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Engine knock when starting - until oil pressure builds up


splashchris's Avatar
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09-23-04, 09:01 PM   #1  
splashchris
Engine knock when starting - until oil pressure builds up

All,
I recently purchased a '95 Chevy G20 conversion van with 115,700 miles on it. The engine runs smooth and I didn't notice any problems - until I changed the oil. I live in S Florida and put in 10W-40 for engines with high mileage.

Now, there is a fairly loud knocking sound when starting the engine that clears up as soon as the oil pressure gauge registers an increase in pressure. The only time the knocking does not occur is when I shut off the engine and then restart it again - with little time delay between off and on. If I wait a half hour then restart, the knocking returns again.

I replaced the oil filter again and put in an oil additive, at the suggestion of the auto parts folks, with no success.

I'm suspecting something with the oiling system, as I would expect there to be sufficient pressure during initial engine crank to supply oil pressure to the lifters, etc. Not sure where to go from here, though. I was thinking of going back to 5W-30 oil, as it's a bit thinner.

Open to all suggestions...

Thanks in advance!!

Chris

 
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09-24-04, 02:47 AM   #2  
hard to say what the noise may be you may have to take it by a shop so they can listen to it after it sets when you start it up, I would suspect a rod bearing with excessive clearance to be causing the noise and while you can try changing the oil back to 5w30 I dont think you would notice a difference if it was a rod bearing.

 
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09-24-04, 02:56 AM   #3  
There is a reason they recommend 5W-30, it builds oil pressure quicker on a cold start.

Change back and use the correct OEM filter (I think it would be A/C Delco)
and see what that nets. You didn't have a problem till you changed the oil.

 
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09-24-04, 04:49 AM   #4  
Of course the other possibility is that the previous owner knew he had some worn bearings and had some 90w in the engine to keep things quiet......

 
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09-24-04, 06:22 AM   #5  
Thicker oil takes longer for the pump to pick it up and fill the oiling system. Therefore contributing to dry starts.

They went to lighter oils to combat that. Besides better fuel economy.

 
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09-24-04, 12:13 PM   #6  
try lucas oil treatment. couldnt hurt.

 
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09-24-04, 08:45 PM   #7  
splashchris
Thanks to all who made suggestions. I put in Lucas oil treatment and replaced the oil filter with a Fram PH-5. The knocking is still there on initial startup - not as bad (I think) - and goes away with increase in oil pressure.

I did notice that the engine seems to run smoother. It doesn't hesitate at higher speeds like it did previously. I think I'll try the 5W-30 and see what happens, since that's what the oil filler cap recommends.

As for a possible clearance problem with the rod bearings, wouldn't the cold start knocking have been present prior to the oil change?

Chris

 
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09-24-04, 08:47 PM   #8  
splashchris
One thing I did notice is this:

When I replaced the oil filter with the Fram, I filled it with oil first. When I started the engine there was no knocking.

This got me thinking....

Could the external oil cooler be syphoning oil from the filter, thereby creating an "empty" oil filter on cold starts???

Chris

 
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09-24-04, 10:00 PM   #9  
I dont think ive ever seen an oil filter get siphoned out by an oil cooler and manufacturers usually will use a check valve sometimes incorporated in the filter if it was possible for all of the oil drain out of the filter also you probably noticed oil running out when you unscrewed the oil filter indicating there was oil in it. most additives while some of them can clean out passages and possibly help a noisy lifter they will not help with clearance problems.
as per when the problem started there is no way of knowing what happened for sure but it is always a good idea to add oil to the oil filter if the filter is mounted in a way to allow you to do so. if it is a bearing it may have started making noise anyway and may not even be related to changing the oil.
you really did nothing wrong by using a slightly heavier weight oil on this engine and it shouldnt of resulted in any serious problems if the engine was new and clearances was out of spec such as not enough clearance on one bearing then the 5 w30 would of been more capable at providing better lubrication to the tighter clearances of that one bearing.
this being a 95 model with 115000 miles on it im sure it has had plenty of oil changes with 10 w 30 or 10 w 40 put in by lube shops in its life instead of the recomended 5 w 30.

 
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09-25-04, 01:18 PM   #10  
splashchris
Bejay,
Since you mentioned it, oil did leak out from the filter when I changed it, so that shoots down the empty filter theory. It is quite possible that the prior owner knew it was acting up, hence the sale. Considering the shape the vehicle is in, I was surprised that anyone would have it up for sale. Maybe I'll be faced with some costly repair bills in the not so distant future.

For peace of mind I must determine the seriousness of the problem. It's going to replace a 2001 Toyota Highlander as our family's daily driver, so I need it running in top shape - especially since my wife will be driving it most often. Honestly, if I could afford to keep up the payments I'd never get rid of the Highlander. Without question, it's the best car I've ever owned.

Other than a local garage, do you know any reputable chain repair shops that have a good reputation I could take the van to for diagnosis? I'm thinking maybe Sears, PepBoys, or GoodYear centers. Any thoughts?

Chris

 
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09-25-04, 02:09 PM   #11  
I think I'll try the 5W-30 and see what happens, since that's what the oil filler cap recommends.
Did you put the 5w-30 back in?

Think there is a reason why they put that notice on the oil cap?

 
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09-25-04, 03:27 PM   #12  
splashchris
I haven't put the 5W-30 back in yet. Today has been hectic with preparations for the hurricane (I'm in S Florida). Tomorrow, if the weather is clear, I'll put the 5W-30 in and report back.

Two questions first:

1> Should I replace the oil filter again? The Fram filter has only been run for about an hour since it was installed.

2> Should I put in another bottle of Lucas oil treatment as part of the oil change?

Chris

 
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09-25-04, 04:30 PM   #13  
I would replace the filter. I wouldn't use a Fram, one of the cheaper made filters.

Can't go wrong with OEM, always the right valving etc for the vehicle.

Skip the "snake oil". Just a good quaility oil

 
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09-25-04, 08:31 PM   #14  
Posted By: toyotaman11769 I would replace the filter. I wouldn't use a Fram, one of the cheaper made filters.

Can't go wrong with OEM, always the right valving etc for the vehicle.

Skip the "snake oil". Just a good quaility oil
What Toyotaman said. Get the Fram filter off the vehicle and use an AC if available to you or if not a high quality filter like wix.

 
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09-26-04, 04:25 AM   #15  
splashchris
Car nut,
I put three filters on in less than a week. The first two were Wix. The auto supply employee (ex mechanic), said to use the Fram. I can try an AC Delco, but at this point I really doubt the filter has anything to do with it. If anything, the Fram filter made the startup quieter, even though cheaper in quality perhaps.

A few previous posts suggested the problem could have been pre-existing, and draining the oil amplified the problem to where it was noticable. Hopefully the weather will hold today, at least long enough to try the 5W-30 oil.

Heck, it's easy enough to change, so I don't mind using a thinner oil that requires more frequent replacement.

Chris

 
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