Brief Knock at Start-Up, Then Low Oil Pressure at Idle When Warm

The last time I heard someone recommend straight 30 weight oil for a car, it was Tom McCahill in the pages in the 1960s in the pages of Mechanics Illustrated and he was laughed at then.

A car engine does not have a lot in common with your worn out air cooled lawnmower and to suggest that an engine that is still running at 265,000 miles has had poor maintenance is silly.

Actually with the engine at 226k miles, if the rod bearings are knocking I really doubt the mains are far behind.

Why not? My family has several vehicles over 100k miles still using the recommended 5W-20 with no knocking or consumption problems, and I am sure we are not the anomaly.

Any real evidence to support this? SAE 30? This ain’t the 60’s anymore. Quit living in the past, life moves fast, try to keep up.

At over 200k miles if I had to have a minivan I would would go with 10-30 or maybe 10-40 oil, and change it every 4-5000 and drive it till it dies. Otherwise I would dump it as soon as I viably could.


As I recall Tom always recommended going one weight higher than OEM specifications. Many of his ideas were okay in the 50s&60s, not so good now.


Variable valve timing is the only reason that I know of that prevents the use of thicker oil. It becomes a problem when the engine warms up. All engines that can be started in freezing weather have to be made to handle thick oil. The difference between 5W and 10W is probably less than 20 degrees F.

I always enjoyed reading Tom McCahill’s columns. He had that rare style of writing that was entertaining, even when the subject was car reviews!

Of course a lot of the ideas back then could not be applied to today’s cars.

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In his book, “What You Should Know About Cars”, Tom McCahill not only recommended going one viscosity higher than recommended by the manufacturer, but to stay away from multi viscosity oil. He said that 10W-30 was a lousy number 10 and a lousy number 30. He also didn’t like detergent oils. He said he preferred detergent in his bathtub but not in his crankcase. He said that by holding the particulates in suspension, these particulates were being forced through the engine bearings. He preferred that these harmful particles settle to the bottom of the oil pan where they would drain out with the oil when the oil was changed.
He thought the only reason for multi viscosity oil was so service station owners wouldn’t have to stock every viscosity from #10 to #50. He thought detergent oil came along because car makers went to hydraulic valve lifters. He preferred solid tappets.
I liked reading Tom McCahill’s writings, but I thought his advice was out of date even when his book appeared in 1963. By that time, splash lubricated engines had disappeared.


I think I had that book, or one similar. I do remember the cover photo was of Tom testing a Studebaker Golden Hawk.
I still have some old Mechanix Illustrated with Tom’s articles.
Remember his pre-seatbelt advice: head for the cellar?

I’ll just add that I have had cars with many hundreds of thousand miles, up to 500:000, and I have never had an oil pump problem. The only time I ever touched one was repacking it with a timing chain repair. It would be the last thing on my list.


Uncle Tom had the best similes of any writer. On testing the '59 Bonneville “has a ride smoother than a homecoming queen’s thighs”. On testing the '58 Chrysler “the Windsor corners flatter than a bookkeeper’s chest”. Only he could get away with things like that.


He had a car advice column at one time, and my favorite response of his was to a woman who said something like…
When I got my VW Bug up to 75 mph, I heard a strange squeaking noise. What was it?

Uncle Tom replied, “That was the sound of the Gates of Hell opening”.


Well, I don’t know about fixing anything, but I replaced red bearings on a '64 Rambler American (stop laughing) flat-head 6. It has been 50 years ago plus but it wasn’t but about 2 weeks until the main bearings started knocking. I think I would try the thicker oil, at least in warmer weather, and maybe let it warm up a minute. I’m afraid the days are numbered.

However, I bought an -83 Crown Vic with a sludged up 302. Changing the valve cover gaskets, I thought I would watch oil flow for a few seconds before putting it back together. Slop that ran down on the manifold flashed. I tried to beat out the flames with an old coat. My youngest daughter was standing on the porch with her mouth wide open. “Go have Mom call the fire dept.” Well, I got it out and went to call of the volunteers. My wife took to shoveling dirt on the once burning engine and completely buried the rocker arms. I cleaned it up again, changed the oil and filter and drove it about 100 miles and did another oil change. After 1000 miles, I changed it again. That car developed a knock upon starting that lasted a few seconds and stopped. I traded it in only to have a friend buy it off a used car lot. MOnths later, after we finished our degrees at school, he left town driving that Crown Vic, happy as a clam. I have no idea how long it ran…

If I had your 15 year old van with 226K miles on it, and wanted to keep it running for another two years, and didn’t want to invest a lot of money in it, I would consider all options “bandaids”. It’s likely you’ll be able to get another two years from the car, but no one can say for sure.

I would likely try:

  1. First, as Tester noted, connect a mechanical oil pressure gauge to the engine. See what the “hot oil” readings are at idle and at 1500-2000 rpm. Verify the engine can hold pressure. If it can’t, and it’s way off, then ignore the rest of these bullets.

  2. See if 5w-30 helps. If not, then try 5w-40. I don’t believe your engine has VVT, so even a 10w-40 should be OK.

  3. Try a different brand oil filter for the initial 2-3 second knock. That’s a separate problem than the “oil light on at idle”.

If the mechanical oil gauge check shows your engine can’t hold oil pressure, then you have a decision to make.

  • You could try going to a 10w-50 oil. I’ve even seen cars use 2-3 cans of STP or similar thickener added to them. (As Dylan said: “When you ain’t got nothing, you got nothing to lose.”)

  • You could try new connecting rod bearings. It’s a long shot and still a bandaid because other bearings and journals may be equally worn, but they require the least amount of labor (do it on your back with the engine in car) and can be done for little money.

I’ve slapped new connecting rod bearings on old worn cranks in my past. It’s always a “try it and see” low cost approach on an engine that isn’t worthy of a proper rebuild.

All the best. Let us know what you choose to pursue, and how it works out for you.


Try 20W40 and see what happens.

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If the gauge shows low pressure WITH knock, the bearings are worn. About 150,000 mi overdue for a dodge…
I would pull the pan and rod cap(s) and see if the crank is OK. If it is, I’d throw bearing inserts at it. Otherwise, it’s junk.
On the other hand, if it’s knocking when cold and then knock goes away, it’s likely the upper end loss of pressure - camshaft(?). In this case, I wouldn’t even bother.

I asked the mechanic who usually services our vehicles to listen to the engine and take some oil pressure readings. These were taken with the engine idling:
Engine cold: 15-20 PSI
Engine hot: 6 PSI
You can hear the knock (more of a rattle) at start-up for two seconds, then the engine quiets. However if you slightly rev the engine, and then back off the throttle, you can induce the knock/rattle sound. The mechanic said he never had any long term sucdess changing rod bearings. He suggested a heaver weight oil and using the vehicle as a local driver until I get rid of it or the engine fails.

I live where roads are salted. The van has rust, so I would not do an engine swap for that reason. Since I have recently put new parts in it, I will just drive it until it fails then replace it.

I disagree. You seem to be suggesting if you cannot perform one maintenance task, then do not attempt any maintenance. The range sensor is located inside the transmission. You remove a valve body assembly to access the sensor. I do not feel comfortable opening up a transmission other than to change the fluid and the filter. I replaced the struts, shocks, water pump, radiator, plug wires, spark plugs, and other components, so some things are in my skill set.

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I expect what Nevada meant is that if a $400 shop repair bill is too expensive for your vehicle repair & maintenance budget, then best bet is to replace the GC w/a newer vehicle. Occasional, and increasingly frequent $400 repairs to be expected as vehicles age beyond 10-15 years old. You are right that a valve body repair is not in the typical diy’ers driveway-repair domain.

If that is the case, then my including the cost of the repair made my writing unclear. I was clumsily attempting to say that it has been my experience that the frequency of needed repairs can increase to the point either you or the shop is working on the vehicle monthly or every other month - in addition to normal maintenance.

I put 10W-40 weight oil in the van. The oil pressure light has not illuminated since then. I use the vehicle for transporting dogs to the park and home and yard supplies and will limit it to local driving.

If you ever change to a Motorcraft filter, I would love to hear the result.

I think an extended trip might be a good thing.

With such limited use, this vehicle should last ten years.

Oil filter selection doesn’t matter, valve clatter during start-up is not an indication of failure.

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