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Tuesday, July 14, 2020

Doug's Domain

Doug Vetter, ATP/CFI

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Saturday, August 30, 2008

First Coolant Flush DIY

If I chose to follow the two year interval for coolant flushes as recommended on the E36 when it first came out (since changed to three years), I was due for a coolant flush in June. Due to my schedule and my desire to determine the proper method to flush the coolant I delayed the process...until yesterday when I completed my first DIY coolant flush.

I realize that certain purists may take issue with the method I used. Let me explain. A few months back while I was researching this task I discovered that in order to remove the block drain plug I would have to remove one of the pre-catalyst oxygen sensors. This is due to the use of the M3 headers on the M52 engine in 96-99 coupes. Since unscrewing the oxygen sensor would require me to repeat the process as documented in my Oxygen Sensor DIY article, I decided that I'd look for alternative methods and seek my technician's advice.

It's clear to me now that the dealer technicians do not remove the oxygen sensor and thus do what I choose to call an "abridged coolant flush". Just as an automatic transmission fluid change unavoidably leaves a good 30% of the fluid behind in the torque converter (unless, of course, you use a machine to cycle in new fluid as the transmission is running), the abridged coolant flush leaves about 50% of the coolant behind in the block.

The "abridged" technique is not as bad as it seems for one simple reason: the proof is in the pudding. My dealer flushed only half the fluid every other year and I managed to get 125K out of my radiator and 165K on the original heater core (knock on wood, of course), and I should mention that I replaced the radiator not because electrolysis had damaged the metal core, but because the plastic necks were about to fail. Fortunately, I won't bother to subject you to the sleep aid that would be a lecture on asymptotes as they apply to coolant flushes. Just trust in the knowledge that replacing half the fluid every year or two achieves the goal and protects the system.

The total cost for a coolant flush at the dealer is $220, $25 of which is for parts. Thus, I managed to save $195 by doing this job myself. It's not a ton of money, but as usual it's better in my pocket than anyone else's. Viva la DIY!

Mileage: 165115, Parts $25, Labor saved $195