Topic: Oil pressure and temp

[Paul Lowe]

Have just completed a rebuild and everything seemed fine.

CB750 K1. Only got 100km since rebuild. When cold pulls hard runs well and oil pressure at 60-70psi (gauge). After a while oil pressure drops to 20-40 city traffic and oil light comes on. Bike starting to run rough but not too bad. Measured oils temp in tank after about 10mins and got 97 deg C.

Questions:
what is normal oil pressure range?
What is normal oil temp range when hot!
Will oil get thinner when hot and reduce oil pressure?
Is this temp just symptomatic of tight engine?

[PeWe]

Are all important O-rings replaced?
The o-rings on oilpump and the oil transportation from pump all the way to head?
There is a thread about important forgotten o-rings that can be replaced with engine in frame. http://forums.sohc4.net/index.php?topic=78643.0

Which oil? Maybe too thin? Motorcycle oil 20W-50?

Should no be temp. I ran my engine hot last summer, up to 110*C without any oil pressure lamp on idle

[Whaleman]

20-40 when hot is good. You must have a gauge. The light should not come on when gauge is 20 psi. Either gauge or sender is defective. I have a sump temp gauge. You have 206 deg F while I have seen 250 deg F many times. Dan

[70CB750]

What oil do you use?

But Whaleman is right, 20 - 40 hot is excellent and the 60-70 at cold is what i get too.  The oil light sensor is at around 7psi.

I run 20W-50 in summer and after long run - like 500 miles - the light would come on at idle, but thats an extreme.

[Paul Lowe]

I believe I did all the o rings. Oil 10W-40. Over pressure sensor original gauge brand new.   Both gauge and sensor in oil gallery.
Have checked under rapper covers and there was plenty oil on start up.

[70CB750]

Well isnt it summer where you are?  20w50 is better for the engine in hot weather.

[Bodi]

As mentioned, the oil pressure switch is basically a "whoa stop engine now!!" indicator that oil pressure is near zero. It should turn off below 10psi, on at maybe 5psi. If it's on with 20psi measured, you need a new switch as it may really fail and start leaking soon.

[bytio]

Honda manual shows 49 psi, at 60deg C  (oil temp) and 3000 rpm

[Paul Lowe]

Thanks guys. Maybe a new pressure switch is the go. Does it have to be Honda as they seem expensive? 4into1 have an after market for US$15.75 which seems OK.

Any other suggestions?

[70CB750]

Heavier oil. 10W40 is not heavy enough for your summer,  maybe in winter and still your engine would be happier with 15W40.

For summer 20W50 and your engine will last longer.

[chewbacca5000]

Are all important O-rings replaced?
The o-rings on oilpump and the oil transportation from pump all the way to head?
There is a thread about important forgotten o-rings that can be replaced with engine in frame. http://forums.sohc4.net/index.php?topic=78643.0

Which oil? Maybe too thin? Motorcycle oil 20W-50?

Should no be temp. I ran my engine hot last summer, up to 110*C without any oil pressure lamp on idle

+1  Had same problem as you and above thread fixed it.  O-ring and drill hub

[toolguy]

inexpensive replacement oil pressure switch on EBay.  exact size replacement  and
 fits under the cover properly  $6.25 and free shipping. From Honda Accord
Made by Original Eng Mgmt,  part# 8008

http://www.ebay.com/itm/Engine-Oil-Pressure-Switch-Original-Eng-Mgmt-8008-/301509845078?vxp=mtr

[Duke McDukiedook]

Yeah, you should be able to replace your oil sensor with a CIVIC or Accord sensor.
Just take it into your local auto parts store and match it up.
 

[chewbacca5000]

I re-read your post and did some Google and what I found is that with modern oil coolers with a temp switch they are set to go off at 212F.  So running at 250F is way too hot IMO.  Doing the shift mod will increase oil pressure, shifting, and maybe even cooling.  An oil cooler could not hurt either.

Questions:
what is normal oil pressure range?
Should be 20 PSI at idle and 60 PSI running

What is normal oil temp range when hot!
It is good to have temp be less than 212F

Will oil get thinner when hot and reduce oil pressure?
Yes

Is this temp just symptomatic of tight engine?
Not necessary.

Also eliminating the factory casting flash around the cylinders and head greatly increase cooling as does adding an oil cooler.