I recently rebuilt my ZC because of a broken ringland. I now have 1500 miles on it. I had the block bored and honed. It has, new oversized pistons and rings, a new factory Honda oil pump, new oil orafice in the block, new ACL bearings, and new honda gaskets and o-rings. The crank was micro polished. The bearings were all close to the middle of the specs for the rods and mains. The oil pressure is around 85-90 psi at start up and at idle, when warm, it is 15-20, both readings are normal. Here is where it gets weird. The other day I was driving and noticed that the oil pressure was around 40psi when driving on the highway, at around 3300 rpms. Normally, for my car it is around 50psi at this rpm. The only thing I have done recently was change the oil and filter. Oil level is good and no leaks. I used 10w40 valvoline with a Hamp filter. This is the first time I have used a Hamp filter, I usually use a Napa Gold, but thought I would try the hamp. When I pulled over the idle pressure was normal @17psi. I revved the engine a couple of times and the pressure climbed back up to around 60+ psi.

The next day I started it and everything was just like before for the pressures. I dont think this drop in pressure, while driving is normal, or is it? I have never seen this drop in pressure before, even before the rebuild. There are no knocks or weird sounds, either. Any ideas? Do you think it could be the filter? I just bought 10 of them from JHP, for my Civic and my NEW Pilot . Or am I worried about nothing


Modified by Gorm at 6:45 PM 6/27/2008


Modified by Gorm at 6:47 PM 6/27/2008

 

Was it hot outside when this happened?

 

yes, about 90-95 degrees outside. My engine temp was 185. Thats why I use 10w40 during the summer, because it gets hot here, sometimes weeks in the high 90's to low 100 range.

Gary

 

I noticed the same thing last week when it was 95-102 degrees here. I lost about 14psi of oil pressure at ~3k RPM(~50psi instead of 64-70+) and about 7psi at idle(10-14psi instead of ~21). I got paranoid because I had knocked a small piece of RTV that had been sealing my valvecover gasket into the oil gallery that runs back down into the pan and thought it might be clogging the pickup and decided to drop the pan and take a look. While I did find the piece of RTV(and some other junk that had probably been there for a while) in the strainer, it didn't seem to be causing much blockage if any. I did notice that my oil looked kinda reddish grey as it was draining(I had changed my headgasket and valve seals the week before and used a lot of red assembly lube and grey ARP moly lube on my headstuds), so I just cleaned out my pan and pickup and put everything back together with fresh oil and new filter. My oil pressure seemed mostly the same, but this week when the weather cooled down about 20-25 degrees, my oil pressure is back to normal. My guess is the combination of assembly lube in my oil and the hot weather probably thinned it out(this was the first time I'd ever seen my oil temp go higher than my coolant temp) to the point where my oil pressure was affected. I use HAMP filters as well, and the one that was on when my oil pressure dropped had been on there through several oil changes(I had to drain my oil several times in the last month or so to do random stuff like resealing my oil temp probe, etc, with very little actual mileage on the filter), so it may or may not have been clogged. The oils I used in the last couple months were 10w40 and 10w30 Castrol Syntec Blend and 5W40 Rotella T Synthetic. Anyway, I would just continue to keep an eye on your oil pressure, especially in hot weather, and see if it changes. You can try a different oil and filter if you want to, but the HAMP filter is supposed to raise oil pressure, so you may or may not see an improvement with a different filter. 10w40 should be good for the summer, but you could maybe try different brands of oil if they're on sale for cheap in your area.