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Checking oil level when hot...why ?

RoseFarmer wrote:
I just could not resist.
The oil check is specified for check when hot, because of the same reason to drain oil hot.
The oil cooler is thermostaticly contolled.So draining while hot allows for the cooler to also drain.
If you are changing oil cold you will not be draining fluid from cooler.
And of course after the machine has cooled and you intoduce fresh cold oil the cooler is not filled untill operated up to temp and thermostat opens again.
This also why after an oilchange, when the system gulps after the thermostat opens , the machine will show a oil pressure fault.
Here at the Farm we try to drain while hot, but not always possible, so if done cold we loosen cooler lines and drain.
Either way after an oil change, a test ride is required, and the fault is cleared.We have never seen a false oil pressure fault again!!!
Hope this helps explain. Of course the tech just :) when we fiqured out a test drive was also part of an oil change!!!
Click to expand...

This doesn't make sense to me. If you have run the bike, it is hot thus thermostat open. You park it and the oil should drain back to the pan. Can anyone provide a reason that this doesn't happen? I've changed on a cold engines and don't get a fault so long as I fill the oil filter before I install it. Also the oil level is correct and not overfull when I check after the change.
 
I would expect that the thermostatic valve is open when the bike is parked hot, allowing the oil to drain down from the cooler. The valve would then close after the bike cools so that upon next start the oil doesn't circulate through the cooler until the bike warms up. So....checking oil cold or hot shouldn't matter much beyond the slight expansion of the oil when hot?? Under what conditions would oil be "trapped" in the cooler loop when the bike is shut down? I know I haven't observed significantly temp-dependent engine oil levels in my bikes that have had oil cooling. And it sure is a pain to work on a hot engine.
Rob
 
John and Zipster....

Thats what was nagging at me....:lol: It seemed to be a contradiction but I thought I might not have had enough caffiene...:blush:

Eric B)
 
The same question has occured to me. The oil must stay hot enough for long enough for the oil in the oil cooler to drain back before closing. For oil to be denied to the cooler at cold start time makes some sense but not the other way around.

Graham
 
GrahamNZ wrote:
The same question has occured to me. The oil must stay hot enough for long enough for the oil in the oil cooler to drain back before closing. For oil to be denied to the cooler at cold start time makes some sense but not the other way around.

Graham
Click to expand...

I also work on BMWs. If you look at the ones with oil coolers and sight glasses, you usually can't see any oil in the sight glass when you stop. You have to wait 20 minutes or more for the oil to drain to the sump in order to determine the oil level. So if you drain immediately, you won't get all the oil out, you have to wait for the oil to drain from the coolers. Since so many models require the removal of body work (I hate getting burned), I change them cold as well. I also fill the oil filters before installing them.
 
John

Although I always change oil when it's hot, I let the bike stand with the drain plug and filter out for an hour or even overnight before completing the job. But then as a home mechanic I'm never in a hurry.

Like you I half fill the filter with oil before refitting it. Bikes with the filter side mounted always worry me because of that.

Graham
 
ok. my two pence worth.
The oil cooler is in the pressure circuit? Assuming this, then how does the oil drain back? To do so would require a vent in the top of the cooler to let air in. So it makes no difference to the contents of the cooler whether the oil is hot or cold.
Or is the oil cooler on a seperate circuit on the Norge/Breva with an open end, ie. one which allows the oil to drain back?
If this were the case then every time you stopped the bike the oil would indeed drain back, then when you set off again, and the thermostatic valve opens, you would have no oil pressure for a moment while the oil cooler fills again.
This clearly doesn't happen.
 
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