I see a lot of new threads asking about the 35d, and I get a lot of questions from folks outside of this forum, so I thought I would start a thread with information on the 35d and diesels in general. Diesels are foreign to a lot of people and are often misunderstood.
Some information here is based on personal experience and may differ from other member’s experiences in different areas.
Why get a 35d diesel?
Most people opt for the 35d because of fuel economy. Diesel engines are known to get better fuel economy than gasoline engines. Diesels are also known for their low end power and torque, and are good options if you plan to tow with it.
What does the 35d get for mileage?
In stock form it’s not uncommon to see 30+mpg highway, 25-27 combined, and 22-24 city. Obviously conditions, driving habits, and climates will affect this. Emissions deletes and tunes can increase economy BUT is not only illegal in most places, it will also void any factory warranty. This will be discussed later on.
Are diesels reliable?
It’s not uncommon to find high mileage diesel engines that will outlast the rest of the vehicle. In fact, diesels are known to be long lasting, high mileage workhorses. As with any engine, proper maintenance and care is necessary to prolong the life of your vehicle. Diesel engines are known to see well over 200k miles when properly cared for.
Common Terms Related to Diesel Vehicles:
DPF - Diesel Particulate Filter
Part of the emissions and exhaust system that is used to trap carbon deposits and soot from exiting your exhaust.
DEF - Diesel Exhaust Fluid
A fluid that is sprayed into the exhaust stream of diesel vehicles to break down dangerous NOx emissions into harmless nitrogen and water.
SCR - Selective Catalytic Reduction
System that controls the spray of DEF into the exhaust system.
EGR - Exhaust Gas Recirculation
A process of recirculating exhaust gasses back into the engine to burn off any unburnt fuel.
Cetane
Simply put, cetane is a chemical compound found naturally in diesel, and it ignites easily under pressure. Higher cetane numbers mean the fuel essentially ignites easier and faster, allowing for more efficient burning of fuel and more power output.
Engine information:
The US market F15 35d uses the N57TU variant of the N57 family. The N57 family has single, twin, and even triple-turbo configurations, but the US market only received a single-turbo configuration. The main difference between the Euro N57 and N57TU is in the emissions systems, the emissions system is specifically designed to comply with the current US market emission regulations. The predecessor to the N57 is the M57, which was found in the E70 35d and various other BMW models.
N57TU
3.0L inline six, single variable-trim turbo
255hp @ 4000RPM, 413ft lbs @ 1500-3000RPM
0-60: 6.0 secs (BMW claimed)
Because of the global warming fight and decrease in interest in diesels, BMW stopped offering the diesel in the US after 2018.
Common misconceptions:
Diesels are bad mkay? They are loud, they stink and are bad for the environment:
Not true. When it comes to passenger vehicles most of us are used to the old loud diesel pickup trucks that puffed out black smoke and stunk the entire yard up. That’s simply not the case anymore. With today’s noise insulation and emissions systems you wouldn’t even know you’re standing next to a diesel while it was running. Older diesel trucks did not have emissions systems like they do today. While conditions and results do vary, studies have shown that newer diesel emissions can emit less carbon dioxide than gasoline engines.
Diesel fuel goes bad really fast:
Not true. Gasoline when properly stored has a typical shelf life of 3 months. Diesel fuel when properly stored can last up to 12 months. The issue is diesel engines are more susceptible to running poorly once fuel quality is compromised. Some fuel stations don’t see regular diesel traffic so the fuel may sit in their tank for long periods of time. Fuel stations may also not fill diesel tanks regularly or keep them topped off if they don’t see a lot of diesel usage, so those tanks sit with empty space which can build condensation. If water gets in your fuel, regardless of the fuel type, it will cause issues. Regular vehicle use and choosing fuel stations that see regular diesel traffic will help to mitigate fuel quality issues.
Diesels are not good in cold climates:
Partially true. Diesel fuel is prone to what we call “gelling”. When diesel fuel gets too cold, it thickens and turns to a gel, making it not flow through lines, clog fuel filters, and render the engine useless until it warms up, but there are ways to help prevent this. To mitigate this, fuel stations in cold climates have different blends of diesel fuel. We will talk a more about fuel types later on. Additionally, BMW uses a heated fuel filter to help aid in keeping fuel in liquid form. I personally have been parked outside in -20 degrees F overnight for multiple nights and have not had any issues.
Diesel fuel is more expensive:
Partially true. Diesel fuel prices fluctuate a lot, but seldom get much more than premium gasoline prices. Even when they are higher than premium prices, you’re usually getting better fuel economy and it balances out.
Diesel fuel is hard to find:
Partialy true. It may be harder to find some types of diesel in small towns or small fuel stations, but most major fuel stations will carry diesel fuel.
Diesels are expensive to maintain:
Partially true. While diesels do require a little more maintenance compared to gasoline engines, this does not always mean they are more expensive. As with all vehicles, proper maintenance and care will keep your maintenance costs down.
General Information:
Fuel types:
Diesel generally comes in two types, or numbers, No. 1 and No. 2. Some areas may have No. 4, but this is for low-speed engines and not for passenger vehicles.
No. 1 is not usually used in passenger vehicles because it has less energy and lubricating components and is more expensive, but it’s better for cold climates as it has little to no gelling when the temperature gets cold (32deg F and lower). While it’s not usually recommended to use No. 1 on passenger vehicles, it can be done if that’s your only option. When using No. 1 fuel, be sure to run lubricating additives, which are discussed later on.
No. 2 is what is commonly found at most fuel stations. It has more energy and lubricating components than No. 1, and is cheaper, but it is prone to gelling at cold temperatures. To help mitigate gelling, fuel stations in cold climates will offer a winter-blend, which is a blend of No. 1 and No. 2, to help lower the temperature before it starts to gel. In my experience, winter-blends are usually fine until you start getting into sub-zero temps, BUT that’s just my experience. If you know you will be seeing sub-freezing temps you can run additives that help prevent gelling, or if you already have gelled fuel you can use Diesel 911, which is an additive that will turn gelled fuel back to liquid form in an emergency.
Some fuel stations also offer tax-free off-road diesel. This is for use by government or commercial vehicles and is not to be used by passenger vehicles unless you have an approved exception. This fuel is dyed to be a different color than regular diesel so it is easily identified. If you ever get stopped and get your tank dipped and they find off-road diesel when you’re not authorized to run it, you will be fined.
Biodiesel is a renewable, biodegradable fuel manufactured domestically from vegetable oils, animal fats, or recycled restaurant grease. When mixed with conventional diesel fuel it is supposed to be cleaner burning and release fewer toxins into the environment. Fuel stations may offer a biodiesel blend typically labeled as B5, B7 or B20. The number represents the percentage of biodiesel mixed with conventional diesel.
Sounds great, right? Maybe not. Biodiesel is a controversial subject and most manufactures do not recommend it as there are claims it damages components and engines. BMW says we can run up to B7, or 7% biodiesel blend, but recommends not going higher than 5%. You will also see a decrease in feul economy when using biodiesel blends.
Why is biodiesel bad? It’s a dirty fuel. Biodiesel will clog filters, lines, injectors, and other components faster than conventional diesel. Not only is it a dirty fuel, but it’s said to be corrosive over time. Unfortunately the federal gov’t has created credits and incentives to get states to offer more biodiesel, and depending on where you are you may not have a choice but to run it.
Diesel Fuel Station Pumps:
Some diesel pumps have a nozzle size that is larger than regular gasoline pumps to ensure that you don’t fill your vehicle with the wrong type of fuel. The smaller gasoline nozzles aren’t large enough to release the mechanism to allow you to insert the nozzle in your filler hole. Not all fuel stations have these, but they are becoming more and more common. If you find yourself at a pump that doesn’t have the larger nozzle size, first ensure you are indeed at a diesel pump, and if so you can finagle the nozzle around or use something to press the release as you insert the nozzle.
Some pumps have a really large nozzle that is meant for commercial trucks and it won’t fit into your filler hole. They make an adapter for this very situation should you find yourself at a pump that only has the commercial sized nozzles, and it’s a smart idea to pick one up and keep it in your vehicle. The downside of this adapter is you have to hold the pump handle and manually control the flow of fuel, but it can save your butt when you need fuel and don’t have the correct pumps.
You’ll notice that diesel pumps are generally messy because diesel does not evaporate like gasoline does, and it is rather smelly, so if you get fuel on your hands the smell tends to linger for a long time. Keeping disposable gloves in your vehicle to use while fueling is a great way to keep your hands clean.
Fuel Additives:
There’s a lot of information in the forums regarding additives. Additives can be a controversial subject as some people say they are fine, some say they may void warranties. I personally have always used additives and have not had any issues. Additives can offer many benefits and can vary with what kind you use. The most popular additives give a boost in cetane (which is a lot like octane in gasoline), prevent water condensation, and they also help with lubrication. Diesel fuel, as contradictory as it sounds, is naturally a dry fuel. There’s not a lot of lubrication qualities to diesel, so using additives that add lubricants to the fuel help keep fuel pumps, injectors, and cylinders lubricated and operating smoothly. No. 2 diesel does have lubricating components added to it already, but the little extra from additives always helps.
Hotshots Secret is one of the more popular brands of additives. Hotshots EDT and Extreme Diesel are very common for people to use.
Diesel Maintenance:
Diesel maintenance is a little more involved than gasoline engines. You have your typical maintenance like oil changes, filter changes, coolant flush, etc. that for the most part follow the same intervals as gasoline engines, but you also have additional maintenance like fuel filters, glow plugs, and emissions that need to be addressed.
Fuel Filters: According to BMW, fuel filters should be replaced at least every 40k miles, but they recommend every 20k. Some people have made it a habit to replace them every other oil change or every 3 oil changes. This is important as diesel fuel tends to be “dirty” and can start to clog up filters. Filters are relatively inexpensive and not overly difficult to replace.
Glow plugs: Diesels don’t use spark plugs, instead they use glow plugs that heat the cylinders in order for the fuel to ignite. Diesel fuel has a flash point of 126-205 degrees F. There is no spark used to ignite the fuel, only heat. Air is compressed until it heats above the autoignition temperature of the fuel. Once it reaches temperature, the fuel is injected and BOOM! You get ignition. When the engine is cold and you go to start it, the glow plugs heat up the cylinder to help with that first few revolutions to get the engine running. Once running, the heat in the cylinders is enough to keep it running and the glow plugs shut off. Over time the glow plugs wear out and you need to replace them. Most people seem to get about 70k miles before needing to replace glow plugs, and they cost roughly $30/ea for replacements.
DEF and Emissions:
The emissions system requires the use of DEF, or Diesel Exhaust Fluid. This is easily found at any auto parts store, Walmart, and most gas stations. The lifespan of a tank varies a lot depending on driving conditions and habits, but it’s generally reported to last 10-20k miles. The vehicle will let you know when the tanks are getting low, usually with around 1000 miles until empty. Do not top off your DEF until you get the warning light or it may throw off the ECU's reading and cause the vehicle to go into limp mode or not start until the system is reset. Once you get the warning be sure to fill them up as soon as you can. If you don’t and the tanks run out, the vehicle will go into a limp mode, or limited power mode, until they are filled.
DPF Replacements and Regeneration Cycles:
A lot of people are concerned about DPF systems getting clogged or going bad, as it can be an expensive repair. It's no secret that the DPF can get clogged with carbon and is likely going to need replacing at some point in the life of the vehicle. This normally happens when reaching higher mileage, usually +100k miles, but depending on your driving conditions or habits it can happen sooner.
Most diesels, including BMW, have what is called the DPF Regeneration Cycle. This process increases your exhaust temperatures and helps to burn off the soot that builds up in the DPF. The process is controlled by the vehicle and there are a few conditions that need to be met before the regeneration process starts, but simply put this process starts after 20-30 minutes of highway speeds (+50mph) and takes about 10-15 minutes to complete. People that rarely see highway speeds, or may not spend more than a few minutes at highway speeds may not enter the regeneration process and may see the DPF become clogged and need replacing more frequently. It's always best to ensure you reach highway speeds for at least 30 minutes once a week to complete the regeneration process.
There is still your typical routine maintenance that needs to be done, just the same as a gasoline engine. Timing chains, coolant flushes, brake fluid flushes are really no different in a diesel vs a gasoline engine, and should be followed in accordance with BMW service intervals.
Deletes and Tunes:
Most people that are thinking about diesels ask about deletes and tunes. Emissions systems are very restrictive, so removing those systems can open up a lot of power potential. Emissions are also MPG robbers, so removing them can give you a good increase in fuel economy. Removing emissions also mitigates carbon buildup that was mentioned previously in maintenance, prolonging the life of your engine. While all of these may sound great,
it is federally illegal to remove or tamper with vehicle emissions systems. If you live in a state with regular emissions testing, a delete and tune will almost certainly cause you to fail the test. The EPA has been really cracking down on deleting emissions and has been going after shops offering these services, so a lot of US based shops have stopped offering them.
Because of the nature and legalities of this topic, it is not recommended to remove your emissions systems. If you should chose to, any legal ramifications fall upon the vehicle owner.
Everything you need to know about deletes and tunes:
https://f15.bimmerpost.com/forums/sh....php?t=1525210
Towing with the 35d:
The 35d is a workhorse considering it is an SAV. The engine has plenty of power and will happily pull heavy loads without any fuss, however, two limiting factors in its ability to tow extra heavy loads are the brakes and unibody chassis.
Below are the towing specs for the F15 35d.
Towing capacity – 6000 lbs
Max tongue weight – 600 lbs
There are multiple receiver options available for the F15, to include the M Sport models. Most have the ability to plug directly into the vehicles wiring system and sway control can be coded to help keep loads under control. Keep in mind your receiver selection is also going to have its own capabilities. While these are usually higher than the vehicles capabilities, whichever is lesser is what you need to stay within. For example, my Stealth Hitch receiver has a rating of 8,000lbs pull weight and 800lbs tongue weight, but the vehicle is less than that and therefor I must stay within the vehicles capabilities.
Diesels and cold weather:
It’s no secret that diesels don’t like cold weather, but that doesn’t mean they are bad for cold climates. BMW uses a heated fuel filter to aide in keeping the fuel in liquid form, but there are other measures you can take to help mitigate cold weather problems.
As mentioned previously, diesel No. 2 starts to turn to gel below 32 degrees F. Running winter-blend fuels in the cold months is recommended, and most fuel stations will automatically make the switch to winter-blends at their main pumps. Running additives in your fuel can help further lower that gelling temperature limit, and keeping Diesel 911 in your vehicle for gelling emergencies is always a good idea. Additionally, parking your 35d in a garage or out of the wind can also help keep fuel from easily gelling.
Block heaters help keep the engine block warm when the vehicle is not in use to aid in easier startups. Block heaters used to be a fairly standard thing on diesel engines, but newer diesels no longer have them. There are aftermarket block heater kits that you can install if you require.
On those really cold nights some people will place heated blankets over the engine or under the fuel tank, and sometimes try to cover the bottom of the engine with heated blankets as well. This really isn’t done unless it gets down into double digit sub-zero temps and are parked outside for long periods of time.
Recalls/Known Issues:
Timing Chain:
It's common for the N57 to need a timing chain replacement over ~120k miles. This is thought to be a result of the longer oil change intervals recommended by BMW. Symptoms of a dying timing chain are rattling and knocking noises coming from the rear of the engine (timing chain is in the rear of the N57). If the chain is not replaced before failure it will damage the engine, as it is not a non-interference engine. Chain failure mill likely also cause damage to the oil pump and system. Shorter oil change intervals (5k miles) is said to prevent/prolong chain failure.
Carbon Buildup:
Carbon buildup is one of the biggest concerns with a lot of folks considering diesels. Emissions systems reroute exhaust back through the engine to burn off remaining unburnt fuel vapors. This causes carbon buildup in your intake manifold and head restricting airflow, which can lead to decreased performance. The N57 was redesigned and is much better at reducing this buildup compared to its predecessor, the M57. Most shops offer a carbon cleaning service and will go through everything and clean it out. Cost can vary, but from what I have seen it’s generally around $1-2k. How often you may need carbon cleaning varies. Vehicles that are used for short commutes tend to need cleaning sooner than vehicles that are used for longer commutes. Driving habits will also play a big role in carbon buildup. Typically people see the need for carbon cleaning around the same time glow plugs need replacing, every 70k miles or so, but again, that will vary. The N57 has shown to not need this done often, if at all, and most folks that have performed it themselves have found the buildup was not bad and cleaning was probably not needed. With that said, it is still something that comes with owning a diesel.
Fuel Pump Failures:
The N57 family of engines has a known issue regarding Bosch CP4 High Pressure Fuel Pump (HPFP) failures. When the pump fails, the gears inside tend to explode, sending small shards of metal through your fuel system. These shards can get into your injectors and cylinders causing catastrophic damage. BMW has recently release a recall for all diesel vehicles affected, so hopefully this will no longer be an issue. If you’re looking at purchasing a 35d, inquire if the vehicle has had the fuel pump replaced, and if not, run the VIN through the BMW Recall site to see if it’s one of the affected vehicles.
HPFP Recall Information Thread:
https://f15.bimmerpost.com/forums/sh....php?t=1847232
EGR Cooler Leaks:
The N57 family of engines had an EGR Cooler recall come out in 2018 for coolant leaks in the EGR Cooler. When coolant leaks into the EGR system it mixes with the carbon and soot in the exhaust, causing damage to components and potential fire risks. If you’re looking at purchasing a 35d, inquire if the vehicle has had the EGR Cooler replaced, and if not, run the VIN through the BMW Recall site to see if it’s one of the affected vehicles.
EGR Cooler Recall Thread:
https://f15.bimmerpost.com/forums/sh...php?t=15523739
EGR Valve Failures:
The EGR Valve warranty has been extended by BMW for the N57T engine to 10 years/120k miles. The EGR Valve may fail, causing the vehicle to run poorly and receive engine warning lights. This was not a recall and the valves were not required to be replaced unless the vehicle was experiencing issues, but it's something you may want to inquire about if you are looking to purchase a 35d.
EGR Valve Warranty Information:
https://static.nhtsa.gov/odi/tsbs/20...52288-9999.pdf
Emissions, NOX Sensors, DPF/SCR Replacements:
This is not specific to the N57 or the F15 chassis, but is a common issue with any diesel with newer emissions systems. Eventually components get clogged up and begin to fail, especially on higher mileage vehicles. Emissions systems components can be expensive to replace, and most people opt to just remove them all together once they start seeing problems with them. As stated in the Deletes/Tunes section,
removing the emissions system is illegal and you will need to be familiar with your local requirements.
F15 Chassis issues not specific to diesels:
Control Arm and Sway Bar Bushings:
A lot of F15 vehicles have had issues with the control arm and sway bar bushings going bad on the F15 chassis. When the bushings go bad you will get vibrations in the front suspension. Search the forums and you will find plenty of threads regarding the issue.
Motor Mounts:
Motor mounts getting weak and causing engine vibration is somewhat common. Search the forums and you will find plenty of threads regarding the issue.
Front Driveshaft Play:
The front driveshaft can develop play in the splines where it slides into the front differential. Too much play can cause the shaft to wobble, causing premature wear on the u-joints leading to the joints failing and the driveshaft coming lose and causing extensive damage under the vehicle. This is not very common, but happens enough to gain some attention. You can test the driveshaft by raising the vehicle and wiggling the driveshaft by hand. It should have zero side to side play where the shaft enters the front differential.
There is a forum member that offers a upgraded driveshaft that addresses this issue.
https://f15.bimmerpost.com/forums/sh...2&postcount=31
As I think of more information to add I will update this thread. Please, feel free to ask questions in here.