PDA

View Full Version : Oil pressure on 7.4L Vovlo



AZ_Eagle
05-29-2001, 08:03 PM
I'm sorry if this post is off base for this message board, but I can't seem to find an answer to this problem, so I'm going to ask anyway. I am running a completely stock 1996 7.4L Volvo (carb) 310hp with 160 hours on her. You can run her all day on the primary's without a problem. Open her up over 4000rpm where the secondaries on the carb open and leave her like that for more than 5 minutes... the oil pressure starts to drop from 60lbs to 35lbs. Back off to where the secondaries close and the pressure slowly builds back up to 55 - 60lbs again. Anyone have a clue? I have checked the sending units mounting tube and it is clean as a whistle. I was considering putting an ATI Procharger on her to get some decent speed out of this rig, but I really would like to figure out this oil pressure issue first. This has been going on now for the last 15 engine hours. The engine behaves normally in every other aspect. Any help would be appreciated.
Thx,
Gene

moomba
05-30-2001, 03:56 AM
What are you using for oil weight? It almost sounds like you are using a multi-weight. It seems to be breaking down because of heat. Synthetic??

AZ_Eagle
05-30-2001, 06:23 AM
Originally posted by moomba:
What are you using for oil weight? It almost sounds like you are using a multi-weight. It seems to be breaking down because of heat. Synthetic??
Thanks for the reply moomba, I am using Castrol GTX 20w/50. The manual recommends 20w/50 or 30wt for running in the temperature range above 32F. All of the other recommendations are for colder temps. Are you recommending that I go with the 30wt instead?
Thx,
Gene
ps. I didn't request the frown icon... And I can't seem to get rid of it (Clicking the "Disable Smiles in This Post" does not work...
[This message has been edited by AZ_Eagle (edited May 30, 2001).]

dcraig
05-30-2001, 07:24 AM
The drop in oil pressure is most likely caused by an increase in oil temp due to harder engine load. This is somewhat typical (oil gets thinner with higher temps). Unless your stuck on synthetic oil, you might want to switch to a strait 40W if the rise in temp bothers you and see if that helps. Your other alternative is to install a larger oil cooler.

Racing Ray
05-30-2001, 08:44 AM
.
[This message has been edited by Racing Ray (edited March 12, 2002).]

ponponracing
05-30-2001, 08:45 AM
Full synthetic will help you keeping better oil pressure under load. Just make you use full synthetic oil, not blend or synthetic reinforced oil.
The tree main reasons for which you may loose your pressure are:
-Not enough oil in pan
-Some clearances are too wide inside
motor. Synthetic oil will help,
higher oil grade will also help, but
don't go higher than a straight 30
grade. Remember we talk about a
stock low hp motor.
-Oil temp. getting too high. First,
make sure the cooler is not clogged
by debris or grass, then you may
consider using a larger cooler.
You didn't mention about the water temp.. If this is a new problem, I would first have a look inside the cooler, then I would have a serious look at the water pump impeller. When you solve the problem, make sure
you mention the solution on this forum since I'm sure many boaters see the same problem with their rig.
A last point: before to add boost in your engine, make sure everything work fine.

ponponracing
05-30-2001, 08:50 AM
RacingRay has a point. Try a new filter, and why don't you go for an oil change at the same time. The solution can be that simple.

AZ_Eagle
05-30-2001, 11:05 AM
I'll try the oil filter first.... you might have something there, as the pressure issue also occurred about the same time I changed the Oil and filter. I'll let you know if this solves the problem.
Gene
Originally posted by ponponracing:
RacingRay has a point. Try a new filter, and why don't you go for an oil change at the same time. The solution can be that simple.

moomba
05-30-2001, 11:07 AM
hey ponponracing, why do say no to go higher than a 30w on marine engines??

ponponracing
05-30-2001, 02:30 PM
Moomba,
30 is a nice grade of oil for two reasons: it's liquid enough to give a good internal splash when cold and it stays tick enough to maintain oil pressure when the engine is hot.
The good thing with 40 oil is that it's stays ticker when it's hot. So it's excellent with an engine with wide clearances on the crankshaft. The problem with straight 40 oil is that it is too tick when it's cold. It doesn't lubricate properly because it doesn't flow enough and since it is too tick, the oil thrown from the crank will hardly lubricate cylinders, meaning pistons scuffing.
Instead of straight 40, I recommend that you use 25-40. It's a 25 grade that act as a 40 when hot.
If you want absolutly to use a 40 grade, do as we do in racing: preheat the oil before cranking up. Interested?

jet496
05-30-2001, 08:40 PM
I have a new 21 foot Ultra Boat Stealth with a 496 HO, AA impeller with a pre-loader impeller. Runs 61 mph at a hair over 4800 rpm's (AA impeller keeps rpm's down). I love it! Pulls my 200+ lb a-- right out of the water with out any resistance. My question is Marine Power specifies on the motor to use 40 w oil. The motor maintains a steady 150 degrees all day long. Should I stick with 40 w or go to 30w or 25-40w? I'm assuming since this is a high output motor it needs the 40w. What do you think. Also considering a procharger one of these days. Would want more internal specs. on the motor before doing.

ponponracing
05-31-2001, 04:01 AM
What do you mean by a high output motor? If your engine is hot, go 25w50, or better full synthetic 5w50 or 10w60.
400hp is not hot.

moomba
05-31-2001, 04:40 AM
Is there any advantage to a diesel rated motor oil? I have been told it is better for marine v-8's. It is supposed to handle the stress better. I just swithed from Valvoline 30 to Chevron delo 400 sae 30. Will this do any harm?
[This message has been edited by moomba (edited May 31, 2001).]

jet496
05-31-2001, 05:59 AM
There's a staight 496 & then there's a 496 HO (High output). I don't know what they mean by the High Output. Never said the motor was hot (actually is 460 hp on the dyno). Motor does not run hot either(150 degrees). Question was should I use 40w oil as Marine Power specifies or use a 30 w or different w oil as people are saying above.

MaddMan
06-10-2001, 10:44 PM
A couple things to remember about engine oil...viscosity improvers, that are excessive in 10W30 and 10W40 oils, break down at high temperatures...Quicksilver has a 25W40 oil that has no viscosity improvers, so it works great in marine use. Synthetic oils are not a wise choice in an engine that sits for any period of time without running (ie. boats) because they dont leave a film of oil on the internal components of the engine when they run back into the oil pan...petroleum based oils leave a film of oil when they drain...if you run your boat every 3 or 4 days, synthetics may be OK...but if it sits for a week or more between crankings, you might want to stick to petroleum based.
Dave
(p.s.-oil is cheap, rebuilds arent...try some different types in your engine and you'll probably find one it likes)

jet496
06-12-2001, 08:35 PM
Thanks for the reply MaddMan. So do you think I should keep using 40 w per Marine Power in my 496 HO. I used 10-30w in my 390 hp 454. Probably not a big deal since I'm not really really pushing the limits, especially since I have a AA impeller which keeps me at 60 mph at only 4800 rpm. I've always used Penzoil. Heard it's not a good oil, leaves ash in the motor. I never saw or had any problems with it though. I've always used it & never had oil related engine problems in my life. Sounds like I should stay away from synthetic. Makes sense if it doesn't leave a coating (Excellent input).

dcraig
06-13-2001, 08:12 AM
From my understanding of Synthetic Oil, it makes a molecular bond between metal engine parts. Regular oil does not.

jet496
06-13-2001, 08:40 PM
So the molecular bond with synthetic is the same as leaving a film coating with regular oil?

dcraig
06-14-2001, 08:26 AM
When I spoke with my engine builder, he said the syn oil bonds to the engine parts. Regular oil does not.
I change my oil every 30-40 hours anyway and run my boat about every other weekend.
One way around all this if your concerned is to install a prelube system. It runs oil throughout the engine before you fire it up.
What I do when the boat has not been run for a while is to disconnect the coil and crank it until I see some oil pressure on my gauge.