Gradually falling oil pressure

[Mark Millbauer]

Did your mechanic confirm that all the bearings, including the cam bearings, were correctly measured and replaced?
As stated previously Your issue is consistent with slightly worn cam bearings.
Also, the oil pump can't just be replaced on an A4 as it's also the main bearing cap. To replace the assembly would require line boring. So I'm curious as to what he replaced when he stated he replaced your oil pump. The pump gears are matched to the housing.

Don can have your pump tested and rebuilt. It's expensive and would do nothing if your bearings and journals are not up to specification.

I'm sorry you're having to go through this.

[clark800]

Thanks for the replies!

@joe_db
I don't have parts for testing the manifold pressure yet, but I didn't have any trouble getting to 3000RPM and the experts at the local propeller shop said the propeller probably wasn't a major issue if I can get to that RPM. I am thinking of testing with the propeller off to see what happens.

The engine is already running with no thermostat - the mechanic disabled it somehow to prevent salt water damage with higher temperatures.

Shell Rotella 15W40 was suggested above and I tried it and it had no effect.

@ndutton

The thermostat dome is still on the engine. I'm not sure exactly how he disabled it. I can ask next time I contact him. If the cooling system was disabled, would the engine hold at a temperature of 155F for an hour at 2000RPM in neutral?

@Mark

I haven't asked about the details yet. I'll contact the mechanic after testing without a propeller.

[ndutton]

The engine is already running with no thermostat - the mechanic disabled it somehow to prevent salt water damage with higher temperatures.

The thermostat dome is still on the engine. I'm not sure exactly how he disabled it. I can ask next time I contact him. If the cooling system was disabled, would the engine hold at a temperature of 155F for an hour at 2000RPM in neutral?

Entirely possible. There's very little load on the engine out of gear so it doesn't produce much heat.

In the first sentence quoted above we have conflicting information, the reason I asked for more accurate detail before. Ask the mechanic if the thermostat was physically removed or disabled (it can't be both). If the former, did he block the bypass? If the latter, exactly how was it disabled? If the thermostat was removed and the bypass was not blocked at the same time you do not have a functional cooling system.

The thermostat in our A4 does not function the same as grandpa's Chevy, it's way different. It can't be simply removed without modifying the cooling system too.

[clark800]

@ndutton: I think you might be on the right track with suspecting the cooling system, or at least something related to the temperature. Here's why I'm suspicious about the temperature:

1. The engine seems to run a lot hotter than it should given that the thermostat is disabled. I still don't know exactly how it is disabled, but if I clamp off the bypass hose it seems to have no effect on the water flow out the transom or the water temperature, so I believe the bypass is internally blocked to force all water through the block at all times.

2. The mechanic said he could never get the engine over 140F, even running it in gear (without load) at 2000RPM+, whereas I'm seeing 155F in neutral and 180F in gear at 2000RPM with load. Of course, the propeller is slightly larger than the specification, but I took it to 4000RPM in gear, so I have to doubt that the extra inch of pitch and diameter is causing a big problem. Plus the propeller can't explain the higher temperature in neutral.

3. The water temperature reaches ~170F prior to oil pressure issues arising, so the elevated temperature may be causing the oil pressure issue. For example, if there is some kind of cooling failure, some parts of the engine may be significantly hotter than the temperature sender. It seems less likely that the causality is reversed because the oil pressure decline does not seem to be associated with a further temperature increase.


But I'm having trouble figuring out what might be causing the elevated temperature.

I checked the flow rate and about 6 gallons/minute of water is flowing through the cooling system, so that looks good.

I clamped off the bypass hose and it had no noticeable effect on the water flow rate or water temperature, even when clamped from a cold start. Also, the temperature pattern is the same when clamped. So I think the water is flowing through the block.

I checked the exhaust backpressure and it fluctuated wildly between about 1PSI and 3PSI, with brief spikes down to 0PSI and up to 4.5PSI, with an average of what I would guess as 2.5PSI, though it was too erratic to read clearly. This is higher than the specification, so I tried disconnecting the exhaust system and initially the temperature dropped from 160F to 140F in about a minute in neutral, but then it climbed back up to 160F just as quickly when I shifted into gear, and then I had to abort due to carbon monoxide alarms.

This exhaust test is the most promising finding because it's the only time I've seen the temperature fall to 140F and also the exhaust is one of the few variables that differ between my setup and the mechanic's. Is it possible that elevated exhaust backpressure could cause overheating without affecting water flow rate?

[ndutton]

Clark, my comments address only operating temperature and do not attempt to connect it to oil pressure. The temperature may be completely unrelated but it still needs to be dealt with. A few observations from your last post:

• I'd still like to know if you have a thermostat installed or if it was removed, same question I've been asking for nearly a week. It's easy to find out, remove 2 hex nuts and have a replacement gasket on hand.
• Clamping the bypass should not have any effect on water flow under any circumstances so flow rate is not an indicator of the coolant path.
• With a waterlift exhaust system, exhaust backpressure is expected to fluctuate, higher when pushing out a water batch.
• 4000 RPM in gear??
• Please remind me, raw water cooled, right?
• When was the last acid flush performed? Has the water jacket side plate been removed for inspection?

[joe_db]

Redline for an A4 is 3600 RPM, so 4000 is pushing it

[sastanley]

I pulled the engine out and sent it back to the mechanic I bought it from.

So, if the engine was removed (from the boat?? ) and ran great for the mechanic, what is different from his bench test and the boat test? Fuel supply, water intake and exhaust systems.

I also agree with Neil's questions..a few things need to be clarified to actually understand where we are at and where we are to go.

[joe_db]

Can we confirm the engine can swing a 17x12 prop at 4,000 engine RPM
Also can we confirm the engine oil pressure drops right away in forward? Does the reduction gear use engine lube oil? Is it doing something to the oil? Did we ever get oil temps?

[Dave Neptune]

Mark, after reading this thread I think most of your trouble may just be heat. Get a cheap IR temp gun and check the temp of the oil via the oil pan.

If the oil temp is rising more than the water temp as the pressure drops you may just have the oil pressure adjusted to high. Starting cold and at 1500 rpm's what is the pressure? 60 is way to much!!!

Oil being pumped at higher pressures will make a LOT more heat. That with the fact that you are running way to hot on the water side will really add to temps.

Was the block, manifold and head "boiled out" when the mechanic worked on it?

Did you ever turn the key back to on after the engine was stopped at 180* if not do so. Shut it down and wait about 5 minutes and then check the temp, this temp is a far more accurate indication of the "RUNNING TEMP" of the engine in a raw water cooled engine. My ole RWC A-4 ran at about 130 and the 5 minute shut down would yield around 160. Remember a RWC engine is bringing in cold water where a HX is running very warm water into the engine. My guess is you will see over 200* and bingo low oil pressure too.

Dave Neptune

[toddster]

Last night, I happened to browse the Indigo web site and noticed their discussion of oil pressure vs temperature. Note that this is pursuant to a sales pitch for their engine oil cooler. I wasn't previously aware that this was such a problem as to require another accessory!

I was thinking, "Gee, I'd like to see some data on that." The graphs above seem like a good start. But I think we'd really need to see oil temperature, not water temperature.

Quote:
"As designed and built the Atomic 4 has no provision for cooling or warming the oil. As a result, it takes about an hour of operation for the oil to get up to a reasonable operating temperature and continued operation beyond about an hour causes the oil temperature to continue to rise until it gets quite hot and thin. Depending on the condition of the bearings and oil pump in the engine, this is quite often seen as a significant drop in oil pressure."

[joe_db]

Last night, I happened to browse the Indigo web site and noticed their discussion of oil pressure vs temperature. Note that this is pursuant to a sales pitch for their engine oil cooler. I wasn't previously aware that this was such a problem as to require another accessory!

I was thinking, "Gee, I'd like to see some data on that." The graphs above seem like a good start. But I think we'd really need to see oil temperature, not water temperature.

Quote:
"As designed and built the Atomic 4 has no provision for cooling or warming the oil. As a result, it takes about an hour of operation for the oil to get up to a reasonable operating temperature and continued operation beyond about an hour causes the oil temperature to continue to rise until it gets quite hot and thin. Depending on the condition of the bearings and oil pump in the engine, this is quite often seen as a significant drop in oil pressure."

If you have the Indigo filter, it is easy enough to shoot the filter with an IR gun and get your oil temperature. I don't think we know the OPs oil temps yet.
Just FYI, too much under 180 will not be good at boiling off moisture and hydrocarbons.

[clark800]

Lots of great questions, I'll try to answer them all.

The engine is raw water cooled.

The thermostat was removed and there is a plastic cone (a dispenser for silicone tubes) wedged into the bypass hose to block flow. I took the plug out to confirm it is intact. I don't think it forms a perfect seal, but it looks like it would restrict the flow a lot.

The mechanic said he did not do an acid flush when rebuilding the engine, but cleaned all the parts manually while rebuilding. At this point there is only about 5 hours on the engine since the rebuild and the symptoms have been the same since the beginning.

The mechanic said that he did check the bearings and journals. He said that his tests would have caught something if there was an issue there.

The reduction gear does use the engine oil. I don't think it does anything to the oil aside from use it on the gears.

I can confirm that the engine reaches 4000RPM with a 17x12in propeller and the 2:1 reduction gear. I could see the turbulence in the water from the propeller. Of course this assumes the tachometer is working. I believe it is because it sounds like it is idling at 1000RPM, running normally at 2000RPM, and getting a bit scary at 3000-4000RPM.

I don't have any oil temperature reading yet, but after stopping the engine after reaching 180F and leaving the temperature sensor on, the temperature rises to 210F or above.

The oil pressure drops rapidly after shifting into forward only if the temperature is already high. If I shift into forward while the engine is still warming up the oil pressure is maintained.

I do have the Indigo oil filter and previously tried it without any noticeable effect. Adjusting the pressure regulator on the oil filter did not raise the oil pressure after the problem started.

The mechanic was pretty confused by the problem too; he said he's sold many engines and asked the buyers about them and everyone else's run at 130F and go up to 150F after shutoff (versus 180F and 210F for mine). He seemed to agree that the exhaust system is the prime suspect, although without any ideas of what might be wrong with it.

I'll describe my exhaust system in case that raises any issues. Starting from the exhaust flange, there is a 1.25in bronze nipple, then a 1.25in to 1.5in bronze adapter, then a 1.5in bronze nipple, then a bronze elbow pointing upwards, then a Yanmar mixing elbow where the water enters, then an 8in long 2in diameter hose directly downwards to an LSS50 Vetus waterlock muffler, then a 2in hose to a Vetus 2in to 1.5in adapter, then 12ft of 1.5in hose that crosses into the lazarette and initially rises about 4ft then gradually descends down to an elbow connected to the thru-hull on the transom. All the components in the exhaust are new except the thru-hull and elbow. I verified that there is no blockage there.

I tried removing the rise in my exhaust hose to see if it would lower the backpressure. The pressure wasn't noticeably different (perhaps a bit lower, though again really hard to get a single number out of it), and it was still running at 155F in neutral.

@Dave: Yes, the oil pressure starts out at 60PSI from a cold start. This was set so that the warmed up oil pressure would be 40PSI. It does hold at 40PSI after warmup if I stay in neutral. I didn't know that the higher oil pressure would produce a lot more heat, that is interesting. The mechanic didn't seem to think 60PSI starting pressure was an issue. Also, I'm not sure how high initial oil pressure could account for how his tests ran at much lower temperatures. I haven't made any adjustments or modifications to the engine since his tests.

[Dave Neptune]

I don't know what you think but an engine rebuild absolutely should include block, head and manifold cleaning (boiling out).

If you have been running for a while at those temps the block could be salted up good.

Perhaps check the Tee fitting on the side of the cover and confirm it is clear and clear into the block.

Can you guess how much water is coming out of the exhaust? Can run at idle and stick a bucket under the exhaust to see how much water is being pumped. I don't remember how much is supposed to be pumped but someone whose memory is better will probably chime in with the info.

Try completely blocking the bypass too, may glean some info there too.

With the Indigo set up which has it's own pressure regulator be sure the opening where the stock one was is clear. May have something stuck in there causing a good deal of work (heat) for the oil pump.

With good water flow and a clean block your trouble should be getting heat not to much of it. The salts will begin to deposit around 160* or so. The running core temp of the engine is at 210* according to your 5 minute finding~good info.

Dave Neptune

[joe_db]

Taking a look at this, something is very far wrong with the prop and engine RPM.

[ndutton]

Yanmar mixing elbow? This bring's Dave's water volume inquiry to the forefront. They are known to have problems as they age., for example . . .