Just a question - starting an engine for ~30 seconds without coolant in it... will it hurt it? I'm slightly worried about accidentally warping heads, or what not..

I don't think 30 seconds would cause much problem without coolant as long as you don't go above idle.

There's a lot of mass in an engine that can absorb a lot of heat before requiring it to be taken away by coolant.

Don't add cold coolant to a hot engine tho. Make sure you give it a couple hours to cool down before adding any coolant after running it.

Not good for the water pump but 30 sec should not have done any damage

[This message has been edited by CC Rider (edited 01-14-2004).]

I'd take the fanbelt off so the waterpump won't spin... the seal can be damaged really quickly if the pump is spun dry

Okay good.... In that case, I'm gonna go listen to my Northstar via telephone

should be Ok for that short a period. Some drag cars dont even carry any water for a run. Cast iron block and heads will take more abuse than aluminum. If you got alum engine, soon as it says HOT, you better shut off and coast to the side or your engines junk. I blew a heater hose on a Mustang and drove it several miles on freeway to next exit with no problem.

Will not hurt a thing for a few sec, you could actually let it run for a few min without hurting anything aslong as you watch the temp and do not let it overheat.

if your running an N* without coolant it will run quiet long as the temp sender will tell the engine to go into hot limp mode. The loss of coolant "limp home" mode is automatically initiated by the PCM if it senses extraordinarily high coolant temps based on input from the coolant sensor in the cylinder head.

The coolant temp sensor location was developed such that it senses coolant temp circulating thru the head when it is "wet" or covered by coolant. Should the coolant level fall even slightly in the engine the sensor will be uncovered as it is near the highest point in the head coolant jacket. If uncovered, or "dry", the sensor is designed and positioned such that it will sense the rapidly rising temperature of the exhaust port wall, thus responding to high "high metal temps" as well.

Before this happens the low coolant warning should be on and two different coolant temp warnings should be displayed.

When the PCM senses that the temp sensor is so hot that it has to be 'dry" and uncovered it switches in to the "limp home" mode to keep the engine running without damage so that you can drive to a safe place.

The limp home system works by turning the fuel injectors off to four cylinders allowing them to stop running but they still pump air thru the cylinders to cool them down. Those four cylinders will be shut down for a predetermined number of cylinder firing events while the other four provide power. After the predetermined interval those four cylinders start firing as the injectors are reactivated and the other four cylinders are turned off by disabling the injectors so that they can cool. The two groups of cylinders shut down in sequence are 1-7-4-6 and 2-3-5-8. The cylinder group operation is regulated not by a timer but actually by counting the number of firing events each group sees. This was much more effective at protecting the engine than a simple timer. In limp home mode you will notice that the two groups switch much more slowly at idle and then rapidly at higher speeds because of this.

There are other things done with the idle speed, fueling, spark advance, etc. in concert with the cylinder cut out but the main function that makes the limp home system work is the cylinder cut out. Remember, the valves are still operating so the cylinder still pumps air thru it...making it an internally air cooled engine when in limp home mode. This is often confused with the DOD (displacement on demand) system upcoming on GM engines and the older V-8-6-4 system on the 81 Cadillacs. They are not the same as the Northstar limp home mode. In DOD the valves are actually disabled so that they stay closed to disable the cylinder. Just turning off the fuel to disable a cylinder causes huge pumping losses that are immediately evident trying to drive the car. With only 4 cylinders running and 4 dead but still pumping the engine has the net output of about 1.5 cylinders as much of the power goes into the pumping loss of the dead 4 cylinders. In DOD, the gases trapped in the cylinder act as an air spring returning the power used to compress them to he piston on the down stroke.

If the engine needs to implement the limp home mode it can safely go 50 miles at 50 MPH with no damage. This has been tested and documented by several unbiased (actually they were biased...they figured it would not work and tried to prove it...and ended up proving that it DOES work very well)

If limp home mode is ever used the engine oil should be changed immediately after when the cooling problem is being fixed. The oil gets extremely hot when the engine reverts to limp home mode as the oil takes over part of the task of cooling the engine

Wow, thanks for the long and informative post! I wasn't sure if the "limp without coolant" only applied to the 2000+ models or what.. I was more concerned with localized uneven heating warping things... As a side note, I listened to it, and does it purrrr Quiet too... could barely hear it over the phone.

I've been under the impression that you're OK (tho obviously not the best for the engine) to run an engine into extreme temperatures, BUT if the engine stalls out DO NOT TRY TO RESTART IT! that's when the problems start happening (like cracked pistons, warped heads, broken rings).

quote Originally posted by DCsoundNut: I've been under the impression that you're OK (tho obviously not the best for the engine) to run an engine into extreme temperatures, BUT if the engine stalls out DO NOT TRY TO RESTART IT! that's when the problems start happening (like cracked pistons, warped heads, broken rings).

NO NO NO that will kill an engine, also if you add cold water to a hot engine you can drive directly to the nearest engine supplier and buy a new one. 'cause the one you have won't ever be the same.