Warm up or not?

george3 · Oct 19, 2010

dalsmthme said: ↑

I will throw a few facts and corrections on the table just to help everyone keep calm and carry on. First of all, modern engines DO still drain down. In fact, they are getting worse. I work in the timing drive industry and we spend a lot of time studying how long it takes for oil to get to the hydraulic tensioners and other components within the system. Oil drain down depends a lot on how the engine oil galley is designed. The old way of doing things was to feed the engine from the bottom up. Oil would flow from the pump in the pan directly to a low mounted filter then directly to the main bearings up through the block and into the heads. This design takes a VERY long time to drain because most gerotor pumps will not drain back. The trend now is to put oil filters up high on engines (like Toyota has done for years). This means oil comes from the pump high on top of the engine to the filter then it feeds down to usually a rifle in the block which then branches both up to the heads and down to the mains. With no filter or pump to prevent drain back, these engine completely drain down in 5 minutes or less with an exception of a thin oil film remaining. Every time the engine is fired, it basically has to refill itself all over again. We have measured times as high as 30 seconds on cold starts. Keep in mind, the last thing to get oil in these schemes in the main bearings. Now to Chris’s point about the oil pressure light. Most sending units are located close to the pumps which mean they register acceptable pressure before the engine has actually fully pressurized.

Now as far as oil viscosity. The comment regarding even modern oils being like molasses isn’t actually that far off. Oil viscosity is usually rated at two reference temps, 40C (104F) and 100C (212F). Viscosity curves over a temp range are highly non-linear. They are usually looked at on a log scale. With this in mind, even a 5w-30 viscosity gets very high very quickly as temperature drops. At 0C (32F) 5w-30 has a kinematic viscosity is 541cSt. At -20C (-4F) kinematic viscosity is 2839cSt. The kinematic viscosity of molasses at 100F is anywhere between 281-5070cSt depending on it purity. So essentially, 5w-30 at most winter starting temps (at least in the north east) is equivalent to molasses on a hot day. Viscosity doesn’t change because an oil is conventional or synthetic old or modern. Viscosity is constant across all commonly rated oils.

It’s not just about oil either. It has to do with combustion quality. Fast idle is there to keep your engine running in place of a choke, not to warm the engine. Getting in and going full throttle when cold leaves a lot of unburned fuel to create deposits.

With this said, based on the data I have and what I have seen on dyno tests, I would recommend waiting at least 30 seconds to a minute before you throw any car in gear and drive off. Further, I would recommend keeping the rpms low until the engine has had time to warm (at least until the needle starts to move on the temp guage). This is also recommended by car manufacturers. You can drive with a cold engine, just don’t drive it hard. It recommends this in the Tacoma manual. BMW actually has a meter on the tach on some of the higher models that indicates safe operating rpm until the car is warm. This is a reasonable practice that will avoid any potential issues far down the road.
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Of the 169 posts so far this is the most insightful. Thanks for your time, expertise and effort. Curious George

Tacoyota · Oct 20, 2010

dalsmthme said: ↑

Actually it does drain to the pan, synthetic or not. All oils coat metal surfaces. Plain bearings usually retain just enough oil to start. Lower viscosity oils are easier to pump when cold but are still very thick at cold temps. I would not say they are quick to pump. The big advantage there though is how fast the oil viscosity drops as temp increases. Just trying to properly educate. In the long run, like I said, you can get away with driving it as long as you take it very easy until everything is warm. I just prefer to warm up a touch based on my experience with cold starts on dyno and working with OEM’s.
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Actually u agreed with me . Like i said, a film. Also wasnt saying 5 qts floats and doesnt drain to the pan , of course it does. Compared to older oil standards in the 70/80s modern oils leave the coating/ film / layer that helps minimize friction on startup , synthetics are reported to be especially good at this.

PB65stang · Oct 20, 2010

I think the fact that so many people are so split on this, with both sides having stories of success (mine - '95 Avalon with 250k+ that I never had any problem with, no idle at start) speaks volumes to the fact that letting a modern, fuel injected engine idle when starting up really doesn't get you any extra benefit. But if it makes you feel better, go for it.

I do let my Mustang or other carbureted (or otherwise low-tech) engine warm up for a few seconds, but not for any extended period.

Glamis · Oct 20, 2010

I'm old school I let my truck get to the cold line or just past it. Just not in the morning any time my truck has Cold off completely. I give the Rings, pistons, and block, time to expand. I know new cars run just fine cold and new oils never completely run out the top of the motor. I feel it is Cheap insurance.
I have done this with all my car and trucks.

Sapper26 · Oct 23, 2010

No real reason to in Hawaii.

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