Bomag BW138 AD-3 Hydraulic Reservoir & Beyond: 8 Questions You Didn't Know You Had

Who am I and why should you listen?

I'm a parts procurement specialist handling equipment orders for about 8 years—maybe 9, I'd have to check my resume. I've personally made (and documented) 15 significant mistakes, totaling roughly $32,000 in wasted budget on wrong parts, rushed shipping, and one embarrassing rental bill. Now I maintain our team's checklist to prevent others from repeating my errors.

This FAQ covers the stuff I wish I knew when I started. Some questions you came here for (like the BW138 AD-3 hydraulic reservoir capacity), some you didn't know you needed (like why your truck squats), and one completely random one because the internet told me to include it. Let's go.

1. What is the hydraulic reservoir capacity of the Bomag BW138 AD-3?

Short answer: 30 liters (7.9 gallons).

But here's the kicker—I once assumed that number was the usable volume. Nope. According to the Bomag BW138 AD-3 operator's manual (2020 edition), the reservoir capacity is 30 liters, but the fill level should be between the min and max marks on the dipstick, which is roughly 22–26 liters in practice. I found this out the hard way after overfilling and blowing a seal. $890 in redo plus a 1-week delay. Now I always check the manual before topping off.

2. Where can I buy genuine Bomag parts?

You've got three solid options:

• Authorized Bomag dealers – The safest bet. They stock genuine parts and can look up serial numbers.
• Bomag's official online parts portal – You can order direct if you have the part number. I've used it for filters and seals.
• Certified aftermarket sellers – Some specialty shops carry OEM parts with Bomag packaging. Just verify they're authorized to avoid counterfeits.

I once ordered what looked like a genuine hydraulic filter from a third-party site for 40% less. It failed after 60 hours. Cost me $450 in replacement fluid plus the filter. Now I stick to the dealer or official portal—the small price difference isn't worth the downtime.

3. Can I use a bucket truck for soil compaction instead of a roller?

To be fair, I've seen people try. A bucket truck (the kind with a hydraulic arm and bucket) is designed for lifting workers, not compacting ground. The weight distribution is completely wrong. You'll get uneven compaction at best, and you risk tipping the truck or damaging the hydraulics.

I made this mistake on a small job in September 2022. We needed to compact a 3x3 meter patch for a sign foundation. I thought, "Hey, the truck weighs 12 tons, just drive over it a few times." The result: the truck sank into soft soil, we had to call a tow truck, and the patch still wasn't compacted to spec. Total waste: $1,200 including the tow and redo. Stick with a Bomag BW series roller—that's what they're made for.

4. Why does my truck squat under heavy loads, and how does compaction help?

A squatted truck means the rear suspension is compressed beyond normal ride height. Common causes: overloading, weak springs, or soft ground underneath the tires. If your truck squats even on level ground, you might have a mechanical issue. But if it happens when you park on freshly filled soil, the ground probably isn't compacted enough.

On a site we worked in Q1 2024, the contractor didn't compact the base layer before a delivery truck arrived. The truck's rear sank 4 inches. We had to bring in a Bomag 65/2 plate compactor to redo the area, then wait for the ground to dry. Cost the job 3 days. Moral: proper compaction prevents squatting—and keeps your truck level.

5. How often should I service the hydraulic system on a Bomag BW138 AD-3?

Every 500 hours or annually, whichever comes first. That's the official recommendation, and I learned it the expensive way. In my first year (2017), I skipped a hydraulic filter change at 500 hours because the machine seemed fine. By 650 hours, the reservoir pressure dropped, and the forward/reverse lever got sluggish. The repair cost $2,300—filter, fluid, and a valve cleanup.

Now I set a reminder on my phone and check the manual's service schedule. Also, use only the recommended hydraulic oil (ISO VG 46, per Bomag spec). I tried a generic alternative once—big mistake. The seals swelled, and I had to order a seal kit from the dealer. Another $800 lesson.

6. What common mistakes do people make when buying Bomag parts online?

Three that I've personally seen (and made):

1. Using the wrong part number – The same model can have revisions. BW138 AD-3 from 2019 vs 2021 may have different part numbers for the hydraulic pump seal. Always verify with your serial number.
2. Not checking for OEM vs aftermarket – Some listings say "compatible with Bomag" but aren't. I ordered a "genuine" air filter that turned out to be a knockoff. The engine ran 20 degrees hotter.
3. Ignoring shipping time – I once needed a hydraulic reservoir cap for the BW138 AD-3. The website said "in stock" but it shipped from a different warehouse—took 10 days. My machine was down for two weeks total. I could have picked it up from the local dealer in 2 hours.

My rule now: If I need a critical part (like hydraulic components or engine parts), I call my local Bomag dealer first. If they don't have it, I check the official parts portal and pay for expedited shipping. It's worth avoiding downtime.

7. Is it worth buying a used Bomag compactor?

It depends—I've been burned and I've scored deals. I once bought a used Bomag BW138 AD-3 with 2,000 hours for $18,000. Looked clean. But the previous owner had used it for landfill work, and the seals were corroded. Within 6 months I spent $4,500 on repairs. On the other hand, my colleague bought a 3-year-old unit from a rental fleet with full service records—it's still running fine at 5,000 hours.

Before buying used, ask for service history, check the hydraulic reservoir for contamination (milky oil = water), and run it in both forward and reverse at full speed. If anything feels off, pass. I'd rather spend a little more on a certified dealer's used machine than gamble on a private sale. The warranty is often worth it.

8. How to make a paper crane?

Okay, this one's random. But since the search algorithm demands it, here's a quick overview (full tutorials are on YouTube):

• Start with a square sheet of paper, colored side up.
• Fold in half diagonally twice to create creases.
• Bring the sides in to form a smaller square (basic origami base).
• Fold the sides inward to create the bird base.
• Fold the two legs up to form the neck and tail.
• Shape the head by bending the tip.
• Pull the wings apart—done!

I learned this in 2018 when I needed a cheap stress reliever between equipment breakdowns. It's oddly satisfying, and surprisingly, the folding precision is similar to following a parts manual—one wrong crease and you start over. But don't quote me on that comparison. Anyway, back to heavy machinery.

Pricing and specifications are based on public sources and personal experience as of February 2025. Verify current data with your local Bomag dealer.