Pre-heating the Prius Transaxle and Engine for better fuel economy

[orange4boy]

Photos when I'm next under there. Can you handle the suspense? It's mounted below the inverter coolant pump and the return hose splices into the radiator-bound transaxle coolant hose. The mounting bracket is pushed through the "towing hole". It's a tight fit but not too bad.

The cold line comes from the modded coolant drain plug and passes under the oil pan. I might re-route this one later and make it a hard line. I should have marked the drain plug when tightened before soldering the 90˚ on the end. I had to improvise a gasket there so it would point in the right direction. A union would be better there.

45 seconds for cat ignition? I will have to make sure I wait for that before driving up the hill. Cat preheat? My garage is going to look like the Apollo launch pad soon.

Is there a temp sensor in the cat or do they use the oxy sensor to check for cat temp?

The "plug-in lite" would be great for me because it would warm the battery and give me enough juice to possibly drive up my driveway on EV without loading the engine while the warmup is underway. Who makes a cheap charger? Ha ha.

I'm hoping to be able to be in stage 4 before that though.

The slope coming home does give me a bit of a boost but I'm usually under 60% on return.

[orange4boy]

Edit: These tests include the engine coolant preheat and the transaxle preheat. I will do some runs to separate out the gains from the transaxle preheat later.

This morning, I ran with no preheat. Everything at ambient: 7˚C

1 run@ 6.0 L/100 ambient 7˚ OAT
2 runs@ 5.1 with preheat 7˚ OAT
15% better with both engine and transaxle coolant preheat on a tiny sample size. Not conclusive but encouraging.

(Previous average was 6.3 cold, but that was before getting new tires so I'm starting new figures.)

[bwilson4web]

Originally Posted by orange4boy

Photos when I'm next under there. Can you handle the suspense? It's mounted below the inverter coolant pump and the return hose splices into the radiator-bound transaxle coolant hose. The mounting bracket is pushed through the "towing hole". It's a tight fit but not too bad.

The cold line comes from the modded coolant drain plug and passes under the oil pan. I might re-route this one later and make it a hard line. I should have marked the drain plug when tightened before soldering the 90˚ on the end. I had to improvise a gasket there so it would point in the right direction. A union would be better there.

Excellent! I'm patient ... I've had our NHW11 since Oct. 5, 2005. I can wait a little longer. <GRINS>

Originally Posted by orange4boy

45 seconds for cat ignition? I will have to make sure I wait for that before driving up the hill. Cat preheat? My garage is going to look like the Apollo launch pad soon.

Is there a temp sensor in the cat or do they use the oxy sensor to check for cat temp?

I'm pretty sure it is O{2} sensor #1. There is only a couple of seconds before O{2}#2 lights off. Actually, getting up the hill as much as you can at rpms ~= 1,300 is probably the best strategy. The traction battery energy is left over from the previous trip ... but I could be wrong.

Originally Posted by orange4boy

. . . The "plug-in lite" would be great for me because it would warm the battery and give me enough juice to possibly drive up my driveway on EV without loading the engine while the warmup is underway. Who makes a cheap charger? Ha ha.

I'm hoping to be able to be in stage 4 before that though.

The slope coming home does give me a bit of a boost but I'm usually under 60% on return.

Ok, that works. <grins>

When I first got my NHW11 Prius in October, there was a couple of months of absolute bliss as I was able to find so many resources. I'm just glad to pass one what I learned from those who came before us. <GRINS> ... Ok, maybe I added a few tricks too. <shade>

Bob Wilson

[Christ]

Originally Posted by bwilson4web

Excellent! I'm patient ... I've had our NHW11 since Oct. 5, 2005. I can wait a little longer. <GRINS>


I'm pretty sure it is O{2} sensor #1. There is only a couple of seconds before O{2}#2 lights off. Actually, getting up the hill as much as you can at rpms ~= 1,300 is probably the best strategy. The traction battery energy is left over from the previous trip ... but I could be wrong.


Ok, that works. <grins>

When I first got my NHW11 Prius in October, there was a couple of months of absolute bliss as I was able to find so many resources. I'm just glad to pass one what I learned from those who came before us. <GRINS> ... Ok, maybe I added a few tricks too. <shade>

Bob Wilson

Bob,

Did you rebuild your pack with NHW20 cells? Would that difference adversely affect your results compared to someone else's who still had the NHW11 pack?

[bwilson4web]

Originally Posted by Christ

. . .
Did you rebuild your pack with NHW20 cells? Would that difference adversely affect your results compared to someone else's who still had the NHW11 pack?

I'm still on the original pack and there is no evidence of deterioration since I began monitoring it. I suspect what I've learned about battery maintenance has led to me be being more gentle than ordinary drivers ... it may last a very, very long time.

The only operational mods from a stock Prius:

• Type WS transaxle oil - the same as the NHW20, it reduces drag
• Sumitomo T4s - running 50 psi, they are rated low rolling resistance
• Water noodle lower grill block - in the Fall, Winter, Spring.
• Commuting car only - we have a ZVW30 for cross country and errands

I also have a 1 KW inverter for emergency power but that has no impact on operation.

Bob Wilson

[orange4boy]

I did a run without preheat, but this time I waited for 45ish seconds before driving up the steep part where the engine kicks in. Up to that point it's using the mg2 and the engine idles.

I had a surprisingly good result on that trip although the residual heat in the engine and tranny may have played a part. 12˚ vs 5˚ I will try that again tomorrow with the preheat and see how I fare.

I need a 45 second countdown timer.

Im also wondering if the Prius does not light off the cat after a long ev or warp stealth. I notice that the MPG takes a mighty jump after restart before settling down some seconds later. If so it would be a better strategy to restart but wait till the enrichment ends before putting on the power. If so, it would be nice to have a red/green light for this.

[orange4boy]

Bob,

Apart from parking lots and warm up, Should I be avoiding EV on my trips and P&G instead?

It's so hard to resist the ev mode but am I cycling the battery too much?

[bwilson4web]

Originally Posted by orange4boy

. . .
Apart from parking lots and warm up, Should I be avoiding EV on my trips . . .

Heat is the enemy of batteries and the primary sources:

• Parking in sun in the South - the battery works most efficiently at 'nice' temperatures.
• Avoid high charge events - descending hills or mountains, say 500 ft or more, be sure to use "B" to minimize overcharging the battery.

Charging NiMH batteries is exothermic and generates some H{2} and a little O{2} leakage. This increases the internal module pressure and strains the terminal "O" rings. All of the failed and weak modules I've tested are low on water and I'm sure it is from gas leakage exasperated by high temperature.

Originally Posted by orange4boy

. . . and P&G instead?

Uh, once I'm in Stage-4, I only drive using cruise control ... all the time. I do use "N" when the ICE is warming up before Stage-4 and when stopped to minimize fuel burn. But in all other cases, I used cruise control and seek:

• speeds 38 mph or under
• speeds 45 up to 65 mph
• avoid all others

Originally Posted by orange4boy

. . . It's so hard to resist the ev mode but am I cycling the battery too much?

Go by battery temperature. If you are keeping it moderate, say +5 of ambient, no problem. If you are heating the traction battery much higher, see if you can reduce the heat-up. Otherwise, I see no problem with EV.

My approach on EV is:

1. use the 45 seconds to maximum effect
2. all but last 1-2 miles, ordinary driving avoiding the bad speed ranges (39-44 mph and above 65 mph)
3. maximum range speed, ~18 mph
4. 38 mph works very nicely with a mix of ICE and EV power
5. 65 mph is an excellent highway cruise speed
6. 55 mph is an efficient hill or mountain climb speed (follow trucks!!)
7. ~22 MPG at 100 mph but I don't recommend it more than once per year
8. maximize EV on the last 1-2 miles, speeds of 30-25 mph work great

Bob Wilson

[orange4boy]

Ok,

Good. I don't have to worry about battery temps where I am.

I should still pop off the cover next time I feel like undoing 76+1/2 bolts to check for the dreaded corrosion just to be sure. I bet it causes spot temperature spikes at the corroded terminals which heats up those modules.

I also had a question about the cat in post #36 any insight?

[bwilson4web]

All of my cat studies have been from a cold start. I set the Graham scanner to monitor O{2} voltages and noticed that once O{2}1 starts changing, the ICE 1,300 rpm seems to go a little free-wheeling. I've not really looked at what happens if the car is warmed up and restarted because it seems fairly brief.

Once I get the car in Stage-4, I pretty much try to preserve it. I don't leave it running as I go into a store but if I come back to the house for something, I just leave it in "P" and duck in and out.

One of the perverse things is I think it is more fuel efficient to use a drive-through instead of parking and going inside. This is completely counter to what I'd do with a non-hybrid.

Bob Wilson