) is there to do does remain bit of a mystery.

I think you are spot on Mike....when I had the sensor on the inlet side under a rocker cover bolt the gauge never went above 96C towing on a hot day. The big differance in the Metal Temp at various spots on the cylinder head must cause stresses and strains which over time could lead to weaknesses. I just pointed this out co's I was suprised at such a high temp at point subject to watercooling.

I have an ebay temp guage in a similar position and towing up a hill will cause the guage to overscale (the advert said max 120degC although it overscales at 110.9DegC), this made me worry to begin with but it hasn't gone critical yet... My assumption is the close proximity to the exhaust manifold is making that area a lot hotter than where the actual temperature guage is located. I keep meaning to pop the sensor somewhere on the other side of the engine to test it but every time I look at that side of the engine theres so many pipes/brackets/doodars etc.. that I give up and leave it where it is.

[dandywarhol]

well after reading this thread with interest, i spoke with my mechanic bro in law yesterday about the high temperatures etc and the muffling of the temp gauge

his reply was, has any one considered sticking a 80 deg,s stat in

all i could say was ,, i dont know lol ,, i will ask

at least the stat would open at 80 degs and stay cooler

should solve most probs with some bongo,s running hotter than others

im no expert , but just passing on information that may be some use,,,,,

so dont stone me

i will give you my mechanics address and you can all attack him



andy

The Bongo one DOES open at 80 Forget the stones -

[patnben]

About 4 years ago, I modified the gauge components to get rid of the dead zone
after the top of the radiator split without warning, except for a cloud of steam.
I immediately looked at the temperature gauge and it was still reading normally.
Luckily, I was pulling into a car park at the time and I had the engine switched
off in a few seconds and I doubt if the engine had suffered excess temperature.

After I modified it, I no longer had the dead zone and the range was good enough
for me and normal running temperature showed around 12 o'clock. Testing with a
surface thermometer showed that the gauge was reasonably linear over the scale
which is about 50 - 130 Celsius. At the time, I had no information on the sensor
curve and was therefore working relatively blind.

I was fairly happy with this for a couple of years or so; except when I'm driving
I spend most of my time looking at the road ahead and not at the instrument panel.
What I needed was a loud warning device and considered adding one to the existing
scheme. Due to the Bongo's age (1996) and signs of corrosion, - but low mileage -
I bought a 2000 model and kept the old one for emergencies.

Around this time Haydn had produced his low level alarm, so, as I don't believe in
re-inventing wheels, I had one fitted at a Bongo bash which does a good job and I
am happy with this. I also fitted the Mason alarm which; while not as good as my
original modification on the old Bongo; gave me a lot more confidence in warning
me of any potential overheating problems.

Due to clearance issues in multi story car parks, I bought a 2000 2WD tin top to
use as our daily transport, usually a shopping trolley and golf cart, which the wife
uses. Due to unfortunate circumstances, it is necessary that I use the 2WD tin top
to tow my caravan now; and it has no overheating protection. I recently purchased
Haydn's TM2 combination alarm system which was simple to fit and appears to work
extremely well as you would expect, although I have yet to tow the caravan.

The whole point of all this extraneous waffle is that I just can't bear to look at
the dysfunctional Mazda gauge, I simply have to do something about it for no other
reason than my own sanity. As I intend to remove the instrument panel to replace the
speedometer face plate; I shall modify the temperature gauge at the same time.

If anyone else is interested in doing this mod; I will detail the methods and take some
photographs, if not, I will simply do the job and forget about it as I don't intend to do
any more.

[haydn callow]

Ben... if you put the temp alarm sensor as per the photo in the instructions (threaded hole on exaust side) you will probably have to reset the TM-2 whilst towing.
I didn't and when I pulled the C'van this weekend it scared me to death when it went off at 105C......(never gone off at that setting solo)......It actually reached 123C but no worries as this area is close to the exaust. This position may not be the best if a lot of towing is happening. I only recently moved the sensor to this position, before it was under a "rocker" cover bolt on the inlet side and the reading when towing a max of 102C.
Bid differance in temp around the cylinder head. (to be expected I suppose)

[patnben]

Thanks for that Haydn, I had already anticipated the difference and in my
usual overkill manner, I temporarily fitted 3 PT100s, front and rear on
the exhaust side, and one on the inlet side glued close to the temperature
thermistor. This allowed me to measure conditions while actually driving.

We have a long steep hill close by so I was able to give it some welly for
enough time to see the difference in temperatures. As expected - due to
localised heating of the exhaust gases - there was a differential of about
10 - 12 degrees when I finally reached the top of the hill. When travelling
on a level road at around 40 MPH and a very light foot on the go pedal,
the differential was less than 2 degrees. As I am more interested in the
water temperature, I have fitted the TM2 thermistor on the inlet side.

Sad as it may seem, I am getting more exited about the trip to the "Southern
Softies" than the actual pleasure of the event.

Ben.

[haydn callow]

It's a age thing.....dosn't take much these days to get excited.

[patnben]

It's a age thing.....dosn't take much these days to get excited.

At my age, there's not much else to get exited about.

[francophile1947]

Definitely be interested in your mod Ben

[New Forest Terrier]

I have just got the low coolant plus temperature alarm with the digital readout and find it shows very clearly when the thermostat opens.The temperature climbs slowly to 87 and then the stat opens and it levels off or falls to 86 and stays round there except for traffic ques or motorways.

Could this be a help in bleeding the coolant system. The flatening off is so obvious there is no doubt that the stat has opened.

Im not greatly techie so do not all jump on me from a great height at once

[Grahame at work]

Just thought I’d add my few pennies worth.

A little before Christmas I fitted a digital analogue look-alike meter and interface I had designed to monitor the coolant temperature as the ECU sees it. This meter is a 17 segment LCD that looks like an analogue meter and the interface connects in parallel to the 2 terminal temperature sensor above the starter motor feeding the ECU.
As some of you know I had been monitoring the ECU coolant temperature sensor with multi-meters for some time and had got a reasonable understanding of the variations of temperature. However, the sensor is non-linear and I had only the workshop manual to give me an estimate of top end calibration based on when the radiator fans come on. I could only get a measurement for when the low speed fans come on, I really wanted a measurement when the fans went to high speed but I could never get them to come on – and I really tried hard.
So I gave up and designed and calibrated my interface according to my ‘best guess’ from the data I had up to that time. I set the meter to read (estimated) from 86C to 110C in 1.5C steps. This being from just above the stat opening temperature to just above when the fan goes to high speed – panic level.
When fitted and run for a few days I was rather chuffed to see that the temperature sat at 50%, mid-way, straight vertical position for most of the time (estimated 98C), driving on the level no matter what speed. It drifted up and down according to the hills and traffic conditions. The low speed fans coming on above 2 segments above 50% and off again below 2 segments below 50% ~ on = 101C off = 95C. The hottest I got it to was 4 segments above 50% estimated at 104C at which point the Mason gauge was showing about 90% of full scale and the alarm was just beginning to sound.

I should point out (although obvious to most I suppose) that this is the temperature about 2/3 rds up the block and will be lower than the temperature measured at the top front end of the head which is where the dash gauge sensor is.
My theory: -
So if the stat 'normally' runs mid-way at 90C, the ECU sensor is at 98C the outlet temperature to the bypass and radiator should be up at about 102C so you need about 20C of cooling via the radiator (and pipes) to maintain the stat at 90C assuming that the bypass and radiator flow at the point of mixing is 50/50. This accords with my measurements of hose temperautres either side of the radiator.

I was going to try recording the temperature along side the thermocouple reading from the stat housing on the Maplin trip recorder sat above my left shoulder to also catch the rev counter in view. BUT as some of you may be aware my Bongo was written off a few weeks ago and my meter and interface are now in a pile of bits in a bag.

When I get a new Bongo I’ll be re-fitting it and starting again.

Regards Grahame

[jone_it]

Standard gauge is not THAT useless... Once it did save life of my engine after incomplete radiator bleeding. That was the only time I watched it in real action but since do wish to never see it again!

[mikeonb4c]

Standard gauge is not THAT useless... Once it did save life of my engine after incomplete radiator bleeding. That was the only time I watched it in real action but since do wish to never see it again!

Good to hear from you jone_it - where have you been.

Whilst on the subject, where is Peg Leg Pete these days - not heard a peep out of him for some time.

[Roberus]

....excuse me for being thick....it's been a long day....have finally picked Bongo up complete with LCA/TM2 fitted. What sort of temperature should I expect in normal running?

Up a steep incline on the A380 (good old Telegraph Hill) she was reading about 110 (buzzer went off at 105)...is this normal or is it set too low etc etc....sorry but I really am dog tired!! Zzzzzzzzzzzz!!!

Thanks in advance for replies and be gentle with me!!

Cheers

Rob