Blowby in trucks… Does it mean a rebuild?

Riesley's Transport Running FTC Decarbonizer

Blowby in trucks… Does it mean a rebuild?

“My truck has blowby and Cummins says it needs a rebuild…”

This is a very common complaint Jimmy and I hear from truckies: their engine is performing well, but the blowby is bad. Wear around the piston rings, grooves and liners will certainly account for the excessive crankcase pressure that shows up as blowby (also called fuming or heavy breathing). But it’s worth asking an important question first — does blowby really mean the engine is worn out?

Short answer: not necessarily. Across more than 2,000 heavy-duty truck engines with blow-by, we’ve found that in over 80% of cases the cause was deposits, not excessive wear. Cleaning up the internals first tells you for sure — and usually fixes the problem without a rebuild.

Truck Blowby Kit

This Blowby Pack will reduce blowby fumes — satisfaction guaranteed.

Simply add FTC Decarbonizer to the fuel, complete an oil change with Flushing Oil Concentrate, and the problem is solved.

FIND OUT MORE

“Seven years ago our Detroit Series 60 developed blowby. Instead of rebuilding, we simply used FTC Decarbonizer and Flushing Oil Concentrate to clean up the internals and fix the problem. We continue to use Cost Effective Maintenance’s products, and the engine has now clicked over 1.5 million km and is in great condition.”

— Riseley’s Bulk Haulage

With age, engines normally accumulate some sludge and a bit of carbon around the piston ring grooves and elsewhere. A mix of operating conditions, quality of maintenance, and how quickly the lube oil blackens can all increase deposits and tip an engine into blowby territory.

Truck Blowby Can Be Reduced or Avoided

“Our Cummins-powered Kenworth T650 suddenly lost power and started smoking so badly that it was black-banned from a mine site where we had 18 months of contract remaining. After speaking with Brid at CEM, we used FTC Decarbonizer and Flushing Oil Concentrate and avoided a $32,000 rebuild.”

— Maslin Bros Earthmoving

The important thing to remember is that blowby is a serious problem — it generally won’t correct itself and can only get worse. If it is caused by wear, ignoring it risks more serious damage or failure, and much higher costs to rectify.

Before You Authorise a Rebuild

A rebuild is a big spend, so it’s worth working through a few low-cost steps first to find out whether you actually need one:

  1. Get a baseline test. Have a compression or cylinder leak-down test done and note the readings, so you have something to compare against afterwards.
  2. Clean up the internals first. Run FTC Decarbonizer in the fuel and do an oil change with Flushing Oil Concentrate to dissolve the carbon and free any stuck rings.
  3. Re-test and compare. If compression has recovered and the blowby has eased, the cause was deposits — not wear — and you’ve just avoided a rebuild.
  4. Only then decide. If the readings haven’t improved after a proper clean-up, you can authorise the rebuild knowing it’s genuinely needed — not as a guess.

This way you spend a few hundred dollars to know, rather than thousands on a rebuild that may not have been necessary.

Our best advice: clean up the internals first and determine for sure whether it really needs a rebuild. In over 80% of cases, that’s all you’ll need to do.

Want the detail? See the full method and four real truck case studies in our guide on engine blowby problems — most don’t need a rebuild, or the step-by-step how to fix engine blow-by.

For more information on fixing truck blowby, give Jimmy and the team at Cost Effective Maintenance a call on 07 3376 6188.

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