Piston Slap: Improper Engine Warm Up Procedure?

Sajeev Mehta
by Sajeev Mehta
piston slap improper engine warm up procedure

TTAC Commentator Arthur Dailey writes:


Thanks very much for posting my question. Your answer and the comments from others were most informative. How about another?

We now have only 2 licensed drivers in our home. We do however have 3 licensed cars in the driveway. Please do not ask about the project car in the garage. 2 of the cars are our ‘daily’ drives, the 3rd is used primarily on weekends. We live less than 3 minutes from a 400 series highway in Ontario. That means that the cars can be required to reach highway speed before they are ‘warmed up’.

My normal practice last winter was to get up, start all the cars, turn off all possible drains on the batteries. Then take the dog to the park across the street, stretch our legs and let him do his business. After about 10 minutes we return. I then turn on the heater/defrost on the 2 cars that we will be driving and scrape/brush them. When this is completed, I turn all 3 cars off and go back into the house to get myself ready for work. You may all remember what last winter was like and the upcoming winter is supposed to be similar.

Now I understand that idling is environmentally irresponsible. And possibly against by-laws in some areas. That however is a discussion for another forum.

My questions are:

  1. Is this OK for the cars?
  2. Am I better off warming up/idling our weekend car like this or leaving it all week and hoping that it is OK to start on the weekend.

Please do not suggest:

  1. A trickle charger
  2. Engine block heaters

I would love to have those as options, however none of the cars have block heaters installed and there are no electrical outlets available for either of the above suggestions (thanks to the project car).


Arthur Dailey

Sajeev answers:

Okay! I will not mention your Project Car, nor your need for conventional starting aids in cold conditions. Even if your engine warm up procedure absolutely demands otherwise!

In general, start-up a cold motor and drive it ASAP in a modest, moderate manner. What does that mean?

Perhaps that means not accelerating past the motor’s torque peak, unless necessary for merging onto a freeway. If you own a torque-less, rev-intensive motor à la Scion FR-S, the torque peak notion is invalid. No matter, avoid heavy throttle application until oil temperature is up to normal: think about your unique engine type/driving condition and apply common sense.

Thanks to advancements in fluid technology and the widespread use of synthetic-blended oil, it’s gotta be disturbingly cold ( handy chart here) to do otherwise. On to your questions:

1. Why are you turning off the cars after warming them up? No! Do your stuff while they idle/thaw (when needed) and then drive! You are only hurting them more by letting the fluids cool down again. Change your morning routine ASAP.

2. There is no reason to start-up your weekend car just to charge the battery. If the weekend car is impossible to start after 5 days, get a battery blanket (Oops! No power right?) and disconnect the negative cable to minimize drain. Or just give up and yank the battery, leaving it somewhere isolated from the ground, like a wood table. More work, but if you can physically handle that heavy of a load, the exercise won’t kill ya.

No matter what, you gotta change your warm up procedure.

Bonus! A Piston Slap Nugget of Wisdom:

Remember that oil temp isn’t measured on the (coolant) temperature needle on your dashboard. Oil takes longer to warm up, so if you aren’t fortunate enough to have a sub-menu showing oil temp, or you don’t have an app for that, wait a little while after the temp needle is happy. That makes the oil happy too.

[Image: Shutterstock user Pixelcruiser]

Send your queries to sajeev@thetruthaboutcars.com. Spare no details and ask for a speedy resolution if you’re in a hurry…but be realistic, and use your make/model specific forums instead of TTAC for more timely advice.

Join the conversation
2 of 114 comments
  • Speedlaw Speedlaw on Jan 11, 2015

    Never had this problem. Slow suburban driving for five minutes or so, then gentle on ramp....by the time drama is required, the car is warmed up. One thing to point out to the Brown Manual Diesel Masses here. The increased efficiency of the diesel is a problem on the school run cold winter mornings. If I take the gas rigs, the heater is going half way to school, and the car is warm upon return home. If I take the diesel, the only warmth you'll see on the trip is the seat heaters and the "have a nice day" goodbye hug. The TDI heater is great down to -20, that I've seen, it just isn't fast...

  • AJ AJ on Jan 25, 2015

    My daily driver only sees the inside of my garage from December through March. During that time my toy (a Jeep) gets put into storage. I started doing this three winters ago and its been the best decision ever.

  • Wolfwagen I would rather have an annual inspection that may catch something early or at least the driver can be informed of an impending issue. Government vs private is another issue and unscrupulous mechanics is another.On a slightly different topic is the inspection of salvage or rebuilt cars. In NYS it is strictly to ensure that stolen parts were not used to rebuild the vehicle. I would rather see an inspection to ensure that the vehicle has been properly put back together.
  • PeterPuck For years, Ford has simply reworked existing designs originating from Europe and Japanese manufacturers, not being capable of designing a decent car in the USA.What’s the last clean sheet design from the USA? The 1986 Taurus?And they still can’t manage to get things right.why is this? Are they putting all of the competent engineers and designers on the F150? Is woke diversification affecting them, as some rumours suggest? Are they rewarding incompetence?
  • Brandon What is a "city crossover"?
  • Tassos What was the last time we had any good news from Ford? (or GM for that matter?)The last one was probably when Alan Mulally was CEO. Were you even born back then?Fields was a total disaster, then they go hire this clown from Toyota's PR department, the current Ford CEO, Fart-ley or something.He claims to be an auto enthusiast too (unlike Mary Barra who is even worse, but of course always forgiven, as she is the proud owner of a set of female genitals.
  • Tassos I know some would want to own a collectible Mustang. (sure as hell not me. This crappy 'secretary's car' (that was exactly its intended buying demo) was as sophisticated (transl. : CRUDE) as the FLintstone's mobile. Solid Real Axle? Are you effing kidding me?There is a huge number of these around, so they are neither expensive nor valuable.WHen it came out, it was $2,000 or so new. A colleague bought a recent one with the stupid Ecoboost which also promised good fuel economy. He drives a hard bargain and spends time shopping and I remember he paid $37k ( the fool only bought domestic crap, but luckily he is good with his hands and can fix lots of stuff on them).He told me that the alleged fuel economy is obtained only if you drive it like a VERY old lady. WHich defeats the purpose, of course, you might as well buy a used Toyota Yaris (not even a Corolla).