Cold Weather Running

[middie]

Hi Guy's

In this cold weather my Prius engine cuts in and seems to run fast as though it is on choke ? It must have some sort of cold start enrichment device fitted i suppose. The consumption in town has dropped to 32/33 mpg. The consumption display goes between 7 mpg upto 99 mpg then back again,

Before i contact the dealer has anyone got any ideas as to what is causing it. Apart from that the engine is not missing a beat.

[Aimhigh]

I have a similar experience (less so the racing) but certainly more use of the engine and consequently an increase in fuel consumption. Only forcing ev mode reversed that.

I suspect that there are a couple of things happening, the easiest to eliminate is the heater !

But welcome more seasoned Prius owners experiences.

R

[Chris Dance]

My consumption recorded over 100 miles mainly town running 54.9 to gallon. The engine does increase revs on start but not excessively. 32-33 MPG seems very low to me.

My son is in the French Alps, temp is -10 degrees. I have just asked about his prius fuel consumption it is 52 MPG.

[timberwolf]

I think there are going to be a lot of variables that determine the sort of mpg someone gets.

When, where and how?

When is the vehicle being used? If you starting a journey early, say 5:30am, on a frosty winters morning, you can spend 5 or 10 minutes scraping the ice off the car. People who don't start driving until after 9:00am often don't appreciate the huge difference that makes when a car is kept outside, especially if when they get up the sun has melted most of the ice .

Where is the car kept, in a garage or outside?

What distance is being travelled? For example, a short journey of only a couple of miles is most likely going to an mpg killer during the winter, as the engine will probably not have warmed up in that time.

How is the car driven? What was the mpg like when the weather was warmer?

I've not had my Prius long enough to offer any personal experience, but my engine does seem louder during this very recent cold snap.

When I was being given the orientation of the controls by the dealer, it was pointed out and demostrated to me that use of the front demisters will keep the engine running.

The American's recommend using the A/C AUTO setting, it apparently can work better than trying to control things manual and can reduce how often you need to use the front demister.

[GreenJuice]

This appears to me to be 'normal' Prius behaviour. The onboard computer will run the engine a bit extra in certain situations, among them being when warming from cold and when the Battery charge is getting low. When warming from cold, this applies to warming the engine as well as warming the interior.

As temperatures have started falling, I've been following various websites and testing techniques for ensuring the engine shuts off when I lift my foot off the accelerator, apart from using the EV button. Some of this information might allow you to take more control of our Prius and increase your options for improving fuel efficiency even more.

You may already be aware that there are several consecutive stages of Prius engine warm-up, called S1 to S4 on various websites. S4 is the engine's fully warmed state. S1 is a very brief early stage which only lasts about a minute after starting, so most of the peculiar engine behaviour you are experiencing are in the S2 and S3 intermediate stages of engine warm-up.

During S2, if you are not 'demanding' energy from the engine to warm the car's interior (either manually or A/C AUTO), the engine will shut off as soon as you take your foot off the accelerator pedel (and therefore remain off when you are stationary). You can put this to a simple test when stopped at a junction or in traffic in the early stages of engine warm-up. Turn off the car's interior fan in the Climate display and your engine should cut out. Turn on the fan again and the engine will race on again almost immediately. It is being asked to warm the interior whilst still cold itself.

In S4, turning on the interior fan should not cause the engine to come on. Therefore, the more fuel efficient time to warm the passenger cabin is after the engine is fully warmed in S4.

S3 is an even more peculiar intermediate stage of engine warm up. The engine is warmer than at S2, and actually at the same temperature as required for S4, but it will refuse to shut off when you lift your foot off the accelerator. This is therefore a fuel inefficient situation to be in, and most websites advise that you should try and 'force' it into S4 at the earliest opportunity. It appears that there may be only one way to do this, which is to come to a complete stop (and you will hear the engine still running) and wait for up to 3 to 7 seconds, after which the engine will shut down. As soon as this happens, the engine has switched to S4 - the most fuel efficient stage of operation (you need to have EV mode off for this trigger to switch to S4 to work). You can then drive off and from that time be free of any more peculiar warm-up behaviour!

You can find more information on S1 - S4 here. Be prepared that there is some tough reading and it took me a while to digest all this material. Hope you find it helpful!

[GreenJuice]

Apologies that link didn't seem to work.

Here is another in full: http://priuschat.com/forums/knowledge-base...erence-aid.html

and as a link

[benw123]

Hi all, newbie to the forum here. Nice to find some Prius content that's UK-based, as opposed to PriusChat over in the States!

Regarding cold weather running, I've recently blocked the upper part of my Prius' grill using pipe insulation, as directed by some threads PriusChat. I'm seeing a 2mpg improvement (from 50 to 52mpg). It's a 10-minute job and perfectly safe as the upper grill is well away from the engine and the radiator. The benefits are supposedly two-fold; that the blocked grill improves aerodynamics slightly and keeps the engine warmer, which should in theory stop it kicking in when it gets too cold.

Anyone else blocked their grill on here?

[Chris Ray]

That sounds a good thing! I have seen my consumption drop to 49-50 recently, when it has been an average of 55 the last 8 months.

Could you provide a bit more detail about what you did?

Thanks

[GreenJuice]

That sounds a good thing! I have seen my consumption drop to 49-50 recently, when it has been an average of 55 the last 8 months.

Could you provide a bit more detail about what you did?

Thanks

I decided to fully embrace the methods on priuschat.com by blocking both upper and lower grills with pipe insulation (just a few quid from Homebase, cut to fit and push-fitted into place. There are several example photos posted on that website, but unfortunately its a little harder to post a picture on this one.

I monitor temperatures using ScanGauge and can agree with the observations made by others that blocking all grills does not seem to be a problem whilst ambient temperatures are below 10 C (50s F), either in long urban start-stop traffic or long Motorway runs.

When temperatures were at 15 C, I had one episode when the cooling fan/pump came on (engine temp was 90+ C). This was effective in cooling the engine within seconds, but was of course fuel inefficient, so I started removing one central part of the lower grill block if I anticipated a long journey at these or higher ambient temperatures.

If you are adjusting your driving to maximise fuel economy (and therefore minimising engine use), there is no doubt that grill blocking does help to get the car up to operating temperatures and also importantly to keep it there. I believe you will get a measurable improvement in mpg, although there are probably many other more important factors that will influence it.

[Chris Ray]

Thanks Greenjuice, must give that a go!

Used to have an old Citreon GSA which was air cooled, and in the winter, you were supplied with a plastic insert to cover the grille, with no ill effects, so cannot see any problems with the insulation idea.

[benw123]

I decided to fully embrace the methods on priuschat.com by blocking both upper and lower grills with pipe insulation (just a few quid from Homebase, cut to fit and push-fitted into place. There are several example photos posted on that website, but unfortunately its a little harder to post a picture on this one.

I monitor temperatures using ScanGauge and can agree with the observations made by others that blocking all grills does not seem to be a problem whilst ambient temperatures are below 10 C (50s F), either in long urban start-stop traffic or long Motorway runs.

When temperatures were at 15 C, I had one episode when the cooling fan/pump came on (engine temp was 90+ C). This was effective in cooling the engine within seconds, but was of course fuel inefficient, so I started removing one central part of the lower grill block if I anticipated a long journey at these or higher ambient temperatures.

If you are adjusting your driving to maximise fuel economy (and therefore minimising engine use), there is no doubt that grill blocking does help to get the car up to operating temperatures and also importantly to keep it there. I believe you will get a measurable improvement in mpg, although there are probably many other more important factors that will influence it.

That sums it up perfectly. I don't have ScanGauge but the engine must be warming up more quickly, because after setting off in the cold it switches itself off when the car has stopped, as opposed to running continually. The 2mpg improvement I saw is modest, but given that a 5-pack of pipe insulation costs just £3.00 from Homebase, the outlay is barely worth mentioning.

Here's a picture of my blocked upper grill:

The pipe insulation is cut through one side (so you can wrap it over a pipe) and this allows it to be compressed. The side that is cut should be placed nearest the engine, and you have to force the insulation in - the compression holds it in place. I went a stage further and cut slits into the insulation. This is because inside the grill are about 5 thin vertical supports, and the slits allows the insulation to pass further into these. You'll understand when you come to do it yourself!

[fuel miser]

Whilst I've been in Cumbria over Xmas and the New Year, I've seen the temperature gauge on the car reading as low as minus 9 deg. C. I notice the engine running much more, especially in traffic when it should be fully warmed up. Today I bought a roll of loft insulation, currently on sale at B&Q for £5. I removed the plastic panel at the very front of the engine bay (by the bonnet release catch). It's held in by six studs and is quite an easy task. I tore off pieces of the roll and stuffed it into the cavity to the front of the radiator, until the gap between the radiator and both upper and lower grilles was completely filled. I used only about 25% of the roll so it will last four years i.e. £1:25 per year! This should surely serve the purpose just as well?

[benw123]

Whilst I've been in Cumbria over Xmas and the New Year, I've seen the temperature gauge on the car reading as low as minus 9 deg. C. I notice the engine running much more, especially in traffic when it should be fully warmed up. Today I bought a roll of loft insulation, currently on sale at B&Q for £5. I removed the plastic panel at the very front of the engine bay (by the bonnet release catch). It's held in by six studs and is quite an easy task. I tore off pieces of the roll and stuffed it into the cavity to the front of the radiator, until the gap between the radiator and both upper and lower grilles was completely filled. I used only about 25% of the roll so it will last four years i.e. £1:25 per year! This should surely serve the purpose just as well?

It should do, but I'd worry about the insulation being inside the engine bay. I'm sure that it's fire-proof, but there is also the danger of the insulation getting dragged into moving parts, no matter how well it's secured. The other advantage of the pipe insulation is that because it's on the outside, the air flow is directed over the bonnet, rather than allowing a small pocket of air to become trapped in front of it.

[JonFB]

The other advantage of the pipe insulation is that because its on the outside, the air flow is directed over the bonnet, rather than allowing a small pocket of air to become trapped in front of it.

..however the other disadvantage of the pipe insulation on the outside is that it looks bl00dy rediculous! Sorry but it does, I know the Prius is hadrly a work of art but come on, all for 2 pathetic mpgs?

[benw123]

The other advantage of the pipe insulation is that because its on the outside, the air flow is directed over the bonnet, rather than allowing a small pocket of air to become trapped in front of it.

..however the other disadvantage of the pipe insulation on the outside is that it looks bl00dy rediculous! Sorry but it does, I know the Prius is hadrly a work of art but come on, all for 2 pathetic mpgs?

To be fair, the picture I took is a close-up. From a short distance it's not really noticeable, but since I'm doing a minimum of 270 miles a week in it, anything I can do to boost the economy is going to help me. Besides which, that's what the car is about - fuel economy. It's no different to cutting a hole in the front bumper in a high-performance car to let more air in!

Back on topic, after washing my Prius in the bitter cold on Sunday, I also checked the tyre pressures. I had put them up to 35PSI all round, but they'd dropped to 30PSI, so I pushed them back up again. Higher tyre pressures means better economy too, but don't go too high as the contact patch on the road gets smaller which in winter is a tad risky. I know some owners on PriusChat run in excess of 40PSI which is too much in this kind of weather I think.