View Full Version : Oil Pressure Dropping

Tony B
11-20-2016, 05:53 PM
I have twin Crusader 270 engines - 350 Chevy Block.

Heading down from Knoxville, Tn. area I noticed my stbd engine which normally held Oil Pressure at about 55 psi, started slowly losing pressure.
Recently. I had made a new dashboard with all instruments and on short play trips of about 3 or 4 hours i noticed that it was getting lower. We were giving the engines a good run the other day because we are planning to head further south. My starting oil pressure is the old 55 -60 PSI. After about an hour or so it dropped down to about 50 and then to about 45. In idle it dropped below 30.

I tried to find a reliable mechanic but they are hard to come by. One was supposed to come by today but never called or showed.

Until he finally gets here, I am in a panic. My oil seems clean, there is hardly any smoke, I'm not using any oil and the engine seems relatively quiet and runs smooth.

Anyone have any idea what this could be?
I'm in panic mode, not just because of the expense of repairs, but also, If we dont leave soon we will probably have to stay till spring.

Thanks in advance

11-20-2016, 06:27 PM
You have 2 oil pressure gauges? If so, try swapping the leads and see if it is the gauge (fingers crossed). If the gauge checks good, there may be a sensor going bad. I say that about the sensor if it is not a mechanical gauge. I would also say the 30psi oil pressure at IDLE isn't too bad. If it is dropping off at cruising RPM's, I would watch it closely along with the engine Temp gauge. If the Temp starts rising, immediate shutdown. Not knowing what kind/brand of HB you are on, I can't say anything as far as being able to change out the oil pump without a lot of work. My Grandparents boat, just enough space to drop the oil pan and get to the oil pump (been there done that). I hope it isn't the pump.

Tony B
11-20-2016, 07:56 PM
I dont have a HB. I have a 36' Mainship motoryacht. The boat and engines are about 30 years old. The gages and senders are new. When installed about 3 months ago, the new ones read the same as the old ones. The pressure on the stbd engine started dropping before the gage swap and is continuing to drop. At start-up the PSI is about 55 -60. After about 30 mins, the press starts to drop to about 45 or less. When in idle, the press drops below 30. The water temp remains at its normal 160 - 165.
I too hope it's not the pump because I dont know if the mechanic will be able to drop the oil pan as is.

11-21-2016, 02:12 AM
we have 454's with 400 hours,they run 40-45lbs at 2000 rpm and around 20 at idle on all gauges.

11-21-2016, 05:54 AM
I answered in the duplicate thread. What does the Crusader manual say the oil pressure should be? 30 PSI on a Chevy small block in a car at idle is good. What oil viscosity are you running? If you want to know the actual pressure, you will need to hook up a manual gauge.

Tony B
11-21-2016, 06:15 PM
MY concern is not with the actual number of PSI, but with the fact that it dropped so drastically recently.
I just bought a mechanical gauge from Advanced Auto. Either tomorrow or Wednesday I will try it out and see what happens.
Thanks for the replies and keep them coming.

11-21-2016, 07:53 PM
Check oil for metal

11-21-2016, 09:38 PM
Cut the oil filter check for metal. DON'T use a hacksaw

Tony B
11-22-2016, 09:29 AM
Curious questions:
1). I know metal in the oil is not good, but what would it tell me in this particular situation?
My exhaust is clean - virtually no smoke.
2). The sea water hose on the oil cooler was removed at the heater exchanger end and and the inside of the hose wall showed (actually felt with finger and then a long swab) showed no sign of oil in it.

11-22-2016, 06:10 PM
Metal in oil can indicate wear from bearings which increases clearances which reduces oil pressure. Probably time to have an oil analysis performed. if you do have a problem it can help identify the problem area.

Tony B
11-22-2016, 07:29 PM
Toay. I completely removed starboard (Problematic engine) oil sender and shut-off alarm and "T" and installed it in the port engine - the good engine. I was hoping I could nail this on the senders but not so. I ran the port engine for almost an hour tied to the dock at 16-1800 RPM which is about my normal cruising speed. The engine started at about 60 psi and went to about 53 PSI when I went to 1400 RPM. When I ran it up to and held 1800 rpm it steadied out at around 55 plus a tad PSI. The bad news is that the senders are fine.

Tomorrow, I will install the new mechanical oil press gauge in the starboard engine (Problematic one) and hope it works out fine. That will then narrow it down to an electrical problem.
If pressure really is low according to the mechanical gauge, I am probably in serious trouble.

So if the mechanical gauge shows low, I will try OHB's idea of breaking open the oil filter. God, I hope its not that.

Wish me luck.

Tony B
11-22-2016, 07:31 PM
Metal in oil can indicate wear from bearings which increases clearances which reduces oil pressure. Probably time to have an oil analysis performed.

OK, now i'm scared. If I have to have an oil analysis, exactly what do I have to do and where do I have to go?

Thanks in advance.

11-23-2016, 05:37 AM
I would not get all excited. The oiling system relies both on pressure and volume. I really would not expect 50+ PSI at 1,800 rpm. I know that is what you are used to, but as long as you have good volume, you should be good at 25 PSI at that rpm.

Tony B
11-23-2016, 07:09 AM
It's not the volume that I'm worried about. its the fact that this happened so quickly. One day I have 55 psi and the next day I have 40 psi. Will I have 20 PSI tomorrow in the middle of nowhere while on a 600 mile trip? I am planning on leaving my current location around Dec. 1.

11-23-2016, 09:57 AM
You could also have a bad spring in the relief valve in the pump, they will cause a sudden change in pressure. The first thing to do is open the oil filter and check for metal. It will cost you around $6.00 and tell you more then anything.

Tony B
11-24-2016, 12:17 PM
Yesterday, I installed a mechanical oil pressure gauge. Started the engine at 60 PSI, then slowly drifted down to 55. I ran the engine for an hour at the dock at 1800 RPM in reverse gear for a load. Guess what? Nothing happened, the engine just sat there steady at 55 PSI. Great news, I can now sleep better and plan my trip southward next week. I will leave the mechanical gauge in place and use it. Although I only drive from the fly bridge, I make engine room checks about every 45 mins to an hour and the alarm buzzer thingie is hooked up so I am not worried about a real live oil drop.

So now I know that the problem is not the "T", nor the alarm sender nor the pressure gauge sender. There are only two things left (Ithink), either the gauge is defective or there is some sort of wiring conflict. I will put the sender wire from the good engine (port) and put it on the suspect engine's (starboard) gauge and that will tell me if the gauge is defective.
Anyway, now I can sleep tonight.

Thanks for all the help. I really learned a lot.

11-24-2016, 03:33 PM
glad everything is ok, have a good trip

11-24-2016, 05:54 PM
Glad you found it, it was sounding expensive there for a while.

Tony B
11-25-2016, 05:43 AM
Thanks for all the help and encouragement. I was starting to panic.

Looks like I will be ready to head back to Tx next week.

12-02-2016, 01:13 PM
Crusader does not recommend mutible viscosity oils, try 30 winter and 40 summer. Glad you came by yesterday, good to see you.

Tony B
12-03-2016, 08:26 PM
Yes, it was great seeing you again Ed. Wis we could have stayed longer.
We went from your place to Demopolis Friday. that was 5 locks and 90 miles in one day - with a late start due to fog.
man, I am tired.

12-13-2016, 11:05 AM
I found it to be a bad sending unit on one instance