How long do you let her "warm up"?

[rbargeron]

My 2 cents is it is important to keep the RPM down after cold starts.

When a tractor starts with cold engine and hydraulic oil, viscosity is high, and the internal forces on everything are high. Oil circulation is slow and backpressures on pumps and valves are huge. Cylinder wall oil film is very thin from sitting. The situation improves a lot with only a few minutes running. I try to give it 1-3 minutes at idle but sometimes I cheat and start rolling sooner.

If a machine is allowed to run slow for a little while before it is loaded, it will last longer.

I always run slow for a little while before I get loaded, and I've lasted quite a while.

 

[Glowplug]

Is there something specific to Diesels?

Yes. . .

 

[_RaT_]

Yes. . .

Hmmm, I see, interesting.

 

[rdsaustintx]

<peek>

Oh. This is about tractors.

<unpeek>

 

[Glowplug]

I suppose you wanted some specific explanation.

I don’t know much about engines or the specifics of the mechanics of diesel engines but I have my own explanation as to why warming up a diesel is important. Most everyone knows the combustion chamber is different in diesels than in standard gasoline engines. There is no sparkplug in a diesel. The ignition of the fuel is basically done from the heat of the engine and is a self-perpetuating process. So, as the engine gets warmer the whole fuel burning process gets better and easier for the tractor. Also cars don’t have the same hydraulic set-up like tractors do. Getting the engine oil in the crankcase warm is one thing. But the hydraulic oil is the tractor’s “life blood”. It controls and lubricates many parts at the same time. It’s even more important in a hydrostatic transmission. There the oil is not only the lubricant but an integral part in the function of the transmission itself. Hydrostatic transmissions are not like automobile automatic transmissions. They are basically a fancy hydraulic circuit. They are a closed-loop hydraulically powered motor with variable speed. And everyone knows how important the oil is to hydraulics.

No matter what type of vehicle you’re talking about the oil will settle and cool and not be protecting the parts when the vehicle is sitting at rest. You really don’t want all that cold dry metal rubbing against other cold dry metal at a high speed before it’s had a chance to be coated in warm lubricating oil. Unlike automobile combustion chambers many diesels have very “tight” engines. This means that the space between the cylinder and the engine block is almost non-existent. It’s metal on metal. When first started you have cold metal once again contacting cold dry non-lubricated metal. As the engine warms the parts are not only coated in warm lubricating oil but they expand somewhat, thus creating more space between the metal contact points and thus less metal on metal contact. Oil’s viscosity changes in relation to the temperature. This viscosity-temperature relationship is called the viscosity-index and is a standard measurement. Interestingly, this viscosity index is measured between the temperatures of 104F and 212F, which is considered “operating” temperature for oils. If 104F is considered the minimal “normal” operating temperature for oil then why would you go tearing across the field putting excessive stress and load on the engine parts when the engine oil is obviously very much below that temperature? Much of the reasons for warming up an engine apply to both an automobile and a tractor. But a diesel IS different and thus more important to warm up first. I suppose that’s the reason that many truckers will leave their rig running often for hours as opposed to turning it off and restarting it.

I don’t know much about the topic. Heck, truthfully it may be better to not do a warm up. Perhaps some of the other guys with more mechanical engineering and fluids knowledge know better and can explain. But the information above is all I’ve got in my tiny brain and that’s the reason I warm up my tractor for about 10 minutes before doing any serious work.

 

[rbargeron]

.....The ignition of the fuel is basically done from the heat of the engine............as the engine gets warmer the whole fuel burning process gets better and easier for the tractor............

Couple points - diesels fire due to the heat of compression (PV=RT), which is only partially affected by surrounding engine temperature. The firing is less energetic in a cold engine and becomes more forceful as it warms up. Piston fit in gas and diesel engines is similar - cold fit clearance is greater than warm fit because pistons are aluminum, block is iron. Alumninum expands more with temperature. Cold engines allow more blow by and shove more combustion debris into the ring grooves - that's a reason not to work any engine until it warms up and better running fits are established.

 

[Glowplug]

Piston fit in gas and diesel engines is similar - cold fit clearance is greater than warm fit because pistons are aluminum, block is iron. Alumninum expands more with temperature. Cold engines allow more blow by and shove more combustion debris into the ring grooves - that's a reason not to work any engine until it warms up and better running fits are established.

Cool. Thanks for the explanation. I welcome any comments, corrections, etc. because like I said, my statement above is just my own understanding and I'm no expert on the topic. My bottom line is that the cost 5 or 10 minutes of diesel fuel at above idle is miniscule. But even if it helps the engine only very minimally it is worth it.

My dealer told me when he deliverred it that it was really important to warm up my M7040 due to the "tight" engine. I guess I just assumed that as it warmed the clearance would be greater. But it does make sense what you say due to the different rate of expansion of different metals. If there was a larger gap I guess something could lodge in there and cause damage. So I'll continue to start slow and warm up before throttling up.

 

[rbargeron]

The dealer's advice about a "tight" engine may refer to the likelihood that newly-assembled machines have many little microscopic rough edges and surfaces that have not yet been burnished into being a smooth fit. How much of this there is depends on the precision of manufacture. I think in Kubota's case the component part quality is well-above average to begin with so it's less of an issue. But I remember a tractor dealer who imported some 50-75 hp Zetor tractors. He said when they did the 50-hour service on them it wasn't unusual for 1/2 cup of metal filings to drain out with the break-in oil !

 

[paparammer]

Two things: engine and hydraulics. It's fairly easy just by sound to know when the engine is running smoothly and presumably it warms up before the hydraulics will. After the engine is running smoothly, I test the hydraulics by trying to raise whatever is attached: FEL, snowblower, blade, whatever. If that process is slow or elicits a groan from the tractor, I wait a while, otherwise, off we go. Perhaps a little slower at first but not for long.

 

[DmansPadge]

This subject has always amazed me a bit. I always warm any engine before any real use. It only makes sense to me to do so. The hardest thing on an engine is a cold start.... oil has drained down, clearances are greater, etc. My rule of thumb for my vehicles is to let the temp gauge begin to register. Usually about 3 min. during summer and 5 during winter. My tractor takes forever to register... so the old 3-5 minute rule is roughly what I use for it and other equipment that doesn't have temp. gauges. That being said... I see on a daily basis, cars, trucks (diesel or gas), tractors, mowers, and everything else that has an internal combustion engine cranked up and used immediately. Some of them may have 250,000 miles or 10,000 hours. It is kinda hard to say that the old "start and go" method is hurting them much. There is also tons of equipment such as generators that will run full throttle all the time... warm or not. I'll just keep warming up my equipment.... maybe it doesn't make that much difference... but it sure makes me feel better.