Possible upcoming TSB - Serpentine Belt Slap
Hey all, it's me again. Mods, please move to whereever this should be.
***I WILL UPLOAD A VIDEO WHEN I'M NOT ON WORK WIFI***
We have started seeing a rise in the number of Mitsubishi Mirages, 2018 and 2019, all models, AC equipped with an aggressive belt slap under moderate load. The most common way to diagnose is to place a CVT in reverse, crank the ebrake up and hold the throttle at roughly 1425-1475 rpm. Using a flashlight in the engine bay (unless you have a well lit shop), you will see a resonance begin in the belt between the top two pulleys. From inside the vehicle, the complaints you should be hearing will be "sounds like a motorcycle", "sounds like a weedwhacker", or "sounds floppy". Customers (or you) will notice this at light-moderate throttle, only under load. It is very intermittant but easily repeatable on a normal drive.
The conditions have set on at no less than 25,000 and no more than 39,000km so far, and there appears to be no difference in onset between our city drivers and our highway drivers.
This belt slap can cause early fatigue of all engine pulleys and does not present with noise or vibration until it gets pretty bad, so I suggest adding this as a service point for us as owners going forward (don't worry about it techs, it's a headache to deal with through mitsubishi right now hahaha and the repairs pay **** all). CVT owners have it easy, those with 5 speeds may need to be pretty decent with the clutch to test for this without burning it out... I suggest a mild incline (5-7% grade) for audio diag or being VERY quick on the clutch when parked with ebrake set to hold just below 1500rpm for a few seconds. Vary throttle and clutch input as the load is what causes the slap, NOT just the rpm. The only 5MT we've seen required moderate throttle moderate clutch drag.
Mitsubishi's solution so far has been to provide us with a one way clutch pack to replace a pulley or two, to even out the tension. This is not a belt fault... it's just bad harmonics.
I suspect this may be a Canadian or Martime exclusive problem due to temperatures, corrosion on pulleys, etc..., however I'll keep you all in the loop. Working on our 4th one today (Mitsubishi on this one has supplied a slightly thicker belt), and I suspect given tech supports interest in this, that a TSB may be released once we hammer out a more reliable repair. A few other area dealers have seen one or two, same years, similar mileage.
Not sure how many Mitsubishi employees are on here, but please open a tech case for every case of belt slap. Help me get a unified resolution...
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View my fuel log 2018 Mirage ES 1.2 manual: 43.5 mpg (US) ... 18.5 km/L ... 5.4 L/100 km ... 52.2 mpg (Imp)