I had what seems to have been a small oil leak off my greddy turbo oil feed line. So after repairing everything I switched from 10w-40 to 5w-40. My wot pressure went from 80psi to 62psi while warm. Is this normal?

While doing the repair we still drained out a few quarts of oil, so I don't think there was oil starvation to cause any damage.

 

Going from a 10/40 to a 5/40 should not change your oil pressure when the oil is hot. At least not 18 lbs. like you have.

ROD

 

If by "a few quarts" you literally mean 3 quarts, then your oil level was dangerously low and there may be engine damage. The s2k takes 5 quarts or more to the full line.

 

We filled the empty bottles of the new oil with the old oil. We were able to fill up 4 and a half bottles. So I don't think I could have damaged anything while still having 4.5 qts in the motor. Let me know if I'm wrong.

HOWEVER... (Probably should have mentioned this before, was dead tired and couldn't think.)

I forgot a important piece to this puzzle. The reason why my oil was leaking because the fitting I was using cracked.(The fitting is located where the OEM oil pressure sensor used to be.) It may have cracked due to the weight of the T Fitting/Oil pressure sender/Oil feed line and constant vibrations, or over torque. So me and my friends thought of another way to prevent the fitting from cracking again. We decided to use a hose to relocate the T-Fitting. Since the hose makes the oil pressure sender further away from the motor, could this cause a different reading? My gauge shows a constant 62 psi while at WOT and cruising at highway speeds. I drew up a diagram just in case I'm confusing anyone.



Do you guys think this extra 10 inch hose would cause a different pressure reading than before?

 

Two problems here. #1 Just because the weight of the oil weight is 40 does not mean it was the same viscocity as another 40 weight oil. There can be several points difference in the two. #2 If you lost several quarts changing that drain line you are starving the engine of oil. I really hope you topped it back off after that. If not I doubt you even have oil showing on the dip stick.

The temp of the oil is the main factor in what pressure it will show on the guage. You CAN NOT tell the oil pressure unless you have a oil temp gauge. Unless you can watch the pressure and temp together your pressure guage is hardly better than a dummy light.

Edit: Ok, you posted more info while I was typing. The small length of hose will not cause that big of a difference.

 

We spotted the problem before the oil levels were dangerously low, it actually never became dangerously low. While repairing the problem we drained all the old oil. We filled the old oil into empty 1 qt bottles. We were able to fill up 4 and a half bottles there for I don't believe there was any starvation.

I put in Castrol Edge 5w-40, while previously it had Amsoil 10w-40. I did notice that the Castrol was not as thick as the Amsoil while being poured in.

 

Thats the issue right there. Theres no way those two oils have the same viscosity values. Combined with the temperature issue it would be very easy for the pressure to change that much.

For example: On my other car I could have anywhere between 15psi of oil pressure at 300F, 35psi at 210F, or 60psi at 120F. Thats with the same brand 10w-30 in it too. The coolant temp never varied more than 20 degrees either. If you have the gauges side by side you'll be surprised at how the oil temp can vary depending on different driving conditions. I could even see a difference on a hot summer day cruising on the interstate and going into a rain storm for an extended time. The road spray had enough cooling effect on the engine/oil pan to see a temp drop and the pressure raised a small amount.

 

Thats the issue right there. Theres no way those two oils have the same viscosity values. Combined with the temperature issue it would be very easy for the pressure to change that much.

For example: On my other car I could have anywhere between 15psi of oil pressure at 300F, 35psi at 210F, or 60psi at 120F. Thats with the same brand 10w-30 in it too. The coolant temp never varied more than 20 degrees either. If you have the gauges side by side you'll be surprised at how the oil temp can vary depending on different driving conditions. I could even see a difference on a hot summer day cruising on the interstate and going into a rain storm for an extended time. The road spray had enough cooling effect on the engine/oil pan to see a temp drop and the pressure raised a small amount.
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If this is the case then does that mean the factory oil pressure specs given by the service manuals only be accurate if you use OEM oil? Supposedly normal numbers are supposed to be close to 80psi.

 

Curiosity got the best of me. Check out the differences in the Amsoil and Castrol.

 

Not necessarily. As long as the weight is within factory spec and its at the same temperature then it should be close enough to compare with the factory pressure.

Just keep an eye on the pressure in the coming weeks and if nothing else changes then you don't need to worry. If it was fine before then just changing a fitting has most likely not caused some catastrophic engine problem.