Questions and Answers

Knocking Mustang Q. Dear Vincent, I have a 1965 Ford Mustang with a 289 V-8, 2 barrel carburetor, automatic transmission with 63,000 miles on an engine that was rebuilt at 160,000 miles. I have meticulously maintained the engine oil and filter replacement, change them at between 2,500 or 3,000 miles or 6 months, whichever comes first.

The car has no A/C, no power steering or no power brakes.

About three weeks ago I started the engine one morning and the following happened:

1. I heard an engine "knock" for about one minute, then it went away. It did not sound like a lifter knock, but more of an engine knock.

2. The car has an oil pressure light. During this start-up event the light went "OFF" immediately after starting the engine as it always has. So, the car did not appear to have low oil pressure.

At the moment I plan on installing an oil pressure gauge.

The Oil Pressure light continues to operate as normal. I will know more when I have the Oil Pressure gauge installed. Please note that I installed a new Oil Pressure switch about 1,000 miles ago.

The oil was in good condition and I was running 10w30 at the time. At the advice of my mechanic I have now changed the oil to 20w50 just after hearing the engine knock.

3. I was suspicious of the engine knock and have been listening for it to occur again during initial morning start-up. It has not appeared during initial start-up since this one time.

4. Slight knock at idle - When I idle the engine up to about 3,000 rpms I do hear a slight engine knock. When I go above 3,000 rpms the knock goes away and when I go below 3000 rpms the knock goes away.

The knock never appears while the transmission is in drive or reverse while driving.

I have taken the car to my mechanic who knows engines quite well. He has advised that I should keep driving the car until the knock occurs at all RPMs.

5. I have read many of the descriptions about rod knocks on the Auto Repair site and have not seen anything describing a similar problem.

6. I have been advised to check the bolts connecting the torque converter and the flywheel to ensure none these bolts have worked themselves loose. Also, this is a good idea as I had the transmission serviced about 2,000 miles ago and I know the mechanic had the torque converter cover off of the transmission while draining the fluid from the torque converter.

Do you have any other advice about trying to isolate the problem?

Thank you,
John

A. When I hear a rod knock, the first thing I want to do is drop the oil pan and feel the rods. If I find one or two loose, I can take the caps off and measure the crankshaft and see if I can replace the bearings without a problem. A lot of times I can catch it before it becomes a major problem.

I disagree with "driving the car until the knock occurs at all RPMs". That's like saying, "Why spend $100.00 to fix it today when it will cost you $500.00 next month?" If you catch this problem early enough, a set of rod bearings is all that it will cost you. Next month it will be rod bearings AND a crankshaft.

A transmission service has nothing to do with the torque converter bolts, but it is still a good idea to check them. Loose bolts there could sound like a rod knock.

Additional Information provided courtesy of ALLDATA