I have a peugeot partner escapade. It doesn't have an external temp thermometer and I'm thinking to install one. Where do they usually position the sensor bulb on the car, to measure air temperature it has to be positioned so that it is shielded from direct sunlight, have exposure to clean air so to speak, and not be exposed to engine heat. Any tips or ideas?
Don
Under the front bumper is the usual place, though my manufacturers built in one suggests the make some sort of compensation to the figure displayed. What ever, it seems pretty accurate, with no variation even when stood in traffic.
plastic things which probably suck in solar radiation like sponges. Perhaps I should cover them with aluminised polyester :-) . Don
A common place is just behind the front bumper in the wheel well protected by the liner.
I mounted the sensor of mine below the driver's mirror. Ran the cable through the door under the hinge and under the footwellmat. Despite the door being opened and closed around twice a day for 5 years, the cable never failed. The sensor fell off once when the double-sided sticky tape failed, but I stuck it back on with some silicone cement.
Some Pugs have the sensor in the underside edge of the door mirror.
Bob
Mine's in the radiator grill, well in front of the radiator itself.
BTW, many cars may not have a specific sensor. The inlet air temperature is measured by the fuel injection system, and you could use that value to drive a low temperature warning.
Vauxhall's(well astra's) its fitted to the front bumper on the bottom as far back as it will go facing the ground, it does pick up the heat from the road
"Donwill" gurgled happily, sounding much like they were saying:
Underside of one door mirror's the usual place, or under the front bumper.
The former can be subject to heat-soak when parked, especially on a dark coloured car, the latter can get a bit chilled on cold wet days or soak from the rad in heavy traffic.
My old Renaut had it under the drivers wing mirror. It actually looked like the paint had run and collected there in a big drip. In fact the kids tried to pick it off one day when they were washing the car!!!
I dont think that would give a true value ambient value as the venturi effect will change the temperature(cant remember which way)
You could well be right. But I think/thought some early examples of these did exactly that - meaning no requirement for anything extra under the bonnet (or door mirror!) but giving the driver some impression of external temperature as a benefit of the inherent working of the engine management system. Albeit inaccurate.
Do you know of one where this is actually the case? That sensor is only interested in temperature change rather than absolute values.
Kevin gurgled happily, sounding much like they were saying:
Depends on where it is, and on the conditions.
Once the engine & engine bay are good and hot, it'll be warmer than ambient. Same on a turbocharged engine, if the sensor's looking at the compressed air, which it'd need to, since it's the temperature as it reaches the engine that matters.
OTOH, carb icing is a fine practical demonstration of the venturi effect cooling the air down markedly.
Anyway - most cars don't have an inlet air temp sensor these days - they measure the mass of the incoming air instead via an air mass meter rather than air flow meter plus inlet air temp.
Depends where the sensor is and how the FI works.
Have installed both Megasquirt and Omex ECUs in the recent past, I can assure you that both these systems have inlet air temperature sensors. You need them for cold start enrichment, for one thing. (And the Omex on my TVR doesn't have an air mass meter, either - it does fuelling solely on throttle position and lambda.)
Nope.
It needs to know the absolute temperature for cold start enrichment.
Huge gurgled happily, sounding much like they were saying:
Yes, they do. MS is very low-tech by modern standards. I know nothing about the Omex system.
Besides, coolant temp sensors'd normally be used for the cold-start enrichment.
I presume it also has a coolant temperature sensor - and it's that one which does most of the work. The air temp one just for fine tuning.
Pretty crude, then?
As I said normally the coolant sensor for this. If you think about it that tells the temperature of the actual engine which effects the mixture requirements - not the air temp one which shouldn't really sense engine temp at all. After all you don't need choke on a hot engine on a cold day. ;-)
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