heated throttle body

1996 4.6 V8 gems

why is the throttle body heated? i would have thought it better to keap the incoming air as cool as poss! i heard of a mod to give more responsiveness by bypassing the throttle body, diverting the hot coolant and cool the inlet air temp a little! i tried this as i had plenum of the other day, havent noticed a difference apart from hot starting isnt as "crisp" as it was! cant see how a heated throttle body would help hot starting? anyone know whats going on down there?

We have an echo...

If you check out the RPi Engineering pages it explains it a bit better. The only conclusion that I've drawn is that it's the weakspot that blows when your thermostat is goosed.

Take5 said:

We have an echo...

If you check out the RPi Engineering pages it explains it a bit better. The only conclusion that I've drawn is that it's the weakspot that blows when your thermostat is goosed.

Click to expand...

weakspot, thermostat?
i found it on rave (my index dont come up making it dificult to find anything) its to stop the throttle body from freezing up in extreme cold weather conditions, i would guess prob not needed in the UK!

redrange said:

1996 4.6 V8 gems

why is the throttle body heated? i would have thought it better to keap the incoming air as cool as poss! i heard of a mod to give more responsiveness by bypassing the throttle body, diverting the hot coolant and cool the inlet air temp a little! i tried this as i had plenum of the other day, havent noticed a difference apart from hot starting isnt as "crisp" as it was! cant see how a heated throttle body would help hot starting? anyone know whats going on down there?

Click to expand...

Hello Red,

As far as I know, this feature first appeared on the Rover SD1 Efi Vitesse in 1982 and was subsequently on all Efi SD1's until production ceased in 1986. thereafter it appears on many if not all Efi Rover V8's

This is my personal theory supported by a scientific explanation.

This plenum heater block business! Why did Rover do it? Its not explained anywhere that I have seen so I thought about it and its probably down to basic science!

I think its an aid to efficient accelerating directly from idle, when very cold, without hesitation.

Think about it this way? Its a normal cold winter morning - maybe even freezing!

Start the car and the cold start injector may or may not be needed. It ceases after cranking ends anyway.

The Efi system adjusts mixture for coolant temperature and continues to do so until it gets hot.

At this time the fuel/air mixtures are quite rich and some pretty inefficient atomisation is going on - methinks!.

The EAV raises idle speed and gradually reduces it until it get hot.

The coolant in the engine block galleries starts to warm up straight away, and is immediately driven round the plenum heater block by the water pump, bypassing the coolant system thermostat.

The inlet tunnel(s) start to warm up and the small amount of air resident in the inlet tunnel(s) also gets warm.

Hardly any air passes by the disc(s) of course so the air flow is very low because nearly all the idle air is taking a different route.

Now you hit the loud pedal and the throttle is open.

The injectors fire and lots of bang juice is suddenly available, plus the first whiff of air is comparitively warm, considerably aiding fuel atomisation.

The first few bangs are therefor much more efficient and the car launches without hesitation.

So there is no launch flat spot and once the car is off and running - who cares?

Some people disconnect the heater pipes to the plenum, but in this case the plenum intake tunnel walls now stay cold(er) (at this early morning time) and when you hit the loud pedal you get, no warm air, poorer fuel atomisation, inefficient combustion and a possible flat spot at launch.

Rover must have had a reason for doing it - and this is just my private theory.

It seems illogical to me that a car that is supposed to impress with its "get up and go" would be without a system that helps to achieve that goal in all conditions.

But then again the original system design was for a road-going executive saloon (Vitesse or VDP Efi) where the posh owner/drivers would be thoroughly disgusted with a flat spot at launch on a cold morning and complain bitterly to the franchised seller. QED

Like I said - just a theory - but it has the merit of logic as opposed to hearsay.

There is disagreement by others who say it is just for deicing when cold, but I would like to see their explanation of the science, because its only cold air being heated.

Despite my theory I have an open mind on the subject so if anyone in the RR community can point me toward a Rover explanation I would be very pleased to see it.

Do you know of a documented Rover explanation?

interesting points raised there, i have bypassed mine now and ill see how it goes, the weather is currently warm here so may have to wait to see whats going to happen in colder conditions!
watch this space!

Hello Red,

I have some other inputs from several quarters who say it was an icing thing and one from a club member who said his had been bypassed for ages and he had not noticed any difference in cold weather.

I turns out that it had been bypassed since he owned the car and he was comparing it to a prior vehicle. DOH!

To my mind the telling part of my analysis is:

"once the car is off and running - who cares?"

And with regard to removing it in summer you are right it would be impossible to tell, so I think the only way to analyse it would be to change the bypass on successive similar winter days (or for a period midwinter weeks even) and try to detect the difference that way.

Seriously though - If someone could point to a Rover document or tech bulletin (they issued hundreds) that gives the reason for the heated plenum zone it would put all the theories and urban myths to bed once and for all.

On all the SD1 documents I have seen there is no reference to the "reason".

Ramon