<20 psi oil pressure, blue smoke and rattling noise from the engine

(peder) #1

The engine in this 420G was rebuilt 6 yrs ago. It has been very good until recently.
Today I fired it up after 2 months, and have the faults above in the title. I actually didn´t drive it. Had it running for 15 min., incl 10 m drive in and out of the garage. Saw the blue smoke in the sun. Heard the heavy rattling when standing on the right side and actuating the carbs with the triangle by the firewall. Not even at 3000 does the oil pressure go much above 20, on a cold engine to start with. I have used another sender, with the same results.
What has happened?
I forgot the stetoscope. Could bring that tomorrow, to try and hear if it comesfrom the head or block.

(peder) #2

Went back afterv2 hrs with a stetoscope, but now the metallic rattling was gone. Stable engine at all revs.
Still no oil pressure above 22-23 psi.
Will change the sender tomorrow.
More later…

(Mossback) #3

What oil weight are you running? It’s surprising the pressure isn’t better when cold, how’s the oil pressure when hot at idle? I put some straight 50 weight in a TR-6 I had and that bumped the pressure a lot. I’ve run cars with very low oil pressure, a TR4 that didn’t show any, yet never stopped going, but that would have been a cheap rebuild.

(69 FHC ) #4

Maybe a slightly jammed open pressure relief valve?

(peder) #5

Very good idea. I had this happen on an XK150, with an idle pressure of about 7psi. But it gave perhaps 25 at 3000. Cat remember, Removed the valve and found a 4mm piece of metal that looked like an end bit of a split pin (for locking a split nut).
Will look tomorrow. Perhaps tap the casing around the valve with a small hammer, but doubt that it will free the spring and valve.

(PhilW) #6

One easy check of the relief valve is to remove the bypass hose from the filter housing only - keep the hose on the pan as the oil level might be higher than the pipe on the pan. put a length of hose on the housing and into a pan on the floor. Have someone start the engine for a second or two while you watch the hose in the pan on the floor. If your engine only has 20 to 30 p.s.i., the valve should not open and no oil goes into the pan. If a lot of oil goes into the pan, then the valve is slightly open from debris. Please do not put a clamp on the original bypass hose as a quick way to check the valve, because if the valve is open and the engine builds up it’s usual 100 p.s.i., the entire engine oil pressure system will have 100 p.s.i. without a relief.


(peder) #7

Update: the oil level is almost an inch above the top of the hatched area on the stick, and it reeks of gas. Here is my thought: I had problems with the AED back in October. It ran badly and with sooty plugs. Thought I had sorted the manual cut off switch, but the 5-6 short drives obviously sent a lot of petrol down to the sump. Not nice for the cylinders!
And the litre, at least, of gas in the oil made the total volume so large that the pump could´t give more than 20psi.
I feel so sorry for the engine.
Will drain it all tomorrow and change the filter of course. Pity about oil and filter which were changed on Oct 4th

(David Jauch) #8

Much thinner oil due to the gasoline would explain the rattle, the low pressure due to the lower viscosity and the smoke can be because the oil-gas mix is more or less evaporating at low temperature. The rattle could have gone away due to evaporation and maybe further mixing. If you’re lucky the bores will be fine? The relief valve it is not, if jammed the cold oil pressure should still have been higher (it only ever opens so much, it can’t possibly drop cold pressure off idle to sub 20?)
The pump must have had an easy job, lots of oil rushing in and no pressure from the bearings…

(peder) #9

And now, after 2 hour long drives in the last few days I have to conclude that the car and engine are back to normal (I did mention the obvious oil change I think).
I have been lucly, but then the sad drives earlier were only 1 mile each plus a couple of idlings of a few minutes.

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(Paul Wigton) #10

“after 2 hour long drives in the last few days I have to conclude that the car and engine are back to normal…”


(Mike Spoelker) #11

Reason #47 why avoiding the split pins on the rod bolts is a good idea. A lot of times they trash the oil pump on their way to the oil filter.

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