HOT THIN OIL

QUESTION: My question relates to the oil pressure on my engine. I have a 1987 454 Magnum that when cold runs with an oil pressure of 60 psi. When the engine gets up to temperature, the oil pressure drops to 20 psi at idle rpm. Is this normal?

If I rev the engine, the oil pressure goes to 40 psi. It is the 20 psi at idle speeds that has me scared.

ANSWER: Your oil pressure readings are within specifications according to Mercury Marine. I agree that 20 psi is a little low at idle. The unwritten minimum oil pressure rule of thumb for high-performance big-block Chevys is 10 psi per 1,000 rpm. But it is pretty common for a stock motor to be less.

The reason that your pressure is dropping is because your oil is getting thinner when it is hot. I think you should first make sure that your oil is getting properly routed to the oil cooler. If your engine is equipped with an oil thermostat, make sure that it is functioning correctly.

If everything checks out, I suggest that you go to a higher-viscosity oil than you are currently using. In your warm climate, combined with warm Florida waters, you should be using oil with a little higher viscosity than someone in a cooler climate. I would either use straight-grade SAE40 oil or multiviscosity oil with the upper number of SAE50 such as a 20W50.

LOW OIL PRESSURE AT HIGH RPM

QUESTION: I was reading my performance-boat magazines and noticed your tech section in Powerboat. Your ads and articles are impressive. I wish I could do what you do for a living myself. I’ve built many engines and I’m having trouble with a rebuilt Generation IV big-block Chevy that is in my Checkmate this season. The engine was previously in a drag car. Maybe you have run into the problem that I am having at some point.

I have a 1972 Generation IV 454 that is bored .030" over. The engine is equipped with an M77 Moroso oil pump that has a welded and bracketed pickup. The oil pressure is 50 to 60 psi at idle speeds when the engine temperature is cold or hot. The oil pressure drops to around 10 to 20 psi when the rpm reaches 2,800 to 3,000 and above. If you bring the rpm back to idle, the oil pressure immediately goes back up to 50 to 60 psi using SAE 20W-50 or straight-grade SAE 40W oil.

In discussions I have had, a mention of insufficient pickup clearance to the bottom of the oil pan was made; consideration was given to a possible restriction in the oil cooler which is 22 inches long and connected with -12AN lines; not having a windage tray; crankshaft bearing clearances and so on.

There is 3/8-inch clearance between the bottom of the oil pump pickup and the pan. The crankshaft bearing clearances are at .0018" on the connecting rods and mains.

The folks at my machine shop suggested trying thin oil (5W-30) as a test to see if the situation would improve. It was felt that the engine could run on thin oil because of the tight bearing clearances. With the thinner oil, the oil pressure would stay around 30 to 40 psi when the engine was cold at 2,800 to 3,000 rpm, then drop to 10 to 20 psi when the engine is hot, running at 3,000 to 4,000 rpm. One rule I understand is that it is desirable to have 10 psi oil pressure for each 1,000 rpm with a big-block Chevy engine.

The remote oil cooling setup has been removed and the adaptor plate was reinstalled with a screw-on WIX and/or AC Delco filter to the block. This test resulted in no change or improvement. The distributor has been checked with grease in the end for proper clearance to the oil pump shaft. This clearance is not the problem. I replaced the oil pump and it did not resolve the issue.

This engine never had issues rolling down the track at 7,200 rpm and maintained 60 to 70 psi oil pressure all day without a windage tray setup. This block was pulled to inspect the crankshaft, which was fractured. During the rebuild, the only items changed were the crankshaft, oil pan and camshaft. The cam bearings have not been replaced. So far, there is no metal in the oil filters since break-in with 10 hours on the motor.

I ran this same oil pan before at 5,200 rpm all day long without oil pressure issues, but with a stock oil pump on a 330-horsepower big-block Chevy that had a small oil cooler. This pan has a baffle/dam setup with a 1/2- to 3/4-inch cut down the middle to allow oil transfer to the back chamber. There are 12 quarts of oil in the system.

I’m getting ready to add two “stack breathers” as I only have one Mopar breather in one valve cover. I’m reaching for suggestions at this point. The machine shop that turned the crank and conditioned the rods for me is also stumped at this time.

Good windage control is very important to keep a good supply of nonaerated oil available for your pump. Oil that is picked up by the windage created by the crankshaft is aerated, heated and not available where it needs to be at the oil pump pickup. Simply having a windage tray may not cut it. Automotive oil pans with OEM-style windage control are not sufficient for the steady-state, higher-rpm conditions seen with performance marine engines.

So, whether or not your problem is being completely caused by not having good windage control, it is part of the problem. Install a pan and windage tray system designed for marine use. Most car pans don’t cut it. You can lose up to 50 horsepower by not having good windage control in your crankcase. Double check the clearance between the bottom of the oil pump pickup and the pan. I would not want it closer than 3/8 inch.

For some reason, your engine is using up the oil faster than it can return it to the oil pan. The fact that the condition improves slightly with thinner oil is evidence of that because the thinner oil can run back to the pan faster. It is likely that there is excessive oil leaking internally. I would double check to make sure that all oil galley plugs are properly installed. It is possible that the cam bearings have too much clearance.

Check the clearance around the distributor housing where it passes through the block. It is important that the slot in the distributor housing is aligned with the lifter galley passage. If it is not, oil could be restricted to the lifters and an internal leak could exist. With the engine together, the proper depth can be ascertained by removing the distributor. Then take a piece of welding rod and bend a little 90-degree hook on it. With a flashlight, look into the hole where the distributor goes and you can see the lifter galley passages.

With the rod, hook it in the bottom and top of the galley passage and mark the rod where the distributor sits in the intake manifold. Then compare that distance with the oil passage slot in the distributor housing to the flange including the gasket. This test is easier done when building the engine while it is still on the stand by simply removing the rear galley plug and looking to see if the oil passage in the distributor is lined up with the oil galley.

Your crankshaft bearing clearances are on the tight side for a big-block Chevy performance marine engine. I like to see about .0025" to .0029" clearance on the rod bearings and .003" clearance on the main bearings. Usually, it is better to have a few tenths more clearance on the rear main bearing. If your previous crankshaft was a stock GM piece with stock oiling, and the new one that you installed is one that has the main journals cross drilled, this could be a source of your problem.

We have found that cross-drilled crankshafts use (leak) too much oil for the sustained high rpm operation with wet sump engines. The crankshaft oil galleys receive their oil during the time the oil galley is exposed to the slot in the upper main bearing. Stock oiling crankshafts have one oil galley exposed to the oil supply at all times.

Cross-drilled crankshafts have four openings in each main journal, which results in two crankshaft oil galleys being exposed to the oil supply at all times. The excessive oil escaping between the crankshaft and the bearings can end up in a ball suspended like a tornado around the crankshaft.

Some later-model aftermarket lifters may not be compatible with your earlier Generation IV block. Make sure that the lifter is sealing the oil passages in the lifter galley and there is not some sort of groove allowing oil to leak by. Lifter to lifter bore clearance should also be checked to make sure it is not excessive. This also would result in an internal oil leak.

As long as there is no flow restriction in the oil cooler or the hoses and fittings, this is not likely the problem. The brand of oil filter you are using has no bearing either. I recommend that you use a high-performance oil filter such as the FRAM HP1, HP4 or HP6.

AMSOIL DOMINATOR SYNTHETIC RACING OIL

QUESTION: I have a 1997 Formula 382 FAS3Tech with carbureted 500-horsepower engines that I purchased last year. I am unsure of the history of the boat and the engines as it was originally a repossessed boat. I also have no idea what oil was used in the engines before.

Last year I ran Valvoline 40W racing oil. I wanted to switch to synthetic oil this year (Castrol Syntec 20W-50) but was told that there was a problem running synthetic oil in the older HP500s affecting the performance of the roller lifters. I heard the problem was that the synthetic oil was not allowing the rollers to turn and flat spots were being worn in the rollers causing failure of the valvetrain. I also was told that there was a service bulletin put out on this from MerCruiser.

I had a friend of mine who owns a marina call MerCruiser directly and ask them about it. He was told they were unaware of any problem with synthetic oil and HP500s. I also was told that you had discussed this in your column a while back. What do you know about this?

ANSWER: You are right. There has been an ongoing debate about using synthetic engine oils in motors that have roller lifters. More specifically, the debate is about engines that are equipped with hydraulic roller lifters. In the past, we have seen instances where the rollers were developing flat spots from skidding.

The reason that it was a problem with hydraulic rollers as opposed to solid roller lifter applications is that the valve spring pressure is less on engines equipped with hydraulic roller lifters. Most solid roller lifter endurance marine motors have valve spring pressures that are more than 200 pounds on the seat, and as much as 650 pounds over the nose.

Typically, an HP500 has around 150 pounds of pressure on the seat and about 450 pounds of pressure or less over the nose. The greater spring pressures used on the solid roller lifter setups help to keep the lifter rollers in contact with the cam lobes, which keeps the rollers rolling instead of skidding.

Crane Cams (which is no longer in business) was the manufacturer of the roller lifters used in your 500-hp Mercury Racing engines. Because of the observance of flat spots developing on the rollers when synthetic oils were used in constant high-rpm marine applications, it was Crane Cams that recommended not to use synthetic oils in engines equipped with their lifters.

AMSOIL spent a couple of years developing and validating a full-synthetic oil that, in part, specifically addressed this lifter roller skidding problem. The result was the release of a product line known as Dominator Synthetic Racing Oil in 2008.

Team AMSOIL participated in the validation process using the product in my race boat’s Mercury Racing HP525EFI engines. (AMSOIL is my race team’s major sponsor.)

Oil was evaluated after every race to be sure there were no signs of engine wear. After an entire season, all lifters were still in perfect condition. At this time, the one full-synthetic oil that I am sure will work for you is AMSOIL Dominator Synthetic Racing Oil. For your engines, I would use the same as what we use in the Team AMSOIL offshore race boat, which is 15W-50 (code RD50).

LOW IDLE OIL PRESSURE

QUESTION: I have a 1987 MerCruiser 454 Magnum in my boat. When the engine is cold, it runs with 60 psi of oil. But when the engine gets up to temperature, the oil pressure goes down to 20 psi at idle speed. If I rev the engine, the pressure goes back up to 40 psi, but that 20 psi at idle speed when the engine is warm has me scared. Is this normal?

ANSWER: I believe that your oil pressure is close to the minimum it should be at idle when the engine is hot. I would prefer to see it a little higher, but I don’t think you should be alarmed.

Being that your boat is used mainly in a warm winter and a warmer summer climate, I would consider increasing the capacity of your oil cooler. I would also go to a little higher-viscosity oil. If your engine has a lot of hours on it, consider using a straight-grade SAE 40- or 50-weight oil.

—Need some guidance from Bob Teague, Powerboat's lead test driver and owner of Teague Custom Marine? To send him an email click here.

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