Okay did a couple of quick searches and couldn't find anything really. Anyhow, when checking the motor oil level, is it best to check it when the engine has been sitting cold or is it best to check it when it's already hot? I ask because everybody has a different answer, but I want something more conclusive. Thank you in advance.

 

Engine definitely warmed up.

 

I always check oil level with the engine cold.

 

I've always checked mine when motor is cold.

 

As far as I know ideally it should be checked it with the engine cold so all the oil can be drained into the pan. At least thats what is recommended for piston engines. I don't think it really matters though...lol. Probably a 0.1 quart of a difference if that.

For draining oil the engine should be warm.

 

Awesome, thanks guys.

 

Too bad there isn't a FAQ on this forum with a link to a free scanned online service manual so you could check and see if 3 out of 4 respondents to this thread gave you the wrong answer.

 

Yeah, always warm is the best way. Owner's manual even says to wait five minutes, which is why you check at every gas fill up after you've pumped your fuel. I don't see a need in waiting more than a minute, but that's what the manual says.

 

I've never seen a difference between a "cold" level and warming up then waiting five minutes...so I don't consider my answer to be wrong.
Maybe it makes a difference on a turbo engine but not on a NA.

 

Actually i tested today. I checked my oil level before i went for a drive (first start up of the day) and went for about 30 mins ride. Parked it and waited for 5 mins and check my oil level again.
It seems to be the same, but i am not running omp (just premix). Engine is an 88 AE.

 

Oil expands when hot and contracts when cold. The difference between a hot and cold reading depends on the temperature difference and the dimensions of the oil pan. You will not see any significant difference on an RX-7 if you live in a warm environment. Those who live in a cold environment will probably see a 1/2 qt difference. The main reason for checking the oil when warm is to avoid over-filling the engine. You can check it cold to make sure it is at or above the minimum level, but don't top it off to Full when cold.

 

Makes sense, thanks for the thorough answers. Eventhough I neglected to check the FSM (I frankly didnt think the answer would be there), I appreciate the insight from everyone, specially Evil Aviator.

 

Do I win a bag of popcorn? Make mine caramel, please.

 

 

True, but an insignificant amount.
According to this chart, unused motor oil expands .00039% for every degree Farenheit, so assuming an ambient temp of 75° and a running temp of 180°, the volume of oil has expanded .04095%.
Our cars take roughly 5 quarts of oil, which is 160 fluid ounces, so it would expand by @6.5 ozs.

There must be another reason for Mazda's suggested method because expansion of the oil volume is trivial.

 

It doesnt matter when you check it, its the same either way.

 

i check mine in the morning

 

Nearly 1/4 qt does begin to become significant, and that would increase to over 1/3 qt in colder climates. However, it is not as significant as it would be in other engines, and you are probably correct in assuming that the Mazda engineers had additional reasons for specifying a warm check. Sometimes the sump dimensions make a difference (like a thermometer structure that shows a large scale fluid expansion reading for a small change in temperature due to the bulb/shaft design), but I don't think that is a factor with the 13B. I have worked with other equipment that specifies a warm or cold check based on the sump type or check valves in the oil system, but lacking any detailed explanation from Mazda I just follow the guidance in their manuals.

 

Yeah, I dunno.
We don't have windage to worry about and I wonder how much tradition is involved, opposed to real engineering logic.

 

Check oil when warm.

Always

I dont care what that on paper graph saids. in my experience, 4 qts of cold oil, when warm, gives me about 4.2-4.4 quarts of reading.

Dont believe me? try it on your car :P

Even Mazda's Rx-8 video ask you to check the oil when its warm.

 

I already have and see nowhere near the difference you do.

 

hmm ... I dunno then

cuz mine shows the difference :P

maybe u got a special dip stick? haha

 

Thank you for making me smile today. It's also too bad there isn't a FAQ with a link to a free scanned online fsm for 80% of the posts on this forum. But sometimes you have to spell it out.

Always check your oil level with the engine fully warmed up, and the engine off for at least a few minutes.