The chart below shows the most common questions asked by owners of Detroit Diesel® engines 6-71 Natural 4 Valve when trying to troubleshoot why their engines underperform.  It categorizes areas of possible malfunction, likely cause and recommended action to bring your new, rebuilt or used  Detroit Diesel® engine back to proper operation.  The chart will give you confidence when speaking with your Detroit Diesel® engine mechanic or ordering parts.  As a quick reference guide only, the chart must not be thought of as a substitute for the use of your Detroit Diesel® engine 6-71 Natural 4 Valve Owner's operating or service manual.

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Detroit Diesel 6-71 Usefull Information 

Our high quality parts for the Detroit 671 are guaranteed to work, and have been proven to last. We are proud to have served many satisfied customers over the years, and many have become customers for life. No annoying part numbers. No vague descriptions without pictures. Just straight forward pictures and information, with engines arranged by series and type, so you can be sure to see not only the part you need, but also complimentary products that could make your project a little easier. If you have any questions, our staff will be more than happy to give you more information, or help you find a hard-to-find part. If you would like more information, please scroll down to see more about our marine engine parts, locating your engines part number, diagnosing smoke coming from the engine and selecting the proper oil type.

If you need to find the serial number, look on the cylinder block. You will find a serial number that is similar to 6A18959. The first digit is the number of cylinders, so this example would be a 671 engine. In some older engines, the full engine size and series could be seen in the first three digits. For example, 671-RA63, the first three digits indicate it is a 6 cylinder member of the 71 series. Of course, if you are having any difficulty, call us and we will be happy to help.

The Detroit 671 is an engine that has found itself at home in many uses. In addition to the marine uses, you can find them in Ford F-9000 trucks, GM vehicles, tractors, farm equipment (including some Chamberlain, Allis-Chalmers, John Deere models), Eucilid Industrial Vehicles, busses (including Crown), as well as many military and government vehicles. Please note these vehicles are meant to be suggestions. Always double check the serial number, to be on the safe side.

To clarify, what we refer to as 671 on this page is the same as:

• GM 671

• Detroit Diesel 6-71


Lubricating Oil Information

Detroit Diesel 671 engines, like the others in the Detroit Diesel line, will probably spill some oil over the course of their use. This has earned the discharged oil the affectionate nickname of ‘slobber.’ With this in mind, replacing the oil is extremely important. However, only certain types of lubricating oil should be used. Listed here are some general guidelines about the lubricating system.

Oil Capacity: This engine uses 7 gallons of oil, which is 28 quarts. The engine should not be operated if the oil levels fall below 22 quarts.

Type of Oil: Be sure that you are using a high detergent lubricant made for heavy duty use. The type S-1 oil should be used, especially in warm or temperate conditions. S-2 may be used, as long as you are using fuel oils that have less than 0.5 percent sulfur. S-2 in particular should be used if the engine is constantly exposed to temperatures below freezing.

Viscosity: 10W-30 and 5W-20 should not be used in the 671 engine. The recommended viscosity is SAE 30. However, if the temperature is below freezing, other viscosities may be used. For example, from 0-30 degrees Fahrenheit, SAE20W can be used. For temperatures below zero degrees Fahrenheit, SAE10W30 can be used. This can help with the problem of starting the engine in cold temperatures.


Troubleshooting a 671T

Please note that these values are for four-valve, turbocharged engines. Values for other engines may vary slightly.

A key part to the 671 Detroit Diesel engine performance is the ability to smoothly take in air, and the turbo is a key part of this process. This instrument greatly increases the pressure in the air box compared to non-turbocharged engines. Listed here are some general maintenance items to check.

• Oil pressure should remain between 30 to 40 PSI when the engine is at full load. If it is too high or too low, consider changing the oil and checking the oil filter.

• The water should not be significantly higher in the turbo compared to the rest of the engine. If the water is 30 degrees F higher, then be sure to check the coolant passages on the turbo to make sure they are not clogged.

• The turbo should not vibrate excessively. If it is, the impeller or shaft may be damaged, and should be replaced.

• Poor performance can be tied to many problems, but a possible culprit will be leaks in the hoses, especially between the turbo and the blower. This can rob the entire unit of power.

• Overheating or overspeeding of the turbo can result in premature failure. This usually happens as a result of operating the unit at altitudes that are too high, or from having the wrong injectors in the engine. If you suspect the injectors are wrong, replace them with an injector that has a lower capacity.

If you do suspect that the turbocharger is giving you problems, we have a section here for removal and general maintenance of the unit. We also have a useful troubleshooting guide below that can help diagnose other problems with the engine. Of course, if you need any additional help, give us a call at 888-433-4735 and we will be happy to help figure out what the issue might be.


Servicing the Turbocharger on a 671 Detroit

Servicing the turbocharger can be a simple process when done correctly. Please remember to always note the location of any removed items, to properly replace them when done. This is intended as a general guide, and if there is any doubt then be sure to consult with an experienced Diesel mechanic before performing any servicing.

Step One: Prior to removal, drain the cooling system, and disconnect the oil and water lines. Next, disconnect the engine blower tubing, turbocharger air inlet and remove the silencer (if used.) Then disconnect the connection to the exhaust.

Step Two: Use a sling or rope to make sure the turbo is supported.

Step Three: Locate the supporting bracket bolts and remove them. The turbocharger can now be lifted from the engine.

Step Four: Remove any grease, debris and dirt from the outside of the unit. Clean and sludge deposits, and blow out air passages.

Step Five: To install a new one (or reinstall old unit), replace all of the gaskets before install. A rope or sling can then be used to lower the turbo back into place. Be sure to attach the turbo to the bracket first, before the bracket can be attached to the engine.

Step Six: After all of the tubes and inlets are reconnected, be sure to prime the lubricating oil. This can be done by disconnecting the oil inlet line near the top of the unit and pumping clean engine oil into the turbo. Then, reconnect the oil lines.

Step Seven: Refill the cooling system and be sure to check for any leaks when the engine is initially restarted.


Troubleshooting Smoke

Have a smokey Detroit 671? The following will give you a guideline of some common causes of smoke coming from the engine.

Black / Grey Smoke: The first thing to check with black or grey smoke is the exhaust. Remove the muffler and manifold and see if that resolves the issue. If this is not the reason, check the areas where air enters the system. For example, check the air cleaners, the ports for the cylinder liners, as well as making sure the area around the engine allows for fresh air. Besides the air, black or grey smoke can also be due to excess fuel entering the chamber, from improper setting of injector racks or improper timing of the injectors. Double check that the injectors themselves are functioning. It can also be caused by fuel that is too ‘heavy’ or the wrong grade.

Blue Smoke: Blue smoke is usually caused by fuel that is not burned when it should be. In other words, the fuel is pushed through the cylinder when fresh air is taken in. If this is the case, check the seals for leaks, especially around the blower. Also, be sure to check the oil lines and anywhere they are connected.

White Smoke: The most likely cause of white smoke is one or more misfiring cylinders. If you cut off the fuel supply to a particular injector and the white smoke stops, then that injector should be replaced.


Marine Engine Parts

At Diesel Pro, we have built our business around those who work in or around boats. So if you are looking specifically for marine parts, you have come to the right place. We specialize in providing parts for marine engines, especially the Detroit 671 (sometimes referred to as Gray Marine.) In other words, if you are the captain of a boat, or a marine mechanic, you have come to the right place. We offer many products that are essential, as well as a wide variety of products that commonly used on boats that aren't directly part of the engine, such as sirens, lights, and so on. You can also visit our 'Sea Water' option above to see impellers, heat exchangers, and water strainers, which are absolutely key to a boat engine running as smoothly as it should.