90Q oil pressure test

Post by **Q45tech** » Sat Nov 09, 2002 9:41 am

My 90 Q 234,000 miles Mobil 1 [since 60,000 miles 1995] factory oil filter with 463 miles on 10w30 oil and filter:In park from crank

1037 rpm 120F coolant temp 39 PSI start up 900 rpm 132F coolant temp 34 PSI 815 rpm 145F coolant temp 29 PSI 775 rpm 150F coolant temp 24 PSI 775 rpm 158F coolant temp 22 PSI 775 rpm 167F coolant temp 21 PSI 775 rpm 174F coolant temp 20 PSI 775 rpm 177F coolant temp 18 PSIAfter 10 minutes 16 PSIShift to drive AC on to raise coolant to 181F 650 rpm 181F coolant temp 14 PSI1750 rpm 177F coolant temp 45 PSI2000 rpm 177F coolant temp 60 PSI2500 rpm 177F coolant temp 65 PSI2600 rpm 177F coolant temp 65 PSI3000 rpm 177F coolant temp 68 PSI

Guess we can safely say the Q oil pressure exceeds or equals the minimum of 14 PSI warm idle and exceeds the 61 PSI minimum at 3,000 rpm specified in manual

Post by **Q45tech** » Sat Nov 09, 2002 9:41 am

Guess I was right to use 50/50 15w50 Mobil 1 with 10w30 for this past summer's warm conditions as this 12.5w40 combo probably gave me a few PSI more at hot idle.By the way the filters burst point is around 90 PSI.And the maximum the system is supposed to put out is 81 PSI.

I was unable to determine the opening point of the oil filter bypass valve but I have ordered a very large face pressure meter which should have the accuracy to determine this.

For sure you high mileage owners don't want to use anything thinner than Xw30 weight......well maybe petro based oil are not as thin as Mobil 1......really have to wait till next summer for very much more accurate idle pressure test.

Pretty amazing after all those miles that the bearing clearances are still within limits with this oil.

Post by **longrunQ** » Sat Nov 09, 2002 9:41 am

The place in town where I changed my oil only had 10w30 and 5w50. I went with the 5w50. Is this OK?

Post by **PalmerWMD** » Sat Nov 09, 2002 9:41 am

longrunQ wrote:The place in town where I changed my oil only had 10w30 and 5w50. I went with the 5w50. Is this OK?

No.

2 reasons:

A 5w-50 has too large a spread between the base viscosity and the running viscosity.This means a lot of VI's were used in this oils formulation.Too many VI's make the oil less stable, take the place of otehr important additives and create a greater varnish load.

Also a 50weight oil is simply too thick for a Q, even in a 5w-.(Outside of unusual circumstances, ie a very hi mile Q in hi summer at extended triple digit speeds)

For winter use a 0w-30, 5w-30, 10w-30 (depending on climate).Prefrably a full synthtic oil.In summer a 40 weight (ie 0/5/10/15w-40)(MOBIL1, redline, AMSOIL and such)

Fred...

PS: You didn't use Syntec did you?:nono

Post by **longrunQ** » Sat Nov 09, 2002 9:41 am

Darn, thats bad news.

Should I flush it immediately and go with 10w30?

Post by **PalmerWMD** » Sat Nov 09, 2002 9:41 am

There is no need for a flush, but if it was my car i would change the oil to a 10w-30 or 5w-30 soon (synthetic!)

Fred...

Post by **Q45tech** » Sat Nov 09, 2002 9:41 am

Every engine condition [mileage and wear] is different. Assumming that they all used the very narrow bearing tolerances specified in the manual, you would have to measure the oil pressure to determine the PERFECT viscosity for each brand of oil.

As oils accumulate miles the viscosity increases as the lighter fractions boil off.........real synthetics may only lose 5% whereas conventionals may lose 20% or more by volume.

The highest pressure is not really critical, it is the lowest pressure at the hottest idle, that you have to worry about!

Remember the oil sender on a Q turns on the light when the PSI drops below 3.0.............wish I could find one with a 12-14 psi rating..........really just as easy to install an accurate gauge.

Anyway from the test measurements we conclude that my engine probably has another 100,000 miles at least.

Post by **PalmerWMD** » Sat Nov 09, 2002 9:41 am

Q45tech wrote:Anyway from the test measurements we conclude that my engine probably has another 100,000 miles at least.

that's really cool

That would bring it up to 340,000 miles then.What's your compresion right now?Does it burn or leak any oil?

Fred...

Post by **Q45tech** » Sat Nov 09, 2002 9:41 am

Haven't checked compression since 180k about 3 years ago. No oil use since Mobil 1 and valve cover resealing and the 3rd front main seal and 3rd rear main. Guees I'll have the compression checked in 20k @260k...........but why bother if the power balance can be maintained at exactly 0 rpm variance since it wouldn't be cost effective to rebuild the rings or replace valve seat as I have a like new set of heads from a 120k 1993 engine in waiting......need to find a low mile 94-95 block to fit the heads........or just get a newer car in 2005.......15 years is probably long enough...M45 ought to be $20k by then

Post by **AZhitman** » Sat Nov 09, 2002 9:41 am

Q45tech wrote:.......or just get a newer car in 2005.......15 years is probably long enough...M45 ought to be $20k by then

That's my plan as well. I want the "graphite/silver" one.

Post by **PalmerWMD** » Sat Nov 09, 2002 9:41 am

Mine too, maybe 2004 tho...

Fred...

Post by **Q45tech** » Sat Nov 09, 2002 9:41 am

Viscosity cSt @ 100°C 10.50 [10w30]; 12.50 [Quaker high mileage 10w30]; you could call this a 12w3515.11 [10w40] ; 20.50 [15w50]

http://www.cam.org/~jacobie/equa2.htmht ... s90126.htm

http://www.urbanracer.com/tech/tech.html

Post by **Q45tech** » Sat Nov 09, 2002 9:41 am

Having at spec oil pressure primarily tells you how the crankshaft bearings are, not necessarily how the rod bearings are holding up.Generally rod bearings are the first to go. The problem is if you wait for the sound [rod knock] the crank is probably worn.

90Q oil pressure test

90Q oil pressure test

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