Why Diesel Engines Are Difficult to Cold Start 

Wow, best ever! Thank you so much, that's a huge compliment!

Thank you very much!

Well thank you very much, that's quite the compliment my friend! I'm glad to hear you learned something, heck I learned quite a lot from making it too. The only downside now is that I don't have any video editing software to use as the one I was using suddenly stopped supporting my videos... Now it's down to finding a good setup and hopefully make the videos better even still!

I'm glad you are enjoying the channel! Nice pun too, 'deeper dive.' Best of luck keeping the ole' 7.3 going, and cheers from a fellow engineer!

Sure thing, I'm glad you like the video. Those graphics definitely take a while to put together! I saw you comment earlier, thanks for putting you knowledge out there, that too is much appreciated.

Thank you very much, I'm glad you like the animations! It definitely took a while, but I think they're pretty cool too.

The time and effort you put into your videos doesn’t go unnoticed.

Sure thing, I'm really happy to get the positive feedback, thank you!

Thank you very much! Some would argue grid heaters are better than glow plugs, at least there's only one of them to fail rather than 8. I might have considered putting a grid heater on the 7.3 after the first glow plugs went out in 2 months, but we won't talk about that... Nice truck by the way, the 6BT is indeed an awesome engine and those 2nd gen trucks are pretty cool looking too.

I'm definitely glad to hear you enjoyed the 'why' as well! I sure second guessed myself quite a bit as to whether or not anyone would appreciate the 'why.' Heck before making the video, I didn't even know the answer myself, and I learned a ton as well. It took writing a heat transfer program to figure things out, and the results seem reasonable too. Understanding that so much heat is lost to the block also explains why idi trucks even with a higher compression ratio are no better off at cold starts compared to a powerstroke. The swirl port adds internal surface area and hence increases the rate of heat loss as well.

15 f is not fun? :D here in Lithuania in Eastern Europe this year we had -15f -16f (approximately -26 -28 celsius)

@@Gaikiusalonas do you drive a diesel in this weather? In this weather some gasoline engines have trouble starting as well, am I correct?

@@larrywineman403 I drive a gas and diesel vehicles in Canada where temperature get down to -40'C and colder. Coldest temp I've ever personally seen was -62'C (-80'F) and my car (gas engine) started without being plugged in but it didn't like it very much. Both vehicles run fine but the Diesel is a little harder to start, remember that block heaters are your friend. I plug my diesel in at any temp below -20'C (-4'F) and I plug my gas engine block heater in at any temp below -30'C (-22'F). if either won't start at temps above those respectively without the block heater being plugged in, something is wrong or it's time for a new vehicle.

@@dman6377 thanks for the response! Very interesting- that’s some COLD WEATHER!!!

@@larrywineman403 I guess it is, but in northern Alberta, Canada it's just life. LOL

I'm glad someone appreciates all the math, hopefully it wasn't too boring... That's cool that you spend so much time as a strength of materials tech. That's where the foundation of great engineering feats reside. If you don't know your material, you've got nothing. Nice truck too!

Thank you! I'm glad to hear another fellow engineer has an interest in old diesels as well. What kind of diesel do you have?

@@Rnddiesel Right on, driving a sprinter van. It still has some hesitation when I start it (good weather) had all glow plugs replaced recently. (rather new to diesels, heard the trick of cycling the glow plug ingnition is one way to adresse that, also hearing that it will over stress the GP's)

@@emilegoguely4032 Good deal, a Sprinter van! I really don't know for sure what the best thing to do is, but on my truck in particular, the glow plugs stay on and cycling the ignition just causes the relay to turn off and back on slowing the warm up. I usually just wait 20 seconds or so after the wait to start light goes away, and it fires right up.

I'm glad you liked the video! My current tires are 305x70r16, it's a really oddball size. I don't really recommend them simply because they are so hard to find. I had the tread on one start to separate and had to replace the tire, the only one I could get had to be shipped from California! I'll probably replace them with 285x75r16 tires next, or I'll go back to the stock size just to keep the cost low.

@@Rnddiesel another aside,what's the lift on your truck ? I also have 97 7.3 , crew cab looks to be same ht. Pretty much stock tires. Any clearance issues with the tires on your truck? Thanks

@@brucebell7623 I believe my truck is stock and doesn't have a lift believe it or not. I'm running LT285x75r16 tires. I don't have any issues with them at all. Though in this video I had LT305x70r16's, even those didn't rub. I think the slightly narrower tire going to the 285 fits the old body style much better.

Yeah OD light flashing is definitely a transmission signal. Definitely avoid driving it for now if you can. First thing I'd do is check the transmission fluid. Shift through the gears with everything warm and on level ground and check the fluid. I've been fortunate to not have many problems in the way of transmissions so I don't think I'll be much help. Supposedly you can pull 'codes' from the transmission as well. Try hooking up an OBD II code reader and see if you get anything. If the trans is shifting hard, make sure your ICP sensor is plugged in all the way, though that would throw a check engine light on the dash. For whatever reason my 97 shifts hard when the ICP get's disconnected, but I don't know why. Also there's a big wiring harness on the transmission you can check. It's on the passenger side right above the pan and behind the downpipe I believe. With the plastic getting old it may have gotten disconnected or be dirty/ corroded. There's some special trick to pulling off the wiring connector without breaking it, you should be able to find someone online who's done it. I think my connector was broken when I pulled mine apart, but it still works fine. Cleaning it may solve your problem if it's dirty. It may be just a bad solenoid, sensor, loose wiring connection, but it could also be worse. It's just hard to tell with transmissions. Definitely make sure you have plenty of fluid first thought. Best of luck!

First off good luck with the purchase! If you can get a scan tool hooked up to it, though I don't believe 1995 was OBD II compliant, so you may have to use the paperclip trick or some equivalent means to look and see if there are any stored transmission codes (if automatic) or signs of misfires or bad sensors. Look, pretty much everything on the truck can be fixed by someone who know's what they're doing, even the engine can be replaced of course. Assuming you don't want to tear down the engine, here are some things to look for. Before even starting the truck, check the transmission fluid (if automatic). You want it to be light red in color, or slightly darker red is fine, but definitely be cautious if the fluid is burnt or black, this could be a sign of clutch slippage and overheating which means you're due for a rebuild. Of course transmissions go out, just reason the cost to replace one. If it's a good deal and just needs a transmission otherwise that you don't mind replacing, then go for it. At best its probably $2k for a stock rebuild transmission. Though be mindful if the fluid looks too fresh, ask the owner if they changed the fluid recently, they may be trying to hide some transmission problems, at least look at the transmission pan and look for any freshly cleaned spots that may indicate the pan was dropped recently. Check the engine oil, be cautious if it is below the fill mark, this may be a sign that the previous owner didn't maintain it so well. It's no big deal if it's a little low, I believe early model 94 7.3 powerstrokes had dipsticks originally calibrated where 10 quarts was full, but everyone after, 12 quarts was full. Basically if it's just a little low, that's fine it didn't damage the engine, just may indicate there are some other miscellaneous repairs you need to do otherwise from lack of maintenance, again, can be fixed just adds to the price. Check the turbo charger and intake system. Pull off the air filter and inspect the piping between the air filter and turbo, is it clean? Maybe just a little oily? Or does it have a layer of dirt and dust in it? Oil in the intake/ black sludge is perfectly normal, that's just a consequence of the CCV system venting blowby gasses into the intake. Definitely be concerned about dirt and dust though. If that stuff gets into the engine it'll act like sandpaper and significantly deteriorate the longevity of the truck, so if it only has 150,000 miles on it but has a dusted intake, odds are you're looking at an engine that is closer in wear to one with 400,000 miles, there's really no way to tell though. If it's really heavily dusted, that may be a good reason to walk away, use your sense, if it's just a very mild light dusting, it may be okay still. While you're there, take off the turbo intake boot if you can and the seller lets you. The goal is to inspect the turbo for wear. Grab the main shaft and see if you can push it in and out, if it moves excessively, that's a sign that you need to rebuild the turbo. Again not a deal breaker, just those turbos are a royal pain to remove and it definitely adds cost to rebuild it. At the very least inspect the compressor wheel, if it's severely mangled, yeah the turbo needs a rebuild. At least you need to replace that compressor wheel, as the bearings fail too, it can cause excessive play which allows the compressor wheel to contact the housing and really damage it. Check the truck for leaks, it's very common for these things to have leaks. The most common ones include leaking high pressure oil lines and a leaky oil cooler. These are no big deal, just more work and adds cost. I did the work myself and replaced my oil cooler seals for around $60 a year ago and haven't had any leaks from it since, it was just a very messy job! Specifically ask the current owner to not start the truck for at least 24 hours so you can see how the truck cold starts. If it cold starts rough it could be a sign of a bad glowplug system or worst case bad injectors. Make sure the guy doesn't use ether to start it! That's probably the one thing that I would just flat out walk away from the truck if I saw that. Ether can do some terrible damage, and if it were used in the past it can put micro fractures in piston that could grenade the engine in the next few thousand miles or sooner. If it won't start without ether, there are other things that are likely wrong with it. If it's above 70 *F the engine shouldn't have any issues cold starting even without operational glow plugs from my experience. Check blowby, this is just a visual inspection of the gasses leaking by the pistons, more blowby more wear. Take off the oil fill cap with the engine running, put the cap back on the oil fill hole upside down. If it just sits there and rattles a little bit but stays on, the engine is fine. If the oil cap is blown off or you can feel a significant pulsing from the gasses, your engine is shot, likely has a skip in one cylinder and needs to be torn down. Drive the truck and run it like you stole it. You want to make sure it's in good shape before you buy it. If it's severely sluggish and low on power, it may have bigger issues such as a weak high pressure oil pump, worn injectors (my injectors were very worn and the truck was so slow it was dangerous to turn left into traffic basically), a high pressure oil leak, or a bad Injection Pressure Regulator. If it passed the blowby test, and just drives slow, odds are it's fixable, though you're looking at anything from a simple set of orings as a fix to a new high pressure oil pump or injectors, so keep that in mind. During driving, unless it is chipped/ tuned, the 7.3 psd won't be 'fast' but it should be 'peppy.' It's not a high horsepower engine, but it does make decent torque and will get out of it's own way. It's definitely not a modern diesel, so don't expect a speed demon. Just think about how a 215 hp engine would pull a 6000+ lb truck. It's not 18 wheeler slow, still should have acceleration more comparable to an average pickup truck. For reference, in my experience a 7.3 psd will go 0-60 mph in about 15-16 seconds if in good shape. If it's closer to 18-19 second's for the 0-60 mph, it may have some worn injectors, but is definitely fixable, injectors run about $1,200 or so. Stand on the brakes if you can and be safe about it of course, let the owner know what you're going to do before you stand on the brakes. They should be pretty powerful, these are pulling trucks and should feel like they have powerful brakes. I don't believe any of them came with anti-lock brakes from that era though. Brakes are a common wear item of course, I redid all 4 brakes for around $350 doing the work myself and using new drums, disks, front calipers, wheel cylinders, and of course pads and shoes. Check the steering, is it loose? If you can look under the truck and inspect the tie rod ends, and other steering components while the owner turns the wheel side to side. Look for excessive play. You can definitely replace those steering components, I believe I priced a new front steering setup for maybe $300 excluding the cost of alignment. Everything else is going to be pretty standard, look at any weird wear patterns on the tires, bald tires, poor body panel alignment that could indicate it was in a wreck, which may or may not be a big deal depending on what your preference is. I really need to make a video on this sort of thing, I'll get there eventually. Anyway, best of luck with everything!

UPDATE. I looked everything over as you said and other than obvious steering and brake issues truck seemed solid. So i bought it and after I drove it for a few days a cold spell came through south Texas I noticed a massive oil leak. The front of the oil cooler leaking badly which i hear is a common oil leak from the orings. So i pulled off the cooler and of course the oil pressure regulator fell out of the housing into the oil bucket. LOL. After digging the pieces out i noticed the oil filter bypass valve is missing also. I didn't notice it fall out so I'm not sure if it was ever there. Well i just decided to order a whole new housing from Jegs that came with everything except the block heater. So I should be rolling again this weekend after parts come in. Thanks for the info and enjoying the channel.

@@chrisellis4140 Congrats on the purchase! Well I guess it was baptism by fire for you. Nearly every 7.3 gets an oil cooler leak, mine did, my friends' did, etc. It sure is a messy job, and I'm glad to hear you were able to get things figured out. I hope it works out well for you!

I don't see that being an issue, Cummins 6BT diesel engine basically did the same thing with the intake air grid heater. I don't know if your heat gun would really have enough power to heat all the incoming air, but if it works it's probably much safer than using ether with semi-functioning glow plugs.

@@Rnddiesel thanks small 3 cylinder

An oil pan heater wouldn't be as effective as a block heater in the coolant passage of the engine. The main reason is that the coolant naturally circulates around the outside of the cylinders, and during a cold start those cold cylinder walls are what saps a lot of the heat out. By heating the water on the other side of the cylinder walls you reduce the amount of heat lost during the compression stroke. An air intake heater would probably help. If you're curious look at the cold start mechanism typically used on the light duty Cummins diesel found in Dodge trucks. They have an air intake heater rather than glow plugs, so it's basically the same idea.

@@Rnddiesel very cool thank you for that. My buddy back east just picked up a 96 Dodge Cummins.

If by 'good stuff' you mean ether, then that's more like an addictive drug. You're taking a big risk of destroying your engine when you use it. It sounds like your glow plug system could use some work. Unfortunately it's probably a combination of bad glow plugs, bad relay, and/or bad under valve cover wiring harness. If it were your IPR valve you'd have more than just a cold start problem. I'll get off my soapbox, you do you, ether can destroy your engine in a heartbeat if you aren't careful.

@@Rnddiesel it's been like that for about 10 years. When it first started, I replaced all the glow plugs, then the relay. Couple years ago I had to replace the valve cover gaskets for a runnability issue. About a year ago, the CPS sensor, and the fuel bowl heater. All for different reasons but nothing hepled. I just gave up.

@@adielawson7179 I see, well aside from checking that the ECM is powering up the relay, you've basically covered the whole system. I'm sorry to hear you've had no luck, what a pain!

Haha that's hilarious. We don't often get snow down south, and it sure is welcome when it does. The whole state shuts down anyways when it does snow giving you a free day off which is pretty cool too!

Thank you I appreciate it, hope it was enjoyable!

I like your question, it's a good one but a tough one to answer. If you had a powerful enough heat gun, then technically it should be able to get the engine to start. It would be similar in a way to the Cummins method of starting cold where they use a grid heater mounted in the intake manifold to warm the air. I think the biggest issue would be getting a heat gun with the capacity to warm as much air as you need. By my basic calculations a 7.3 liter engine cranking over at 300 rpm would need around ~50 cubic feet per minute (CFM) of air. Glancing online, a typical gun produces around 10 CFM. With such a low flow, you'd need to use the highest heat setting. At that point you'd need to be very careful as to not melt any plastic that's in your intake manifold. I have doubt's as to whether it would actually work, but theory only goes so far in it's basic form. It might work better on a smaller diesel engine. None the less it may be worth a shot if you're careful about it. Let me know if you try it out and if you have any luck!

Rnddiesel Thanks for the reply. The reason I asked is I saw a vid from Russia where they used a flaming torch to heat the intake air. It worked but seems dangerous. Again thank you!

@@flyguy5941 I think I've seen that one too, crazy Russians I guess!

When I used to move heavy in the winter time we would use a propane torch to warm up the intake manifold. The engines would usually pretty much start right up after a minute or so dose of heat. It saved the juice from not using the glow plugs for cranking. They would smoke a bit but that's normal. Another trick my brother showed me was to put a rag with some gasoline on the air filter and after a few wifs the motor would start. A lot of old trucks would have a propane injection setup. They used a choke cable set so when you pulled the knob a metered blast of propane would be dispensed. Most people don't realize but you need a oil pressure to turn the fuel onto the injection system. Thinner oil in the winter time is your friend. If your oil is thick your oil pressure switch won't turn the fuel on the motor and it won't start. Another thing is if your voltage is too low the fuel pump won't turn on and then the truck won't start. so if truck is cranking slow which means the batteries are low which means the fuel isn't on. Old trucks with mechanical pumps are different story know pretty much because they don't have the oil pressure switch lockout.

Good idea to have a plug in oil heater ?

Indeed, the engineers do make it hard to work on things, but to be fair it's really the average car buyer who is at fault. If folks didn't want to have ridiculous acceleration and power in their commuter car while the EPA puts ever so strict emissions standards on vehicles, then the engineers could definitely make the vehicle easier to work on. Look at old cars from the 50's: no power steering, no AC, no heater, no windshield washing system, no radio, no emissions controls etc. Now all that junk gets crammed under the hood and makes is next to impossible to work on things these days without pulling half the car apart!

I appreciate your input! While I do technically have a degree, that only shows I have the ability to learn, doesn't mean I know everything. In principle it's simple to find the heat transferred if you know all the important parameters in the problem. You still run across the issue as to whether or not your model makes the appropriate assumptions. I think I did run the calculations and modeled the mass of air as a solid where conduction was the primary mode of heat transfer. The thinking there is that the process occurred so rapidly that there was no time for convection currents to form. It's been a while since I made the video so I don't remember everything I did. Ultimately I figured most folks would rather not see excessive complex math in a RU-vid video.

Yes indeed! It also works great for daily things like when you need to calculate how much peanut butter you can afford to fit on a sandwich and still have the jar last a week.

Jules3855 don’t watch the video then.