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Discussion Starter #1
History:
1. Overhauled upper engine. Liners, rings, and valve job
2. Drove 10 miles. Oil pressure gauge dropped from normal to zero. Oil light would come on and off.
3. Grounded oil pressure sending sensor wire, car's oil instrument gauge read the max: passed test.
4. Did oil pressure test with test hose connected to where the oil pressure sending goes: Read zero With engine running for about 5 minutes
5. Engine Oil level good. Oil is clear and clean. No burnt smell.
6. Car runs good except for no oil pressure.

What else do you need to know?
What could be causing this?
 

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crank plug dropped out. You didnt touch the crank / bearings or oil pump? Sounds like crank plug fell out.......

DONT run the motor until you figure this out!
 

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The gauge senders are a known weak link. Test #3 confirms the gauge & its wiring are good. I'm not clear what you did in test #4... Ideally, you would connect a mechanical gauge to get a reliable reading.

Any chance the crankshaft plugs were removed & not re-installed? Or that they fell out?
 

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Discussion Starter #4
crank plug dropped out. You didnt touch the crank / bearings or oil pump? Sounds like crank plug fell out.......

DONT run the motor until you figure this out!
Where is the crank plug and how do I fix it?
(I took the lower oil pan off to clean it. That’s all I did to the lower engine.)
 

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Agree that something is seriously wrong. As ghnl said, the gauge senders are a known weak link; however, the gauge sender isn't your problem if the oil warning light is also flashing. Both senders aren't likely to both fail at once, and even more coincidentally, right after you did the rebuild.

You said that you "Overhauled upper engine", but then mentioned rings & liners. So it sounds like you got into the lower engine (e.g., the block) as well. What was done to the crankshaft and oil pump? Were the bearing clearances checked? How was the oil pressure before this work? What motivated you to do the liners, rings and valve job?

You and I are typing at the same time; I just saw your post #4. How did you replace the rings and liners if all you did to the lower engine was take the lower oil pan off to clean it?
 

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Discussion Starter #6
The gauge senders are a known weak link. Test #3 confirms the gauge & its wiring are good. I'm not clear what you did in test #4... Ideally, you would connect a mechanical gauge to get a reliable reading.

Any chance the crankshaft plugs were removed & not re-installed? Or that they fell out?
#4. I used a new mechanical gage. Got zero on the gauge.
 

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#4. I used a new mechanical gage. Got zero on the gauge.
So we are back to a real problem, not a gauge issue. Crank plugs?
 

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Discussion Starter #8
Agree that something is seriously wrong. As ghnl said, the gauge senders are a known weak link; however, the gauge isn't your problem if the oil warning light is also flashing. Both senders aren't likely to both fail at once, and even more coincidentally, right after you did the rebuild.

You said that you "Overhauled upper engine", but then mentioned rings & liners. So it sounds like you got into the lower engine (e.g., the block) as well. What was done to the crankshaft and oil pump? Were the bearing clearances checked? How was the oil pressure before this work? What motivated you to do the liners, rings and valve job?
I didn't touch the lower engine except for removing the lower oil pan to clean it.

I only did the top engine build because the lower engine should have less wear than the upper. Plus, I found on this site and in Alfa book that owners can do this with the engine sitting in the car, which is what I did.

Oil pressure was good before the overhaul and after. Then about ten miles of driving the oil gauge read zero And the oil light would flash on intermittentl.
 

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Oil pump relief valve jammed open? Either way, pop off the lower pan and see what's laying in it....
 

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I didn't touch the lower engine except for removing the lower oil pan to clean it.
OK, but in post #1 you said that you overhauled the liners and rings. That generally means cylinder liners and piston rings. What do those terms mean to you?

vintagemilano said:
Oil pump relief valve jammed open? Either way, pop off the lower pan and see what's laying in it
Yes, you can do that. And perhaps you will find a crankshaft plug or two in the lower pan. Or you may find nothing. But:

#1, You can't access the oil pressure relief valve just by removing the lower pan. You'll need to remove the oil pump to get at the relief valve.

#2, Even if your crankshaft did lose an oil plug, that shouldn't result in zero oil pressure. Yes, oil pressure would drop, but a lot of Alfa engines have run for many miles with a missing oil plug.

I predict that your engine is going to have to come out and get disassembled in order to diagnose and fix this problem.
 

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Jay, the crankshaft has 5 main bearings but oil is only sent to #1, 3 & 5. #2 & 3 mains are oiled from passages drilled in the crank from the other bearing locations. When the passages are drilled, the open ends are closed by Aluminum plugs pounded into the outside openings. There was a raft of instances of these plugs coming loose way back in the 1970's and this still occasionally happens. One solution is to have the crank drilled & tapped so plugs can be screwed onto the opening, but this required disassembling the engine. You may have lost one or more crank plugs and, while difficult, you might be able to remove the entire oil pan to view, or even replace, plug(s).

Where is the crank plug and how do I fix it?
(I took the lower oil pan off to clean it. That’s all I did to the lower engine.)
 

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yeah, so lets assume lower end is ok -- for now --- That means that all the oil pressure lost is on the top end. did you replace the camshafts with the correct cam caps? Check your coolant -- is there oil in there? DId you torque the head properly? I know this is a lot to consider but, low oil pressure is a bad thing -- especially if you get the Low Oil Pressure light to come on.

EDIT -- I guess if there is a ton of junk blocking the oil pump inlet screen this might happen--- drop the pan and take a look ---? You did not touch the oil pump at all?
 

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Discussion Starter #14
OK, but in post #1 you said that you overhauled the liners and rings. That generally means cylinder liners and piston rings. What do those terms mean to you?
New cylinder liners and piston rings.
 

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Discussion Starter #15
yeah, so lets assume lower end is ok -- for now --- That means that all the oil pressure lost is on the top end. did you replace the camshafts with the correct cam caps? Check your coolant -- is there oil in there? DId you torque the head properly? I know this is a lot to consider but, low oil pressure is a bad thing -- especially if you get the Low Oil Pressure light to come on.

EDIT -- I guess if there is a ton of junk blocking the oil pump inlet screen this might happen--- drop the pan and take a look ---? You did not touch the oil pump at all?
The cam caps, meaning the top parts that hold the cam in place, I was careful to install them in the exact location over the cams as before the overhaul.

I'll check the coolant and remove the pan tomorrow.

I torqued the head bolts to specs.
 

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Oil filter plugged solid? I don’t know what from, your oil pan drain plug would be a Christmas tree.... The filter should have a relief valve internally too.
 

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Discussion Starter #17
I drained the oil and slimy sludge came out! So I found the problem thanks to your suggestions!
How hard is it to remove the oil pump to clean it?
 

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yeah so your head gasket is leaking coolant into the oil most likely. Has coolant level dropped? If not, its possible that you can clean up the sludge but oil doesnt just go sludgy all by itself...
 

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Discussion Starter #20
Well, in the interest of helping someone else, I'll embarrass myself and say it looks like a slimy paper towel. One must have fallen into one of the open cylinders and down to the lower engine unbeknownst to me when I was doing my intensive top engine cleaning. 🤪
 
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