Fuel Tank Reserve

[Danlo]

Anyone seeing a ridiculously large fuel reserve in their RAV4 PHEV? I filled up my 2023 RAV4 PHEV the other day when I had about 60 miles shown on the distance to empty display. At my current fuel economy (~40mpg), that would suggest I had 6-7 litres left in the tank (not counting any reserve). When I filled up at the petrol station, it clicked off at just over 32 litres and the fuel gauge in the car showed 100%. This would suggest there is a reserve in the tank of 15 litres, which out of a 55 litre tank represents over 27% of the entire tank as a reserve. I've read that Toyota are generous with the fuel reserve but 27% seems mind blowing to me.

[FROSTYBALLS]

Yes, Toyota tends to allow a generous reserve. If you run out of fuel in a hybrid, you can cause damage to the hybrid system, and this won't be covered under warranty.

Check the owners manual - warning lights, and low fuel light. That usually provides the reserve in litres.

[kucyk]

1 hour ago, Danlo said:

Anyone seeing a ridiculously large fuel reserve in their RAV4 PHEV? I filled up my 2023 RAV4 PHEV the other day when I had about 60 miles shown on the distance to empty display. At my current fuel economy (~40mpg), that would suggest I had 6-7 litres left in the tank (not counting any reserve). When I filled up at the petrol station, it clicked off at just over 32 litres and the fuel gauge in the car showed 100%. This would suggest there is a reserve in the tank of 15 litres, which out of a 55 litre tank represents over 27% of the entire tank as a reserve. I've read that Toyota are generous with the fuel reserve but 27% seems mind blowing to me.

It's not about a reserve being big, somehow the car is miscalculating the HV distance in PHEV. I don't know what triggers it, but there's a definite glitch causing extremely low HV distance readings even with a half full fuel tank. It seems that the HV range is dropping even if you do 100% EV driving.

[Danlo]

2 hours ago, FROSTYBALLS said:

Yes, Toyota tends to allow a generous reserve. If you run out of fuel in a hybrid, you can cause damage to the hybrid system, and this won't be covered under warranty.

Check the owners manual - warning lights, and low fuel light. That usually provides the reserve in litres.

Thanks, I shall read the manual again, must have glossed over that part. However, 15 litre reserve seems crazy even if it's to protect the hybrid system. That reserve is the equivalent of around 130 miles at my current fuel economy 😮

[Danlo]

2 hours ago, kucyk said:

It's not about a reserve being big, somehow the car is miscalculating the HV distance in PHEV. I don't know what triggers it, but there's a definite glitch causing extremely low HV distance readings even with a half full fuel tank. It seems that the HV range is dropping even if you do 100% EV driving.

I can's say I've noticed that behaviour but I'll keep a closer eye on it. When the tank is full, the range shows about 500 mile and when I was down at 60 miles left the gauge showed roughly just under an 1/8th of a tank remaining. Definitely not getting 500 miles out of a full tank, so you could be correct about the miscalculations.

[kucyk]

3 minutes ago, Danlo said:

I can's say I've noticed that behaviour but I'll keep a closer eye on it. When the tank is full, the range shows about 500 mile and when I was down at 60 miles left the gauge showed roughly just under an 1/8th of a tank remaining. Definitely not getting 500 miles out of a full tank, so you could be correct about the miscalculations.

It's miscalculating for sure. You start with 500 HV distance, drive on EV only, HV drops to 450, you charge the car but HV never recovers back to 500.

[Flatcoat]

The HV range is simply a forecast figure based on recent driving habits and fuel usage. How can it calculate what you haven’t yet driven? To rely on it as gospel is foolish. The only figures that matter is the actual amount of fuel used over a given distance. 

[kucyk]

1 hour ago, Flatcoat said:

The HV range is simply a forecast figure based on recent driving habits and fuel usage. How can it calculate what you haven’t yet driven? To rely on it as gospel is foolish. The only figures that matter is the actual amount of fuel used over a given distance. 

I don't think you get it. I own this car for almost 2 years now and the problem is definietly present. The car keep dropping forecasted mileage, even if you don't use the engine.

If you start with 500 forecasted miles with full Battery and drive in the EV mode only, then charge the Battery back to 100%, you would expect this forecasted miles to recover to around 500 but this is not the case. They recover to 460 instead and drop further with every charge. Then at some stage you start the engine and drive in HV mode and the car tells you that you have only 90 HV miles left but you have 30 litres of petrol in the fuel tank. This is an extreme example but similar to a real life scenario.

That's how OP ended up with the fuel reserve message while still having 15 litres of petrol in the tank.

[Flatcoat]

I do get it. As stated by Frosty, the reserve is deliberately large. If you think you have a fault then I assume you have reported it to your dealer? 

[Roger_N]

This is what happened when a HEV was run out of fuel, it is in the US but it maybe of interest.

https://www.youtube.com/watch?v=0s40xNqudDg