Strange behavior and cold weather

Good morning, everyone.

I'm fortunate enough to have an insulated garage that stays substantially warmer in the winter than it does outside. The majority of this winter my car has started in the morning at 30 to 40°F rather than the significantly colder temperatures we've had outside.

Yesterday it got its first run in a week-and-a-half after sitting outside, it was 5° out. It started and drove just fine, but I noticed some interesting engine behavior when I got on the highway. Beyond a certain throttle point the engine would rapidly change rpm from midrange to near redline and back again. Power output seemed to remain constant, and I never had any check engine lights, so I'm wondering if this is part of the cold-weather warming strategy? Has anybody else experienced anything similar?

It acted like this a few weeks ago after being parked overnight and starting at -15°, but normal operation resumed when the engine got up to temperature. This thing takes a LONG time to warm up when he gets this cold.

 

Thanks, guys.

The 12 V battery was new three months ago, and has given me no indications of an issue. After sitting for 10 days it had no issues starting the system, and likewise my hybrid battery was showing nearly full bars after that time. I check coolant and oil regularly, all of which have been changed in the last few months and are showing right within range. It's probably nothing to worry about, I just figured I would ask.

Have you noticed as much of a difference with this? I've always been skeptical, in theory with a closed thermostat there should not be any coolant flowing to the radiator, so I've never attempted to block anything off.

I haven't noticed any skew in MPG, but I have a harder time getting a full reading on the fuel tank, and it seems to be holding less fuel. I figure it's normal for the temperature and age of the car, but definitely a strange quirk with the previous compared to other cars.

 

This always makes a thread really long, because everybody has their own opinion. Lol much like an oil thread.

I start mine and drive immediately, making sure to be easy on the throttle until the engine comes up to temperature. Just like every other car. Everything I’ve read suggests that running below operating temperature is not good for an engine, and idling is the most inefficient way for an engine to warm up. So I try to get mine up the temp as fast as possible, even when it’s cold out.

 

I've not read that, but not saying it's false either. If you can find a source I'm all ears, I'm always up for challenging my assumptions.

I did a lot of reading about this over the years, as is always a topic that comes up on Internet forums and such. I'm kind of obsessive about efficiency is well, so I start off being biased against letting an engine run for no reason. I get comp at any data or reputable source that suggests that is necessary. The only exception were the two diesel pickups I had in the past, both had a note in the owners manual about the PCM forcing idle-only for as much is 20 seconds during "extremely cold weather". I don't believe I ever saw this message come up, and my understanding was that it had more to do with the fuel system than anything else.

 

Haha...now that turned quick. You were asking about how long people let their cars idle, and now it's "You're the one having the problem, not me". Nice.

My engine is working just fine, thanks.

 

I'm a bit south of you in Minnesota, but we've had a relatively cold winter for the most part. In contrast, most of my driving is highway miles, and I roll over 2000 per month with my typical schedule. My car was not built with a block heater, and I never have one installed, but it has the advantage of starting from an insulated garage that's always a good 30° warmer than outside temps.

In the worst of the "polar vortex", overnight temps went down to -30°F and my garage was around 10°. But even during those subzero temperatures my fuel economy never dipped below 35 miles per gallon. My worst tank was the most recent one I filled had the most idling to clear the windshield off. The fact that I can get above 35 mpg with no idling at all suggests to me that cold transaxle and sub-optimal engine temperatures are less harmful to fuel economy than extended idling.

I haven't driven it much in the last two weeks because my van is in the shop for a warranty repair, and their150 mile-per-day allowance means I put most of my miles on the brand-new Jeep Cherokee they put me in. I hope to get my van back in the next couple of days, and my Prius will stop feeling so neglected.