Loud tapping in motor...??? 2000 Blazer

Started the Blazer (2000) the other morning, 5:30 A.M. and immediately it's tapping like an overheated motor, didn't do this the day before. Drove to work, sounded like $ht the whole way. Came out of work, the same thing. Next day, take the minivan to work, come home, start the Blazer...Same...Check the oil, doesn't need anything...check the anti-freeze (I don't know why being this wasn't a warmed up motor, but what the hell), anti-freeze is fine. Start it again, purrs like a kitten....um ok...take it for a drive, get it nice and hot...no problems, sounds like it should. Park it, come out the next morning :banghead: , taps like an overheated motor. Come home from work start it, same thing...move some stuff in the garage, pull it in, shut it off, pop the hood...start it back up, purrs like a kitten...WTF??? :screwy:
Any ideas ??? Suggestions ???

could be you oil pump going bad which is a known problem one of the very few deaths of the 4.3 ... also if my vehicle was knocking i would shut it off immediatly no drive it to work.. get it checked b4 you get perminant damage

Oil pressure is fine...whether it's knocking or not pressure is about 40 at idle and 50+ driving. Just started it again a little while ago, cooled down a bit but not completely....no knocking. I'll let it sit over night and see what happens.

If its lifter noise change your oil (5w-30 high mileage) will help the lifters or add some lifter quiet then change it and use a good filter as it may be clogging. Also look at the coolant reservior very carefully and see if it is slowly dropping after you drive it - classic upper intake manifold gasket internal leaking onto the lifters and first sign of a leak is often lifter noise - you can use the free loaner pressure tester that may prove pressure is dropping and you can't see external leak then intake into valley - you usually see NO water in the oil cause it sprays in as a mist and evaporates before it mixes in the oil.

Did you check for an exaust leak? Sometimes this can make a tapping sound.

Now I'm no mechanic but what happened to me several years ago might be happening to you. Not knowing the makeup of your truck engine this may or may not be true.

I had a 73 Dodge Coronet (about 140,000 mi) that had some knocking in the engine. I pulled off the valve covers and noted one of the lifters was loose. The rod that was there was so loose (and bent) that is would sometimes hit the side of the engine. If the rod just happened to get correctly centered, it ran quiet. Just depended on where it was when the engine was turned off whether it did it again. I replaced all the rods that were bent and never heard it again. I also had a little increase in power since all the valves were then working. I hadn't noticed the decrease in power since the rods had all bent gradually over time. On my 318, the rods were nothing but a straight piece of metal with a ball shape on each end that fit into a depression in the engine and in the rocker type thing on top of it. Probably over time they might have caused some damage but unless they broke and pieces got into the engine block, probably nothing major would have gone wrong.

What oil filter are you using? What oil are you using?

You might have a defective oil filter that is not allowing enough flow through.

Regardless, I would change it just to be sure. Also consider runnig a bottle of engine flush through just before you change it. Put the flush in and regardless of the instructions, idle it for 30 minutes and then drop the oil and replace it along with a filter that is not a Fram.

Did you check for an exaust leak? Sometimes this can make a tapping sound.

I agree, could be the "tapping" , but an exh leak will not usually come and go , it will be there cold, yet disappear hot. I couls see a lifter coming and going like this and definately a wrist pin, but a description of the "tapping" would be the best way to find out. A spark jumping comes to mind as something that can be "tapping" and also can come and go. It is also easy to find it if it is acting up when it's dark out simply open hood and look for it.

If the motor runs bad or misses at the same time as the tapping and it is random it could be something that causes it to not fire, if it is then it can be checked and the faulty cyclinder or cylinders isolated. It may not tell what it is yet, but at least you would have it isolated as to which cylinder is doing it.

Carbon/piece of metal under valve, bad cam lobe, rocker, pushrod, broken piston, ect.

Fram Extra Guard Filter (Looks like that's a bad plan according to most on the board). Castrol Durablend 5w30, been running this for quite some time. The filter was put on maybe 500 miles ago.
I'll try dumping a can of Gunk in it and cleaning everything up...New Filter (Not a Fram) and see what happens.

Instead of using GUNK, go to the dealership, and pick up some GM Engine Oil Supplement. It is approved for use by GM, and it works very well to quiet lifters, and basiclly just clean the engine. If you really want to go the extra mile, pick up some GM crankcase cleaner and follow the directions to flush the engine, before you do the oil/filter change.

Fram Extra Guard Filter (Looks like that's a bad plan according to most on the board). Castrol Durablend 5w30, been running this for quite some time. The filter was put on maybe 500 miles ago.
I'll try dumping a can of Gunk in it and cleaning everything up...New Filter (Not a Fram) and see what happens.

There is your problem bud, that filter will be overly restrictive and will not keep the oil in the top end when it is sitting due to a bad anti-drainback valve.

GM has a TSB about it.

Anything other than Fram will have it much much better.

There is your problem bud, that filter will be overly restrictive and will not keep the oil in the top end when it is sitting due to a bad anti-drainback valve.

GM has a TSB about it.

Anything other than Fram will have it much much better.

While I agree that the fram filter is not a good choice of filters, it does not explain an intermitent tapping from the engine. If that filter was restricing oil flow, you would have the engine tapping all the time.

While I agree that the fram filter is not a good choice of filters, it does not explain an intermitent tapping from the engine. If that filter was restricing oil flow, you would have the engine tapping all the time.

The thing with Frams are they will sometimes be intermittent.

I pulled that filter, put an AC Delco on it, drained about a quart of oil, dumped in a can of motor flush, ran it for about 10 min, pulled that filter, drained it, put on another new AC Delco Filter, Fresh 5w30 Castrol Durablend and so far it's purring like a kitten again and the oil pressure is back up to 60 consistantly at idle or driving.....When I was having the problem it was at 40 idle and about 50 driving.
I'm guessing the whole problem was the filter and for some reason at some of the time I wasn't getting enough oil to the top of the motor, thus tapping. Why it was not ALL the time is beyond me....but so far, so good. I'll let you know if that changes. Thanks for all input!!!

I pulled that filter, put an AC Delco on it, drained about a quart of oil, dumped in a can of motor flush, ran it for about 10 min, pulled that filter, drained it, put on another new AC Delco Filter, Fresh 5w30 Castrol Durablend and so far it's purring like a kitten again and the oil pressure is back up to 60 consistantly at idle or driving.....When I was having the problem it was at 40 idle and about 50 driving.
I'm guessing the whole problem was the filter and for some reason at some of the time I wasn't getting enough oil to the top of the motor, thus tapping. Why it was not ALL the time is beyond me....but so far, so good. I'll let you know if that changes. Thanks for all input!!!

Glad it is smoothed out.

The Fram media seems to lke to collapse sometimes and really restrict flow.

My problem started with the smell of antifreeze. There seemed to be a slight leak somewhere, but could not find where. Then one day I drove my Blazer to the store and when I came back to the vehicle to start it, I heard a knocking nosie that went away in less than a minute. This seemed to happen only in the mornings on occassion when first started. (Not cold mornings either). I then had the oil changed to Mobile One and everything was fine for about a month, now it is doing it again. Someone told me to put an AC Delco oilfilter on and that should do the trick. Tried that with new mobile one and everything seemed fine until this morning. Started knocking again. It seems that it knocks for about 2 to 4 minutes and slowley fades away until no knocking is heard. Any ideas???

Stop using Fram oil filters.