oil pressure/knock 1997 V-6 4.2l

[capwater]

Greetings, new guy here, but I've been turning wrenches for 3 decades.

I have one of the dreaded V-6 motors, mileage 125k. Here are the symptoms:

1. knocks for a couple of minutes at startup, oil pressure reads fine
2. after a few minutes warmup, knock reduces to almost negligible, more of a slight tick, oil pressure still reads fine
3. after about 15 minutes at full operating temp idle will drop when stopped and oil pressure will drop quote a bit (no change in knock status), stepping on accelerator will increase rpm and bring oil pressure back
4. driving i do not notice any drop in power or oil pressure drop, runs fine even on highway at 75mph
5. no oil leak, recent change with filter and no coolant in oil.

Took it into the dealer who promptly said I need a new engine (over $4k), low compression in 2 cylinders was the diagnosis. Called around some other place for engines and talked extensively with a guy who was leaning towards oil pump replacement based on my description of the problem. Logic is I should have noticed a power loss if compression was bad. Surfing around I have seen a similar opinion relating to clogged pickup screen and bad pump. As this is an extra vehicle and just used to run to Lowe's/HomeDepot I can survive with a less than perfect situation and have the time to work on it. New oil pump quoted as $115 for the parts. A new engine really isn't in the budget, I would just sell it as is and get another used truck for a few grand.

Thoughts anyone? Much thanks.

[streethealer]

I'll reply just to give you a bump. My thoughts on your problem are worn main and rod bearings causing you to lose pressure at idle. Since you don't use the truck as a daily driver, I would venture to say that it has many more useable miles in it. If it were mine, I would use a little thicker oil in it at your next oil change and see if it makes a difference. If you use a 5w oil now, try a 10w or 15w oil. I have read that some people use 15w oil and have zero problems with it. I'm not big on oil additives or so called snake oil treatments but if you are maybe they will work for you. I don't think that the oil pump would cause the symptoms that you described. Good luck and let us know how you make out.

[capwater]

Thanks for the reply. An update; as a result of my recent oil and filter change I don't have the bad knock on startup anymore, just a slight ticking which doesn't go away regardless of engine temp. I'll give the 10W oil a shot since it is the cheapest solution out there.

[bokker]

hi, it is good advise using thicker oil so long as it is for a short term solution. my 97 v6 had the same problems and i also had no way out as the truck was needed to run. i took it a stage further and put STP oil addative to really thicken things up. it lasted 2 months but payed the price of a new crankshaft and a full rebuild. good luck bokker.

[monckywrench]

Start looking for a good salvage yard engine you can hear run.

$4K is too high to invest in most trucks that old. Many complete trucks go for that much!
My friend just scored an excellent used 2000 4.2 for $300, which beat the one I found for $500.