Overheat protection -- firing every other cycle

[Raven]

This forum has been so far, pretty helpful with the last couple of questions I had and I want to say keep up the good work!

Anyways back when I was in college with automotive classes I heard a comment from one of my instructors at the time. He said that some older cars (might have been Cadillac) had a special overheating protection "mode" where if it detected an overheating situation, it would switch to firing the cylinders every *other* cycle, as in firing every 1440 (four rotations) of the crank on all the cylinders. Apparently that was to help cool the engine down a bit, obviously it wouldn't run so hot, neither would power be worth writing home about but apparently at least you could limp home.

Does this sound familiar to anyone? It sounds like a good idea, if it worked, that is. Considering that I haven't heard any mention of it any other time, and the two times I nearly overheated an engine (on 4.6L V8 out of a '98 Ford van, and the other being one of my older E30s*) they never went into such a mode, so there must be a reason for it not being adopted if it did in fact work pretty well (like sticking people with $2K repair bills).


*: I had a 325e that had the 80A alternator. The bearing went out on it so I got a replacement 90A unit. Later E30s had the 90A but I thought they would work fine. Turns out they didn't because the 90A sits at a slightly different angle, causing the v-belt to flip. Literally. Flip upside down and stay on the engine. It lasted "upside down" for about 20mi/32km and then promptly broke as I got off work one day early. Limped home by running it until it would get close to the red, shut off and coast to a stop -- each stop was about 45 minutes in duration until it would get somewhere back in the middle. Effective driving time was about one minute -- and I was only about 3mi/5km from home so instead of 10 minutes driving & five stop lights it was three hours. Lesson learned.

 

[actionstan]

My 2003 Buick had something similar in the owners manually, I cant recall if it would deactivate some cylinders, or fire every other rotation however..


EDIT: Here is what I found in a buick century owners manual

Overheated Engine Protection
Operating Mode:

This emergency operating mode allows your vehicle to
be driven to a safe place in an emergency situation.
If an overheated engine condition exists, an overheat
protection mode which alternates firing groups of
cylinders helps prevent engine damage. In this mode,
you will notice a significant loss in power and engine
performance. The low coolant light may come on
and the temperature gage will indicate an overheat
condition exists. Driving extended miles (km) and/or
towing a trailer in the overheat protection mode should
be avoided.

 

[SHOPete]

Standard feature of Cadillac Northstar V8 which was also used by Oldsmobile and Buick. Pretty good description here Google http://bit.ly/ISn5jo and other places. Google "northstar limp home mode."

 

[Nick R]

I know our expedition had this too- in fact I think most cars have this, but I could be wrong. I'll look through the focus and traverse OMs later to see if they mention anything about it.

 

[itguy08]

Ford's been using it for a while on a bunch of their engines, especially the Modulars. The way it works is the engine will go up into the Hot area but you can keep going. You will feel it kick in cause you will loose a lot of power. Here's Ford's take from the 1998 F150 Manual:

Quote:
What you should know about fail-safe cooling (if equipped)
If the engine coolant supply is depleted, this feature allows the vehicle to be driven temporarily before incremental component damage is incurred. The “fail safe” distance depends on ambient temperatures, vehicle load and terrain.
How fail-safe cooling works
If the engine overheats, the engine will automatically switch from eight to alternating four cylinder operation. Each disabled cylinder acts as an air pump and cools the engine.
When this occurs, the engine coolant temperature gauge will move into the red area and the
light illuminates.
The service engine soon light will illuminate, indicating that vehicle service is required.
The vehicle will still operate, but will have limited engine power and no air conditioning capability.
Continued operation will increase engine temperature and cause the engine to completely shut down. The vehicle will coast to a stop.

Maintenance and care
As the engine temperature cools, the engine may be re-started. Take your vehicle to a service facility as soon as possible to minimize engine damage.
When fail-safe mode is activated
• Pull off the road as soon as possible.
• Immediately turn the engine off to prevent severe engine damage.
• Wait for the engine to cool.
• Check the coolant level.


I believe the Nissan VQ also has a similar system as similar verbiage was in the manual of my 04 G35.

I know my Taurus also has it and I think all the 3.5 Fords feature it as well.

 

[Rand]

some of the ford duratech's had it also..

the 2007 focus for example.

 

[Roadkingnc]

On the fords it has to get pretty hot to get it to activate, like 255 260 degrees

 

[SteveSRT8]

I have enjoyed this feature since the Vortec series V8's came out in our fleet.

Nuttin' new here, Gm and most of the majors have had this for decades along with the ability to completely cut the spark if oil pressure dips too low, etc.

 

[Raven]

So on a V8 it operates like a 4cyl on each opposing bank.

How well does it actually work though? They say not to go for extended periods, so there must be a reason they're saying that.

I would assume it works the same on a V6, on an I4 or I6 I wouldn't know how they'd implement that. I6s aren't seen often in American cars, aside from certain Jeeps with the 4.0L I6.

I wonder if it'd work with a rotary

 

[Vikas]

How exactly are they able to beat the physics involved though? Don't the cylinders now have to work twice as much to be able to deliver the same amount of power necessary to move the vehicle? I mean the power requirement from the vehicle has not gone down and you have not made the engine more efficient either or have you??

Seems like yet another gimmick similar to perpetual motion machines

 

[cptbarkey]

i'm wondering in practice that the engine still craters anyway. I wouldnt call it insurance or go ahead and experiment, but its interesting anyway.

 

[yonyon]

Originally Posted By: Vikas
How exactly are they able to beat the physics involved though? Don't the cylinders now have to work twice as much to be able to deliver the same amount of power necessary to move the vehicle?
Yes, but the maximum power output is cut way down.
Originally Posted By: Vikas
I mean the power requirement from the vehicle has not gone down and you have not made the engine more efficient either or have you??
If anything it's slightly less efficient because it's pumping twice as much air through the engine. That air provides some additional cooling directly to surfaces that see fire.

 

[CBR.worm]

And it gives you notice that something is wrong. People may not notice that the temp gauge is high, but they will notice if their vehicle can only maintain 35mph and sounds like an 8 stroke.

 

[Vikas]

Originally Posted By: CBR.worm
And it gives you notice that something is wrong. People may not notice that the temp gauge is high, but they will notice if their vehicle can only maintain 35mph and sounds like an 8 stroke.
Surely, there must be easier way to attract driver's attention and to make sure he is still not bombing away!