Cold Idling

[RavmanDave]

My 2007 4.3 D4D Rav has always had a 750rpm speed at tickover whether hot or cold. In the last couple of days however, when the weather has been exceptionally cold, the idling speed at start-up has been around 1200rpm and has remained so even when the engine gauge has shown normal running temperature. I have not been on a drive of more than about 15 minutes and have tried switching off things such as heater fan, headlights etc to no avail. Is this normal or should I get Mr T to investgate?

[dave.m]

When the outside temp gets to a certain low, the ECU increases the idle speed in anticipation of you using the heater and

de-mister etc. Its to take the pressure off the Battery and is quite normal.

[Mereside]

Hi,

If its any help my T180 has been idling at a similar speed but eventually after a good run slows down. I thought something may be amiss but when the weather warmed it slowed down again. Nothing to worry about at this time.

Regards

[Davrav]

My 2007 4.3 D4D Rav has always had a 750rpm speed at tickover whether hot or cold. In the last couple of days however, when the weather has been exceptionally cold, the idling speed at start-up has been around 1200rpm and has remained so even when the engine gauge has shown normal running temperature. I have not been on a drive of more than about 15 minutes and have tried switching off things such as heater fan, headlights etc to no avail. Is this normal or should I get Mr T to investgate?

Hi Dave,

My 2008 4.3 D4D has been doing exactly the same - I have assumed it is a 'Very cold start' feature that helps the engine to warm up quicker.

I have also noticed a considerable drop in MPG during the recent cold snap. Did enquire of 'Honest John' [Times online motoring chap] about screening part of the front grille to help keep engine temp up but he did not recommend it [though didn't give a reason]. He recommended either a block heater at a cost of about £500.

I have also read about a coolant additive called Motomax [i think] at about £16 a tin [two needed].

I will be interested to see responses to your question and would be grateful to hear from anyone who uses an additive or who screens their grille.

David

[Dippy]

My 2008 4.3 D4D has been doing exactly the same - I have assumed it is a 'Very cold start' feature that helps the engine to warm up quicker.

I have also noticed a considerable drop in MPG during the recent cold snap.

Interesting, when I remember how the drivers of turbo'd petrol cars look forward to cold days as it apparently makes the turbocharging more efficient!

[anchorman]

Modern lubricants and coolants have all the additives they need. Additionally they will not have been tested by the manufaturer. An example of this is brake cleaner - an aerosol product available for the cleaning of brakes and friction materials. In fact when I worked for Ferodo we absolutely forbade the use of these products as they attack the resin binder system in the friction material. There isn't one supplier of those produscts that has the blessing of a friction material manufacturer but the companies sell truck loads of the stuff to unsuspecting users. I strongly suspect you will get a similar response from oil and coolant manufacturers - if it would benefit from being in, they would have put it in.

Your radiator is affectively closed off automatically. The thermostat in the engine prevents any coolant from circualating through it until it has reached 88C. The only route for pumped coolant until that time is around the cylinder block and through the heater matrix. Unfortunately, a disadvantage of a modern diesel engine is that it has a high thermal efficiency and the warm up period is rather prolonged. To help with this your diesel RAV (But not petrols) is fitted with an electric heater element which is automatically switched on during the initial warm up period. In fact when you first start your car it will still feel freezing cold despite the element being active but the element is only really capable of raising the temp inside the heater to prevent frosting of the glass during demisting - particularly as this will be done (unless forced manually) with the aircon active. This is because conditioned air has had the moisture removed.

I would fight shy of additives and mods to the airflow at the radiator. Remember when the temperature is up to normal the vehicle will engage 2 high powered fans to expell unwanted hot air that would otherwise cause overheating and it doesn't want any blinds in the way thank you very much!

Be patient with the heating and cooling system - a lot of thought and development cost has gone into getting it to getting the best compromise. If you have an automatic heater (climate control) set your desired temperature and avoid fiddling with it when the vehicle is warming up. It is controlled by a sensitve computer aided system that knows full well that trying to turn the fan up will actually cool the interior. It has been programed to bring the interior to the set temperature as quick as is physically possible - human interferance cannot beat it (although my wife and daughter will rutinely despute that and convert it into a supercooled freezer on the way to the supermarket in a frenzy of random button pushing).

If you are dead set on making an improvement then you have to look at some external method of forced pre-heating. This can take the form of a combustion heater or a plug in block/interior heater or even the electric fan solution invented by the very clever professor shcm.

Any of these mods is going to cost you in terms of installation and running costs. Easiest solution is to walk out to the car 3 minutes earlied on a frosty day!!!

[Davrav]

Thanks for the comprehensive explanation Anchorman.

You have confirmed what I was suspecting. I guess I have been spoiled a bit by my previous ride [bMW E39 petrol mobile armchair]

Trouble was, I couldn't see over the hedges in that!