CAT Wizards,

Mnay people have asked me the following question: Why do you have to pre-heat fwith the glow plugs for so long (I typically do the pre-heat for 1-2 minutes). They tell me that their newer diesel engine (in a New Holland ag tractor which is ~35 HP) only preheats for ~10 seconds or less. Then the next statement is: There must be something wrong with your CAT dozer.

I know there is a techical difference associated with precombustion engines and direct start diesels that still use glow plugs and this is a component of the answer. However, I don't know the techical details and would like to know. I amsure there is a post out there that describes this but have not had lots of success finding one with the full answer.

Help and Thanks!!

The Cat engines with the pre combustion chambers normally with direct start has glow plugs to warm it up in the chamber but when Cat went to the direct injection then it wasn,t needed.It,s all in the engineering why the glow plugs are needed for one & not the other.To save batteries it,s always good practice to keep a can of starting fluid handy in case it,s needed when it,s real cold out to help give the engine a quicker start.

Bill, the precup engine has a much lower nozzel pressure and lower compression ratio. You get less heat from compression and a less fine spray of fuel than a direct injection engine. The glow plugs make up for the less heat. The starting engines pipe their exh out through the intake to heat the intake air. A precup engine needs a bit of cranking without fuel on start up to build more heat aswell.
Later Bob

AJ if you were here years ago when the winters got very cold with the older style prechamber engines you would need the starting fluid to get going in the morning. In the coal strippings they all kept a can on their tractor if needed & I as an engine mechanic for the Cat dealer for 36 years I never saw one engine damaged from starting fluid esp. if it was used right.Cat even installed had units to dispense it as an option if so needed.

Wizards
Thanks for the feedback. The lower compression and nozzle pressure necessitates the use of the glow plugs for a longer period combined with cranking with no fuel to build up heat (just like the pony motors it seems). This apparently creates the heat conditions that rival what's needed by the direct injection engines if I follow the explanations. I have no operators manual and did not know the time required for heating.with the glow plugs. From what I recall the amp guage is in the 20 amp range while heating. I have found that heating for 45 seconds in warm temps (above 60 deg) works well and in the 1 min 30-45 seconds works in cold temps (<20 deg)with no ether used. A sniff of ether will reduce the heating time then if I follow that correctly. It does not help that the tractor sits for a month or 2 between starts. I am guessing the battery power is lessened and I get less spin speed and combustion heat build up when I do crank. Thanks again

Bill most of those tractors had a plate on the dash telling you the preheat time at different temps. Glowplugs draw 5 Amps per plug go 20 amps is good.
Later Bob

Rats. I typed a reply on a blackberry and apparently it went to never never land. I will try again in the morning

I am going to buy an operators manual and do what's recommended. I am now more informed than I was before. Thanks guys

Use ether with caution (if at all) when also using glow plugs or other air heating devices. Most times it's either one or the other, but not both.

The point at which the engine will run ultimately depends on the combustion temperature of the fuel and the incoming air temperature. Injection of fuel and compression of air create the conditions that support combustion.

Each small droplet of diesel from the injector will have a point at some distance from it's surface where the air/fuel mix is right for ignition at some minimum temperature. too cool, no ignition, hot enough, it will burn, hotter than that, it will burn fast/completely enough to accelerate the engine until the governor takes over. Finer fuel droplets make more possible points of ignition, and faster burn when they do ignite.

Compression of the air charge makes high pressure/temperature, higher compression/faster cranking makes higher pressure/temperature etc. Glow plugs etc raise the incoming air temperature so the final temperature after compression will be higher/high enough for ignition.

Ether lowers the temperature of ignition.

Hi team,
todays modern precomb. engines are fitted with glowplug timer/controlers to govern the glow time and power to the glowplugs after glow has been reached. These are usually low voltage units (3-6 volt) and would fail if over glowed, this is done to shorten glow times for the impatient driver !
Cat uses higher voltage glow plugs for engine safety at the expense of long glow times --a simpler more robust and fool proof system for it's day. Failed glowplug tips make a good mess of an engine cylinder and valves ! so do not over glow.
The controler/timer cooling system temperature sensor on my old MQ Nissan Patrol partially failed and did not glow for long enough. I fooled it by putting some extra resisters into the circuit to compensate, worked well.
I have here a Serv./Mag. article Nov. 30 1950 which is 3 pages long!, on the Ether Starting System, any interest?
Cheers Eddie B.