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Maintaining Your Diesel Engine in the Summer

Maintaining Your Diesel Engine in the Summer

1. General Checkover

A quick visual inspection can go along ways to prevent issues from popping up and causing more issues down the road. This would also be a good time to check all of the lights around the truck. Have an assistant sit in the truck and apply the brakes, turn signals, and put the transmission in reverse to be sure all lights are working properly. It is surprising how many trucks we get in for service that have bulbs that are out. If you don’t mind crawling under the truck, it would be good to get out the flashlight and look for any oily residue or buildup or leaks that could be showing up.

2. Fluids

Let’s pop the hood and work our way systematically around the diesel engine bay. Summertime brings the bugs and other road debris and this might be a good time to add some washer fluid that will help clear that bug debris and keep the windshield clean. Everytime you drive your truck, you have to look through that windshield and having it clean is often overlooked. Wiper blades often get the blame for not cleaning the windshield, but the buildup of oils and other airborne contaminants can prevent the wipers from being able to do their job effectively. Using a high quality glass cleaner will help keep visibility clear.

Check the brake fluid, if it is low, it could be an indication that the system needs to be further looked at and could indicate other issues such as worn brake pads or possibly even a leak.

Check power steering fluid level, not only is it responsible for the power steering, but also a critical part of the brake system providing assist on Duramax diesel trucks that use a hydroboost system instead of a vacuum assist as found on most passenger vehicles.

Pull the transmission dipstick as well if the truck is up to operating temperature. The truck should be idling and the transmission in Park when checking the fluid level. Even though there is a “hot” and “cold” range, we are looking for the fluid level to be at the bottom of the Hot range.

Check the engine oil level as well. There are plenty of opinions on how often it should be changed and no doubt, plenty of supporting arguments to back it. Ultimately, the best way to determine the remaining life of the diesel engine oil is to have it tested. We make this easy for you with our Fluid Analysis Kit. Not only will this give you an indication of the remaining life of the oil, it will also give you an in depth look at the condition of the diesel engine with a comprehensive and easy to read report.


The coolant level can be easily checked at a glance on your Duramax diesel by looking at the coolant surge tank. The tank will indicate where the level should be. Be sure not to remove the cap until you are certain the vehicle is completely cooled down. The condition of the coolant can be hard to tell visually but, just like the oil, it can be tested using just a small sample and our Coolant Analysis Kit.

The drive axles are an easily overlooked part of the driveline. While you have a dipstick or some type of low level indicator on the dash for things like engine oil and washer solvent, the drive axle is easily forgotten about. Checking the fluid level is easy by simply removing the fill plug and ensuring the fluid level is at the correct level. Rule of thumb is that the fluid would run out of the fill hole while sitting on level ground for a properly filled unit. While proper level is critical for long life, changing the fluid periodically is just as critical. Many rear differentials are equipped with a traction lock device that uses small clutch plates to engage under certain conditions and the fluid quality and condition is critical to proper function. When servicing the rear differential, be sure to use a quality fluid that contains the correct additive for a limited slip or an additive can be used. If you have a four wheel drive truck, the front differential would be checked the same way.

If you drive a two wheel drive truck, just skip right on past this part. The transfer case is not something you would maybe think about in the summer months as typically most people use 4wd only in winter months, but it has to work just as hard in the summer even if you spend most of it in 2wd. Changing the fluid every 50,000 miles is going to ensure long life and we recommend using Merchant Automotive Transfer Case Fluid. Our proprietary fluid is specifically formulated for use in all modern transfer cases to combat wear, prevent annoying slip yoke clunk, reduce clutch chatter and improve engagement.

3. Filters

The summer heat puts a demand on all areas of the truck. Depending on what year the truck you have, it may have cabin air filters. Dirty cabin filters are going to restrict airflow from the vents, blocking that nice cool air! They can also contribute to foul odors inside the truck. We have replacement cabin filters ready to ship!

The engine air filter is something that should be checked every time the diesel engine is serviced. Replace it if it's full of debris, but even if it looks clean, it could still be restricting valuable air flow into the engine. Replace it every 20,000 miles even if it doesn't look dirty to help ensure maximum life from your Duramax diesel. We have ACDelco air filters in stock for immediate shipment

The fuel filter is one of the most critical things that should be maintained on any diesel engine. The filter is the last line of defense for the critical components of the fuel injection system against water, dirt, algae, and any other debris. The Duramax fuel systems run at pressures well above 20,000 PSI and even the smallest particles can wreak havoc at those pressures. Changing the filter every 10,000 - 15,000 miles is good practice. Pick up a replacement fuel filter today!

4. Tires

It is common for tires to lose air pressure over time if not checked regularly. While most modern trucks do have a tire pressure monitoring system (TPMS) you will want to check each tire periodically if you do not have TPMS. One of the biggest causes of tire failure is over or under inflation. Especially critical when towing or hauling additional loads in the bed. Don’t forget to check the spare tire! It is often forgotten and neglected until you need it. It’s not a bad idea to break out the tools that come with the truck and lower the spare tire. This allows you to be sure that the winch system is still functioning and not rusted up as well as take a quick look at the spare tire to ensure it is not damaged and will be ready if you need it. Spray some lubricant in and around the spare tire winch to help prevent any corrosion that could render it useless when you need it the most. This also of course ensures that you do have the tools in the truck needed to lower the spare.

5. Trailering and Towing

Summer is the time for camping and other towing needs, likely one of the main reasons you bought a diesel in the first place! Inspect your hitch carefully against any rust or signs of fatigue, safety chain attachment points, and the trailer connector. That is a common place for corrosion build up as well as dirt and bugs to populate which would prohibit a good connection to your trailer. This could cause faulty lighting, or erratic trailer brake operation.

6. Additional Items

Overtime, dirt, bugs, road debris and other things can plug up the fins in the cooling stack. This all restricts the critical airflow through the coolers and will prohibit the coolers from doing their job effectively. Symptoms would include higher coolant temp, transmission temp, and reduced air conditioner cooling. What would not be as obvious but still an issue is higher charge air cooler temps. We show you just how bad these can get in this quick video. How-to properly clean the cooling stack in a Duramax truck - Mechanics Minute

You can help prevent unexpected repairs and help prevent breakdowns with just a little effort and preventative maintenance. Merchant Automotive is here to help you out with your Duramax Diesel. Specializing in the Duramax since the company's inception, and working on them since they first hit the market in 2001, you can count on Merchant Automotive to be the trusted experts for all things Duramax! 

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