Turbo and temperature gauge

[pistonbroke]

Just a couple of completely unrelated questions: 1/ is the turbo operational all the time the engine is running or does it only kick in when under load, accelerating/towing/going up hills etc., and 2/ why does it seem to be felt that the temperature guage in the vehicle needs to be supplemented/replaced by a mason's alarm? In 3 years, I've towed a caravan in summer up hills in heavy stop/start traffic without any worries at all - until I read all the overheating related posts, that is. The guage never goes past 11 o'clock. If I feel the need, I'll put the heaters on full heat and full fan and blow hot air out of the windows. The guage doesn't move down either, so is it working properly?

[francophile1947]

The gauge at 11 o'clock is normal and useless. You won't feel the need to put the heaters on until the gauge goes up, by which time there is a fair chance that your engine is cooked

[dave_aber]

The turbo is driven by the exhaust gasses. Under about 2200rpm, the turbo is just idling round (relatively) slowly, not doing much. At engine speeds above this it starts to spin up to its operational speed (up to 150,000 rpm ), and does its thing.

The standard temperature gauge is deliberately damped so that it will sit at "11 o'clock" all day long. The effect of the damping is that the needle will get to "11 o'clock" earlier than it should, and stay there regardless of what the temperature sender is telling it. It will only move above this position once the engine has already overheated.

A Mason alarm will both un-do this damping to allow the needle to more accurately represent the engine temp, and it will give an audible alarm if a pre-set level is reached.

You can also un-damp the gauge with a couple of resistors for a few pence.

As to why this is the case - Ask Mazda. Presumably they felt that it was right to give drivers the false sense of security of a rock-steady needle rather than letting them actually know what the engine temp was doing.

[pistonbroke]

Thanks guys. What is the point of a guage that doesn't accurately reflect the actual temperature? Why would Ford and/or Mazda fit such a thing?

[Simon Jones]

I think pretty much all cars have have a heavily damped temperature gauge as standard as I've never yet driven a car where you can actually see the effect of the thermostat opening. On our Golf GTi you do not normally see any movement on the gauge, but when the impeller started slipping on the water pump you could clearly see the water temperature going up under acceleration and that was sufficient to show there was a problem with the circulation of the coolant.

Fitting a Mason alarm does allow you to get a lot more feedback about what is going on with the coolant, but I don't suppose Mazda were expecting the Bongo to be more prone to over heating than other vehicle so would not have thought to have done anything other than fit a standard gauge. It's the same instrument panel that they fit to several other models such as the 323.

The other thing to bear in mind is that a number of the overheating incidents are caused by blocked up radiators, thermostats not working, water pumps failing, pipes leaking and failure to flush and replace coolant every two years in line with the manufacturers guidelines. Some of the Bongos are coming up to 17 years old now and that's probably a lot longer than Mazda would have expected them to last.

[pistonbroke]

Thanks for the reply, Simon. But thanks most of all for showing me the correct way to spell 'gauge'. I k new I was wrong when I wrote it. Then I wrote it again,....and again. Plonker!

[Simon Jones]

Auto-correct on the iPad is a wonderful thing

[PaulH]

Regarding the comments about the 'non-moving' temperature gauge, I recently fitted an accurate digital guage - and I can tell you the temperature is going up and down all the time. I suspect Mazda (and most other modern vehicle manufacturers) realised that an accurate gauge was "too much information" and would get loads of enquiries about fluctuating water temperatures. I experience anything between 80 and 103 degrees C. However, I don't mind that - particularly when towing. Having had overheating problems, I like to know exactly what is going on.

[rita]

Regarding the comments about the 'non-moving' temperature gauge, I recently fitted an accurate digital guage - and I can tell you the temperature is going up and down all the time. I suspect Mazda (and most other modern vehicle manufacturers) realised that an accurate gauge was "too much information" and would get loads of enquiries about fluctuating water temperatures. I experience anything between 80 and 103 degrees C. However, I don't mind that - particularly when towing. Having had overheating problems, I like to know exactly what is going on.

Hi Paul,do you have any details of the gauge that you fitted.

[haydn callow]

The TM-2 is extreamly accurate and has a "settable" built in HIGH TEMP alarm.
The temps recorded are very much dependant on where you place the sender sensor

[Northern Bongolow]

if you put your heaters on full blast in an atempt to cool your motor it does not work.
it cools the heater circuit yes---but stops or slows the opening of the thermostat,and stops the cooler rad coolant from mixing/cooling the engine, so is counter productive. best to put your aircon on,as this puts the front rad fans on and cools the entire system when the stat opens. but if the engine is in danger of overheating the fans should already be on .

[Driver+Passengers]

if you put your heaters on full blast in an atempt to cool your motor it does not work.
it cools the heater circuit yes---but stops or slows the opening of the thermostat,and stops the cooler rad coolant from mixing/cooling the engine, so is counter productive.

Very interesting. Cheers.

[dave_aber]

When I had my leaky rad in November, I drove for 200 miles, very gently, with both heaters on full belt to attempt to keep the stat as closed as possible to keep the pressure off the rad. Don't know if the heaters or the gentle driving did the business, but I lost very little coolant on the journey.

I also had the selected ON to keep the main fans running too.

[teenmal]

if you put your heaters on full blast in an atempt to cool your motor it does not work.it cools the heater circuit yes---but stops or slows the opening of the thermostat,and stops the cooler rad coolant from mixing/cooling the engine, so is counter productive. best to put your aircon on,as this puts the front rad fans on and cools the entire system when the stat opens. but if the engine is in danger of overheating the fans should already be on .

Never heard of this before.

[dave_aber]

It doesn't cool the motor because the thermostat is doing what is is intended to - keeping a static thermo. The heaters will remove the heat, and the radiator will remove less heat (or none) - hence the temp will stay in the control range and be (approximately) static.

maybe more accurate to say it does cool the motor instead of the radiator doing it, but it won't make the motor run any colder.