What's your minimum coolant temp for EOC?
 

Oil is much more viscous when it's cold, so I'm hesitant to wantonly cycle the engine on and off before it warms up. Using coolant temperature as a proxy for oil temperature, at what temperature do you decide it's okay to start using the kill switch?

It's been reported on InsightCentral that a Honda Insight with factory programming will enter auto stop at just over 100°F coolant temperature in a warm enough climate, so that's a temp above which it's guaranteed to be safe from a lubrication standpoint. I've been using about 90°F as the point at which I EOC.

But waiting that long costs me plenty of mpg. I didn't reach 90°F until I had exited my neighborhood (four complete stops, 0.3mi). I can do the first 0.3mi on a third as much gas if I EOC from the get-go, which would result in a 6% improvement in my 9mi commute average mpg.

I like to get it higher sooner, mostly from a comfort/safety standpoint, as I like clear windows and warm air. I have been letting it idle in 5th till out of the neighorhood (1 mile) rather than pulse and glide. My mileage out of the neighorhood is down just a bit over pulse and glide, but I get into warmer temps sooner once I get on the higher speed roads.

I don't P&G all too consistently, but I usually don't until the engine is at least running warm. I don't have a number (stock temp gauge is horribly inaccurate), but my engine runs a LOT better when warm. I imagine it has to do with fuel vaporization, but tolerances closing up probably have a small effect.I doubt it takes more than a minute for my HAI to warm up, because it is coming from a heat shield on the exhaust.

I know that didn't answer your question, but usually I wait till I "know" it is warm enough to run better. Probably that means closed loop, but I don't have a way to monitor that.

I don't really have a low limit. I drive out of my driveway (about 300 ft), accelerate and EOC in the 25 mph zone by my house. I use synthetic oil as thin as I can. Right now I'm using 0W-30 and my car calls for 5W-30. I don't have an oil analysis to back this up though.

If your concern is damage to the engine from poor lubrication, then I wouldn't worry about it.

regards
Mech

I eoc more when it is cold as that is where the most benefit is. My warm up takes longer but I use synthetic oil and should be fine.

I start immediately. I have an uphill climb from my driveway to the street, ~200 yd, but from there I EOC for 1/4 mile.

I wouldn't even consider it until full operating temp (180+) has been reached for about 2 minutes, to allow the oil to get warm. If you keep the oil, etc. cold for that long, it's a lot of extra wear on the cylinder walls, more fuel dilution in the oil, as well as more condensation in the oil, both of which require more frequent oil changes.

FWIW, the cylinder wall wear isn't due to cold oil. It's due to cold pistons, cold cylinders and rich running during warmup. The cylinders and pistons aren't quite in their proper shape, etc. yet, which is why cold engines have far more blowby. Things come into tolerance as they warm up. The extra fuel also washes some of the oil off the cylinder walls.

That is pretty much my concern. I have a little valvetrain noise when it's really cold out, and I guess I feel bad about shutting down the engine while it's still clattering first thing in the morning.

But maybe it's six of one, half a dozen of the other. My engine can warm up in neutral while I roll to a stop sign, or it can warm up while doing something useful a little while down the road.

Oil will have worked its way through the engine by the time I'm going 5mph in the driveway and ready to hit the kill switch.You got it. The shorter your warm-up is, the faster you're spending energy on things other than propulsion. It takes me about four miles before I can turn the heater to "H", and another mile before the temperature recovers so that I can turn the fan on. Defogging windows just doesn't happen. But if you park in the garage with a window open, fogging doesn't happen.

On my 1937 Ford it had a starter button separate from the ignition switch. Even after sitting for a week or more, you could just run the starter for 5 seconds with no ignition and see 60 pounds of oil pressure with a cranking speed of 100 RPM or less (original 6 volt direct drive starter-about 1/3 the cranking speed of a modern engine).

Modern engines with oil filters with check valves produce oil pressure within a second of cranking, and if you are not seeing the light come on you still have some pressure.

Modern oils, in particular those that are designed for the start stop sequences of hybrids will not cause you problems with EOC cold, anymore than they would hot. Most of the noise you hear cold is the pistons in the Insight and it was the same on my VX. Once the pistons heat up and expand the noise goes away.

My grandfather once drove his 39 Ford police car 40 miles after an oil change when they forgot to put any oil in the engine. It finally locked up.

You are not restarting the engine and racing it or driving aggressively, so I doubt you will ever see any problem. I always start and go. No reason to use fuel because you have plenty of oil pressure cold, in fact it is probably twice the oil pressure as warm on may engines.

I think it is a non issue, and in 750,000 miles and 44 years I have never seen any situation where I could blame any damage on what you wish to do.

It will prolong your warm up time, but if you are getting better mileage overall, and can handle the wait for heat then go for it.

regards
Mech