Does one change the oil in an oil cooler?

[Captain Snooze]

I would like people's opinion on changing the oil when an oil cooler is fitted. I have done a little bit of Googling but I haven't read anything that is definitive. I agree with a couple of contrary opinions.
I have read that
1/ The hose couplings on a cooler are not designed for many cycles of remove/replace. (That makes sense)
2/ If one does drain the oil from the cooler it means the engine will start with out oil as the air in the cooler is replaced by oil unless one fills the oil cooler first. (This makes sense too)
3/ If one does not drain the oil from the cooler then when an oil change is carried out the new oil is immediately contaminated by the remaining old oil in the cooler.( Yep, that rings true).
4/ That the amount of dirty oil is negligible compared to the total volume of new oil. ( I would prefer 100% fresh oil, not 90% new oil).

People's thoughts on the matter would be appreciated.

[Josh B]

You can never get all of the old oil out of an engine anyway, so IMO, the contamination bit wouldn't apply. Depending on how much the cooler adds in capacity, my guess would be 1/4 of a quart or so, I wouldn't worry about it. I have had a car with an external oil cooler and I never drained that when doing an oil change.

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[s2kdrew]

Same as all turbo car, kept a lot of oil at turbo. The oil turns all dark as soon as you start up the engine.

[Coheed]

Its negligible. No worries.

[arghx7]

Only if you've pulled the engine out of the car. Otherwise, drain and refill oil as normal.

[FT-86 SpeedFactory]

Originally Posted by Coheed

Its negligible. No worries.

^ This.

Evo's and more we change oil as normal. No issues and standard procedure.

[gmookher]

Originally Posted by Coheed

Its negligible. No worries.

x2

[Draco-REX]

Also, #2 isn't an issue since, when the oil is cold like at start up, the oil isn't being diverted to the cooler. The oil will follow the stock pathway.

[Shiny]

As stated above. The quantity is small so no meager issue here to oil quality.
Unless the oil in your engine is contaminated (Oil Water mix …) then a flush before the oil change is required.
Or you have a huge heat exchanger (unlikely on road cars) J .
Don’t worry about it.

[empower-auto]

My HKS cooler adds like 1qt or more. That's a fair amount. I just stick to a low change interval.

[stugray]

My rules:

NEVER reuse an oil cooler from an engine that detonated.
They are relatively cheap, just replace it.

For oil changes, I built a tool that allows you to flush an oil cooler with new oil before hooking it back up.



My racecar external cooler(s) hold over 3 quarts.....

[Shady195]

Originally Posted by stugray

My rules:

NEVER reuse an oil cooler from an engine that detonated.
They are relatively cheap, just replace it.

For oil changes, I built a tool that allows you to flush an oil cooler with new oil before hooking it back up.



My racecar external cooler(s) hold over 3 quarts.....

The NSA is gonna love that picture.

[Tor]

Originally Posted by stugray

For oil changes, I built a tool that allows you to flush an oil cooler with new oil before hooking it back up.

Cool tool! How does it work?

[justatroll]

Originally Posted by Tor

Cool tool! How does it work?

You fill the "pressure vessel" (c o o ker) with new oil and hook it to the cooler line.
Then pressurize with air to about 20 PSI & open the ball valve.

It will push new oil into the cooler and push the old out.

It is a little more important for my racecar because I have >20 feet of 12 AN hose and two coolers on a mid engine for about 3-4 extra quarts on a 5 quart engine.