Engine Braking, Cold Engine = ?

[GarrettSocling]

I have a question:

My inlaws live on the side of a hill, about 2 miles of pretty straight incline on the way up. I let my car run for 30 seconds or so after getting to their house to let it cool off before turning it off.

Then, on the way home, I head down the hill with a cold engine. I usually put it in third and engine brake to about 3000 RPM, which is 45MPH in my Corolla.

Is this harmful? Bad cold, harmless warm? Harmless cold, harmless warm?

TIA,
G

 

[KW]

I would not do it unless you normaly spin the motor up to 3000 RPM cold.

 

[JHZR2]

Ive read that even on very well designed, non-oil consuming engines, that when doing engine braking in MT cars, minute amounts of oil slips through into the chamber and then goes out the exhaust system. Typically it is minimal, and proably amounts to less than a thimbleful in most situations, over an entire OCI.

However, if your cat isnt hot, any sulfur content in the oil will tend to run a higher chance of damaging the converter - not to mention the other additives in the oil. Not as much of an issue since API SM, but still something to think about.

I always figure that brakes are a lot cheaper than engines. Why not use the brakes a bit more and coast part-way? Note: this may not be safe, I dont know the hill you drive on.

Sometimes youre dealt the hand that you havem and there isnt much that can be done - you may just have to drive it. Extended idling wont do anything great for your car, so I wouldnt think about warming it up further in place.

JMH

 

[GarrettSocling]

Thanks for the ideas. I wasn't sure if there were any negative side-effects of engine braking, but if there is a chance, then yes: brakes are a lot cheaper!

I usually shift at 3000 RPM when cold, so the car is only 3000RPM momentarily.

Since the car is engine braking, it isn't generating much heat and the coolant needle usually doesn't move a bit from the top of the hill to the bottom: I don't touch the accelerator once, typically.

I am running M1 5w30, and have been checking it regularly for consumption. I'm at about 4000 miles and it doesn't look like the level on the dipstick has moved a single bit. The clarity is still good, starting to get a slighty dark tinge. I don't think it is consuming much oil, but I only do this drive once a week.

I've been thinking about this for as long as we've been together, one of those things which I think of for about 15 seconds once a week, and then not at all the rest of the time

Thanks,
G

 

[JHZR2]

once a week is no biggie.

Just make all your shifts at 3000 rpm or lower, as a rule, and your engine will last and last, and youll get super high fuel economy as well!

JMH

 

[Palut]

3k rpm at 45 mph? That sounds EXACTLY like my 3rd gear! With a cold car, I'd coast down that hill in 4th, using the brakes to stay at my desired speed. Even if you're not putting much load on the engine, the parts still don't fit each other quite right when they're cold, and the oil is still thick, so you still want to avoid high rpms.

FWIW, I like to stay under 2800 rpm until the coolant is at normal temperature.

 

[eljefino]

OTOH, there is an ideal temperature for brakes which is sometimes a bit warmer than ambient. If you rode your brakes down the hill you could consider yourself to be properly getting the car ready for highway traffic.

 

[JohnBrowning]

How else are you supposed to control your speed on the decent? Engine brakeing is ok. Generaly you you either use the same gear you used to climb the hill or not more then one gear lower. It depends on how the transmission is set up.

Once you have the right gear for the decent you allow the vechile to exceed the decent speed not more then 5 MPH above your decent speed then you brake to 5 MPH under you required decent speed and start all over again!

I am preety sure that your carolla does 3000 RPMS going 70-80 MPH ont he freeway with a 5000-6100 rev limiter. You will be fine. You would be silly to try to control your speed soley with your breaks!