What is your warm up procedure for your M38a1?

[linx310]

Since I have every thing squared away now on my M38a1 I can take it for some decent drives.

The issue i am having are operator induced.

At first I had trouble getting the thing started after it has sat for awhile. I think I have found a start up procedure that works well for me.

1. Full Choke
2. Throttle handle pulled back 2 "clicks"
3. Hold down starter until engine turn over.
4. Let engine run for a few seconds and then set throttle handle back.
5. Once engine smooths out slowly push in the choke.

That last problem i am having is figuring out how long I should let the engine warm up. It seems like its really easy to stall out the engine when I first take off. After driving for a few minutes the engine is like a tank and I can even pull out of full stop in second gear with out it complaining.

What do you guys do with yours? How long do you let it warm up?

[53a1]

Hey Linx.

I don't know the exact answer but when I was a kid an old boss told me that 'no load' warm ups are good for old tech engines so he made me warm up the fork lift for 5 minutes under no load.

I think the idea is to warm up the block and water in the block then you can drive. The thermostat will open while your driving and let the rest of the water in. Choke is just to get it started and run smooth and you can shut it off when it idles on it's own. I don't think you should have to use the hand throttle.

Sounds like you're taking off immediately after start and I don't think that's a best practice.

[linx310]

Sounds like you're taking off immediately after start and I don't think that's a best practice.

I let it idle for about 3 mins or so. Maybe I should let it idle longer.

[wesk]

The throttle really doesn't come into play until the engine starts. Pumping it does nothing to help the start and leaving it open only adds air while you are trying to do just the opposite with the choke.

A normal start should be simply:
1-leave throttle closed.
2-Full choke
3-Press starter pedal
5-Operated throttle conservatively as soon as she starts and you have released the starter pedal.
6-Slowly open choke as engine idle smooths out.

Cold and been sitting start:
1-Operated handle on the engine driven fuel pump to ensure carb bowl is full
2-Repeat steps 1 thru 6 above.

If you are fortunate enough to be living up north here and have the dash mounted primer handle and are doing a cold start:
1-Operate handle on engine driven fuel pump to ensure carb bowl is full.
2-Using the dash primer pump make three squirts.
3-Then follow the steps 1 thru 6 in first section.

If you do not have the engine driven fuel pump with the handle this can be an issue when you let the jeep sit for months at a time. But if you have the dash mounted primer pump you can overcome the missing the engine pump handle.

[skyjeep50]

Engine warm up is key in one area, that the oil is flowing freely and doing its job of lubrication. That is one of the reasons to let an engine run for a short time before putting the engine under load. Oil weight comes in to play as well. Lighter grade oils have lower viscosity in low temps than heavier oils so as to move more readily in cold engines. So it is important to put in the recommended weight oil with seasonal changes. In warm ambient temperatures (summertime) there is not much need to "warm" the engine, the oil will be doing its job in seconds. However in very cold wintertime conditions, monitoring oil pressure is another way to gauge if your engine is ready to put under load. As peak oil pressure begins to sink, you know lubrication is flowing properly on a cold day. Idle does not warm an engine much and can waste a lot of gas. Light loading, such as moving off the mark slowly and driving at slow speeds for a short time is much more effective in warming the engine. I've been a pilot for over 30 years and air cooled aircraft engines are built different from Jeep engines, but sitting on the ramp behind a big prop blowing subzero air over the engine waiting for it to warm is a waste of time. Get the oil flowing, watch rpms, stabilize ignition and monitor engine oil pressure, then go. But of course, in aircraft, takeoff is full throttle, balls to the wall, nobody takes off at idle!

[wesk]

but sitting on the ramp behind a big prop blowing subzero air over the engine waiting for it to warm is a waste of time.

Not quite. A proper cylinder temp and at least an oil temp needle that starts to move upwards and oil pressure at it's normal range are still necessary in air cooled aircraft engines. The aircraft engine is warmed up between 800 and 1200 RPM after your oil pressure stabilizes. The cooling air flow across the cylinders is no where near the flow experienced by moving the aircraft forward at 120 to 160 MPH. Winter fronts are readily available for most singles to help regulate cylinder temps when the OAT is 20 F or less. There is a direct relationship between cylinder temps, oil temps and oil pressure but the trouble is most light single pilots don't have a cylinder temp gage.

Additionally air cooled engines have greater internal clearances then water cooled engines which facilitates a quicker flow of oil for them when cold. Also the rule in piston aircraft engines is any start below 40 deg F is a cold start. This usually means plug in sump and cylinder heaters or a pre-heat unit before starting these aircraft engines which by the way are significantly more expensive then old jeep engines. For example one of my customers in a Cessna 182 with a 230 HP 470 CI engine will pay me $900 for a rebuilt cylinder and 8 hours labor to change it. This equals the cost of a rebuilt exchange jeep L134 engine.

I have had my private ticket for close to 20 years and have been bending aircraft wrenches since 1966.

[skyjeep50]

Yep, air cooled engines are built different so the comparison to Jeep engines is not direct. We plug our aircraft in anytime the temps are below 40 degrees or so but when at a remote ramp and tie-down, sometimes without the assist of a ramp pre-heat, the pilot must start a cold-soaked engine (and sometimes the pevious pilot in our club forgets to plug it in). CHT is not always standard equipment. Arrow has it, 172 doesn't. Cherokees have a engine oil cooler plate, I don't think Cessnas do (at least we don't have one). Very cold engines in very cold temps will not warm to the same operating temps in the same time as if they are operated low power settings. Taxiing to the end of the runway helps in aircraft or running a Jeep slowly for a few miles is better than sitting at a standstill for a long period of time. At engine start oil temp will be at low level but will rise sharply as the oil pump starts working. Cold oil develops more resistance but as it's temp increases, pressure should start to modulate. Oil temp and oil pressure can be monitored in an aircraft but my M38A1 only has oil pressure. In really cold weather I've gotten to the end of the runway, done takeoff checks and the oil temp is barely off the peg, oil pressure is OK, waiting even longer will not help much. My point was that without any other indication, a pilot, or driver, could monitor oil pressure, be assured of critical engine lubrication with it "in the green" and with that higher power applications will be OK. One of the original questions posed was how long to warm up a cold engine - answer is it depends on many factors but my personal experience is that long warm up time while sitting still is not necessary.

[Cacti_Ken]

My M38 is pretty easy to start with a few pumps from the primer pump. I let it run a few minutes, back out of the building and pull the throttle out just a little and idle to the county pavement about 1200 feet in first or second gear. Then another 3/4 mile to the main hiway I'll go about 20-25 in third gear. By that time the engine is warmed up fairly good. And off I go. Of coarse down here the temperature is at least above 50 and close to 60 deg. before I go for a ride.

[wesk]

As stated above it best not to mix or compare apples to oranges. Best to keep the topic here on jeep so as not to get advice and numbers mixed up.

No one has bothered to define a

long time

but for jeep owners it is anywhere from 15 to 30 seconds in Texas to 2 to 5 minutes here in Wisconsin at 10 degrees F. Not what I would consider a long time by any stretch. But I do consider it time well spent!

[Cacti_Ken]

Yeah, my jeep doesn't fly.

[wesk]

It may be a good idea to mention that there's more of your jeep that needs a warm up then just the engine.

The gear boxes and axles will also be slow to allow gear oil flow and should be driven slowly and moderately at first on cold days. Having driven several of my jeeps here and in South Dakota in the winter I can attest to the unwillingness of the gear boxes, axles, steering gear and knuckles to move freely having a tremendous amount of drag for the first few miles.

[maeserik]

Wes you are right, during the last winter months because the snow and the salt on the roads ( corrosive for metal ) i hardly drives the jeep.
Only every two weeks i did a tour around the block and let it idle for about 15 minutes on a higher rpm to hold the batteries in condition.
Today i made a trip of about 40 miles. The first 10 miles i can't get the jeep faster than 35 - 40 mph. Lateron 45 mph was not a problem at all.
Back home, indeed the differentials and gearbox/transfercase feels warm.
Everything worked back the same as during summer !

Erik