Gradually falling oil pressure

[indigo]

Back of the Envelope

I think we can get a little better idea of Clark800's cooling situation with a simple thermodynamic analysis. Here goes my shot at it:

You can reasonably assume that an A4 running at 2000 RPM in neutral (I think that was the operating condition) is at most consuming .4 gph of Fuel. With gasoline rated at about 115,000 BTUs per gallon, the energy input is about 46,000 BTUs per hour.
If you do a simple energy balance on the engine, energy IN has to equal energy OUT. The tricky part is the energy out in that it takes the form of heat rejected to the cooling water, heat in the exhaust gases, heat rejected to the engine compartment, power actually generated, friction losses, and any output by the alternator.
By and large, most of the energy OUT will be in the cooling water, especially with the engine being in neutral. We know that there are 4 gallons per minute of water flowing through the engine and the exiting cooling water temperature is 84° F. I found out from Clark800 that the inlet water temperature in the San Francisco Bay area where he was operating is 65° F. The heat rejected to the cooling water is found by simply multiplying the mass flow rate of water, in pounds per hour, times the temperature increase or delta T. Doing that math yields heat rejection to the water of about 38000 BTUs per hour. That leaves about 8000 BTUs per hour for everything else which, given the operating conditions, seems perfectly reasonable.

What I am suggesting is that the cooling system is doing its job quite well and the real overheating problem is a matter of an erroneous temperature indication. Either there is a problem with the instrumentation itself or there is some blockage or cooling water flow stagnation in the area of the sensor causing the high temperature readings. Without pulling the head, you really cannot ascertain how clean the head is or how open or closed the oval shaped cooling passages on the manifold side of the block/head are. The openings closest to the flywheel are the ones that provide coolant flow across the temperature sensor. If they or their coolant source are totally occluded, no amount of acid flushing will help to provide any flow through those passages and the temperature indicated will continue to be too high.

Tom Stevens

[clark800]

Tom (and everyone else who was skeptical about the temperature gauge): I think you're right. The IR temperature readings on the sender were a bit unstable (possibly due to its reflective surface), but they seemed consistently lower than the gauge reading. For example, the IR reading was 99F while the gauge was reading 155F. After shutting down the engine I also tried a grill thermometer on the sender and got 136F as the gauge was reading 180F. At that point the IR thermometer read around 125-141F. I repeated the measurement a few minutes later to make sure it was in equilibrium and got the same results.

The attached pictures show the IR thermometer readings in Fahrenheit while the engine was running after 10 minutes in neutral at 2000RPM after a cold start. Not shown in the pictures are the temperatures for the aft side of the engine at 128F, reversing gear cover at 133F, reduction gear at 65F, and exhaust pipes at 507F.

So if the temperature issue was a red herring, maybe there's a chance that the oil pressure can be maintained if I use a smaller propeller. I'll try to find one.

[Dave Neptune]

Clark, why the 2 sensors? Neither one is in the water flow because of the "tee". I'd get rid of the tee and install one sensor with MINIMAL thread compound or tape they can insulate the fitting if threads do not make "contact", seen that a few times. If you want 2 gages add the other to the top of the t'stat housing.

Those temp shots say you are not even hot! Now to the oil pressure issue. I would try a straight 40 wt or a 20-50 diesel oil and see if they maintain better pressure once warm. When the OP drops shoot the pan for some oil temps.

Dave Neptune

[clark800]

Summary and Update

It's been a long time, but I'm finally getting back to this issue. I had a few other problems, including a failure of some patches that I had epoxied on my fuel tank with JB-Weld that led to gallons of gas in the bilge. I learned to never use JB-Weld with gasoline despite their claim that "When fully cured, J-B Weld is completely resistant to water, gasoline, and about every other petroleum product or automotive chemical."

https://www.jbweld.com/pages/faqs

https://www.youtube.com/watch?v=brAu1VTivxg

Summary so far:
* The engine is a newly rebuilt Atomic 4 with the 2:1 reduction gear installed. The mechanic configured it with no thermostat and the bypass hose is internally blocked. It is raw water cooled.
* The engine starts out with high oil pressure (60PSI), as indicated by both an electrical and a mechanical guage connected through a brass tee, but after running in gear for 15-20 minutes the oil pressure starts falling. Both gauges fall at roughly the same rate, although the numbers don't match well at lower PSIs.
* I tried two different mechanical guages, both gave similar results.
* I tried changing the oil to Shell Rotella 15W40 multi-weight oil, which had no effect.
* I tried installing the Indigo Oil Filter kit, which had no effect.
* The mechanic replaced the oil regulator valve, which had no effect.
* I pulled the engine out of the boat and sent it back to the mechanic, he re-checked everything and installed a new oil pump, which had no effect.
* The water temperature gauge was indicating high temperatures (170-180F).
* I flushed the engine with acid to ensure to clear out the cooling passages, which had no effect.
* An IR thermometer reading confirmed suspicions that the temperature gauge was incorrectly reading higher than the actual engine temperature.
* The boat was overpropped (17x12in vs. 16x11in as specified in owner's manual), which was causing the transmission to slip and overloading the engine.
* I tightened the transmission to prevent the slipping.

Updates:
* It turns out the Sierra 18-5898 temperature sender I was using is for dual station setups only (Amazon recommends this sender to go with my guage, and the Amazon title and description don't mention anything about dual stations).
* After installing the correct temperature sender, the temperature maxes out at 150F when running at 2000RPM.
* I also removed the tee before the temperature sender, which was there to support a high-temperature alarm.
* A Sierra representative confirmed that my oil pressure gauge and sender match properly.
* I installed a 16x9in Martec folding prop (which is underproped vs. the manufacturer recommendation of 16x10in for a Martec folding prop). This made the oil pressure drop quite a bit slower, but it still fell from 60PSI to about 25PSI after 1.5 hours in gear at 2000RPM.
* I loosened the stuffing box a bit, which made the shaft spin more in neutral, but didn't affect the oil pressure.
* I took the boat out and motored for 3 hours at 2000RPM, temperature stabilized at 150F and pressure stabilized at 10PSI on the electric gauge and around 20PSI on the mechanical gauge (although the difference between 10PSI and 20PSI is an 1/8 in...).
* The engine sounded like it was running very smoothly for the whole trip, although the exhaust fumes were really bad when going downwind; could that be due to running without a thermostat or is that just normal?

So I think we can conclude that the cooling system is working well and the propeller is not the main culprit. The mechanic did say his engines (with the bypass blocked) typically run at 135F, so even at 150F it may be slightly hotter than expected.

I think the only suggested cause that hasn't been directly ruled out is the bearing/journal clearances... The only thing is that this mechanic has rebuilt hundreds of Atomic 4s and a friend of mine says he's the best mechanic he knows, and the mechanic says he checked the clearances and even took the engine apart again to re-check everything.

Are there any other potential causes? Or maybe it's time to ask the mechanic for an exchange?

[joe_db]

I would be pretty tempted to ask for an exchange.
That said, a couple of things stick out.
1 - 2,000 RPM is max? A reduction gear A4 should be able to hit more like 3,000 RPM.
2 - Has anyone determined the OIL temperature yet? 150 degrees is a bit hot for raw water, but plenty of FWC A4s run hotter than that. We either have oil way too hot or bearing clearances way too large.

If you can get an exchange, I would.

[tenders]

This is a bit outside of my experience, but my observation would be that a rebuilt engine running at 150° with a bypassed thermostat and at 10-20psi warm oil pressure at cruising speed is sending two strong signals that it has simply not been rebuilt properly. Those are symptoms of an engine that needs rebuilding, not one that has been rebuilt. And 60psi at startup seems like the adjustments have been overset to compensate for the problem.

Other indications: no effect from change in oil weight, no effect from regulator valve replacement...actually this last one, if true, stymies me. The mechanic should be having a cow if his rebuild exhibits this symptom. Seems like a "him" problem, not a "you" problem.

Some other discussion on this topic:

http://www.moyermarineforum.com/forums/showthread.php?t=6646

On the JB Weld...what I see from your video is a lot of shiny metal that's been scratched but apparently not scuffed to a sufficient degree to get good tooth. Is it holding well to the tank? Doubt it. Stainless/Monel is probably a harder alloy than JB Weld was intended to grab onto. These aren't really conditions for success with epoxy products. I'd advise a gasketed plate held down with machine screws.

I can't conclude anything about the exhaust situation. If you're going downwind at the speed of the wind, you can't escape the transom exhaust; that's normal. If it's coming out of the engine room, that's a problem.

[joe_db]

This is a bit outside of my experience, but my observation would be that a rebuilt engine running at 150° with a bypassed thermostat and at 10-20psi warm oil pressure at cruising speed is sending two strong signals that it has simply not been rebuilt properly. Those are symptoms of an engine that needs rebuilding, not one that has been rebuilt. And 60psi at startup seems like the adjustments have been overset to compensate for the problem.

Other indications: no effect from change in oil weight, no effect from regulator valve replacement...actually this last one, if true, stymies me. The mechanic should be having a cow if his rebuild exhibits this symptom. Seems like a "him" problem, not a "you" problem.

Some other discussion on this topic:

http://www.moyermarineforum.com/forums/showthread.php?t=6646

On the JB Weld...what I see from your video is a lot of shiny metal that's been scratched but apparently not scuffed to a sufficient degree to get good tooth. Is it holding well to the tank? Doubt it. Stainless/Monel is probably a harder alloy than JB Weld was intended to grab onto. These aren't really conditions for success with epoxy products. I'd advise a gasketed plate held down with machine screws.

I can't conclude anything about the exhaust situation. If you're going downwind at the speed of the wind, you can't escape the transom exhaust; that's normal. If it's coming out of the engine room, that's a problem.

I think that is the issue!!!!!!!!

[Mark Millbauer]

When you first posted the problem I suggested loose bearing tolerances. Particularly cam bearings. I suspect many A4’s are rebuilt without adequately addressing the cam bearings. Most of the time it works out ok. This is because they wear at a lessor rate than rods and mains but they do wear. They are also more difficult to replace and realativey easy to damage and or misalign when replacing. The cam bearing and journals play a significant role in oil pressure. Did the mechanic ever confirm that the cam bearings were replaced?
I also still question the oil pump replacement as its intregal to the main bearing cap. Did he just switch the pump gears? If the pump is truly suspect, As far as I know, only Moyer can properly test and rebuild it.

I truly hope you are able to resolve this.

[Marty Levenson]

Connection to oil pressure gauge

I may have missed this being addressed in your thread, but I had a similar issue. I had used a high pressure (grease gun I think?) hose to connect my cockpit mounted mechanical oil pressure gauge to the rebuilt A4. As it heated up - after half an hour under load - the pressure dropped alarmingly. When I moved the gauge to the block the reading stayed steady. Switched over to a copper hose and problem resolved.

[Mark Millbauer]

I once had an A4 that increased oil pressure as it warmed up. I used 10W30. In fact, I had to set it at about 35 lbs at idle so it would not exceed 40-45 or so at cruising RPM's after it ran for an hour or so. I attested it to excellent bearing and oil pump clearances that tightened up as the parts got hot.

I had another A4 that was experiencing low oil pressure similar to yours. I pulled the motor, set it on the bench with the pan off and connected a homemade oil injection unit to one of the oil ports. I Injected a gallon of oil at 20lbs pressure. The result was shocking. I was surprised at the amount of oil that sprayed out of all the bearing journals. The motor was complete other than the pan. It seemed like More oil sprayed out of the cam bearings than either the rods or mains. It made a huge mess int he garage. The cam runs parallel to and closer to the oil galley than the main journals.

A friend of mine had a Chev 307 in a 26' Bayliner cruiser. He was a professional mechanic. When warm, it averaged 10 lbs oil pressure on straight 30 weight. That engine ran that way for the 10 years he had it. Never had an issue. And those engines run much faster than our little A4's.

Oil pressure is important but so too is an adequate supply volume of oil to the moving parts.

I feel your pain and hope you solve the issue but on the other hand, I wouldn't be surprised to find your bearings getting an adequate volume of oil. I would almost be more concerned with too much oil pressure.

In the mean time,l you might consider using a good 20W50 oil in it and take it easy until the the engine warms a bit.

[clark800]

Thanks for the feedback everyone! Looks like I'll have to talk to the mechanic about an exchange.

joe_db:
1. I can reach at least 3500RPM, but there is some resistance around 2000RPM where giving more throttle doesn't affect RPMs much, and then with enough throttle it jumps to about 2500RPMs, but at that point it's a lot noiser, so I chose 2000RPMs for cruising RPM.
2. I just took some temperature measurements that might help estimate the oil temperature. After a 35minute dock test, I was at 150F+ water temperature and 30/35PSI oil pressure. The brass tee before the oil pressure sender was about 150F, the oil pan was about 190F, and shooting down the oil fill tube was 210F.

tenders: I'm sure the J-B Weld failure wasn't due to a poor surface bond; it was very strong when I initiailly epoxied it. The ethanol in the gasoline degraded the epoxy until it became rubbery and failed. I spoke with a J-B Weld representative and they acknowledged that they were already aware of the fact that ethanol degrades their product, but they refuse to update their advertising to mention this critical fact. They also chose to not respond to my letter to them or my complaint filed through the BBB for false advertising which is why they now have an F rating: https://www.bbb.org/dallas/business-...gs-tx-90299519
I ended up having the tank welded (after draining, venting, filling with water and argon), which is the only generally accepted option for gasoline tanks (even gasketed bolted plates are not advised).

Mark: Yes, it looks like you're right. Thanks for the advice about running on low oil pressure too.

Marty Levenson: That's really interesting that you had the same symptom and found a solution. I'm using the tubing that came with the Equus oil pressure guage, which I think is nylon. I'd like to understand what was actually happening mechanically, do you have any explanation?

[joe_db]

All true...but I would not tolerate 10 PSI on a new out of the shop rebuild!

[Marty Levenson]

tubing

Well, if it came with the gauge it SHOULD be fine.....but I would attach the meter directly to the block to rule out that variable.

My problem was heat: as the oil got really hot the tube got softer and gave a false reading.

[romantic comedy]

Interesting about the JB weld.

I thought that epoxy was impervious to everything until recently.

I replaced the float on my gas tank sending unit. First I used cork and it sunk in 2 days. That made me crazy!!

Then I bought a plastic float that is a replacement for antique Fords. It fit on the shaft but I needed a way to hold it on. I put a ball of JB Weld on the end on the shaft to hold the float on.

Then I sat it in the tank with no bolts. It was in the tank for at least a month before I got back to it. I lifted it out and the JB Weld felt rubbery but not too soft.

Now I need to remove that and try another way to hold the float on.

Oh well, it is a boat!!

[edwardc]

...Now I need to remove that and try another way to hold the float on. ...

Could you get a die and thread the end of the rod? Then use a pair of nuts with a lockwasher between them to hold it on. I wouldn't trust a nyloc nut here because I don't know how they react to gas or ethanol.