olysan

I was working on my boat most of last summer so I only really got to run it hard once at the very end of the season. After a couple minutes at wot I pulled back to idle and noticed that the oil pressure went from ~60 psi to almost 0. After just a few seconds (10-20) I gave the engine a little gas and the pressure came back to normal. The engine is a 406 SBC. Last summer I added an oil cooler with the permacool stat, and replaced the oil pan. I'm using merc accesories from a 1989 350 mag, including the original oil pressure sender.

Could this be a sender problem, or is that wishful thinking?

olysan

It was a while ago so I don't remember exactly, but I think I pulled back on the throttle pretty quick, like maybe 5 seconds travel time, and the pressure was closer to 5 psi than 10.

Thanks for the reply.

BadDog

Had a similar incident some time ago.
http://www.offshoreonly.com/forums/s...threadid=33874

Never happened again. No explanasion was ever found. I have not used the anti drain back type oil filter since and never had it occur again.

Tim T.

olysan

Just a note the alarm didn't go off when this happened to me. I think it was just a normal lag.

Vinny P

Electric guages are inherently inaccurate. If you even suspect a problem, before going crazy thinking about what may be wrong in the motor, simply put a mechanical guage on the motor for testing. This will tell the real story. If the mechanical guage reads the same as the electric, then at least you know where you stand.

olysan

Thanks guys for the replies. I'm thinking it's just a normal lag in gauge response. I probably should have known this since I sell pressure transmitters for a living.

tomcat

I don't know exactly how you plumbed the cooler, but there is another possibility that you should investigate.

When you added the oil cooler you added a lot of restriction with lines, adaptors, fittings, (remote filter housing?) and the cooler itself. Most engines have an oil bypass around the filter pad on the block. This spring-loaded valve is set to open if the filter gets plugged. If you added the cooler by putting an adapter on the filter pad, or plumbing into an existing remote filter setup the extra back pressure from the cooler and lines can cause this bypass valve to open.

So at WOT a lot of the oil will bypass the cooler (and remote filter!) if the original bypass spring is not changed to a higher psi spring. Your oil gets hot and thin really quick and when you drop back to idle you have no pressure. After a few minutes on fast idle the oil cools down and the pressure comes back.

I had the very same symptoms in my 502s. I had to change the bypass springs from the stock 11 psi spring to the stronger 30 psi spring. I'm not an expert on small blocks so you need to ask around on this. Whatever you do, fix the problem. No cooling and no filtering at WOT is bad news.

olysan

The engine had a mercruiser remote filter setup before I added the cooler. I'll have to take a look at it but.... I think the oil comes out of the adapter on the filter pad, goes to the perma cool stat, then through the cooler (or not), on to the filter, and back to the engine. The remote filter system is stock merc from a 1989 350 mag, I think they use the same one in the 454. Is the bypass valve in the block or the remote filter housing?

tomcat

On my Gen VI big blocks the bypass is in the block, but you have to check yours. Because it had a Merc remote filter already it maybe has the stronger bypass spring.