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Cylinder compression check


brmurph

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I had to replace my blower motor so while I had easy access to the plugs I went ahead and did a compression check. Turns out it was a better idea then I thought as I had two loose spark plugs, loose enough that the plugs were black compared to the others but tight enough that they did not blow out (less then a turn or so loose). The reason I did the compression test is because I am now burning a quart of oil every 800 miles (this motor has always consumed oil but I use to get at least 2300 miles per quart). Not sure but it seems I really started going through oil when the dealer installed timecerts for blown head gasket at about 99300 miles, I now have about 135000 miles.

Anyway the lowest pressure after 5 cranks was 180 and the highest was 188 which I thought was outstanding at this mileage. Also the first crank pressure was a low of 107 and a high of 118 (not sure exactly what this says but I have heard its good to check :-). So my question is how useful is this info for oil consumption? Seems odd that I am going through so much oil with such good compression. Could the oil rings be gummed up yet compression is still good? I have been on this board for a while (all the way back to Guru) so I understand the WOT procedure and do it often but consumption continues to get worse.

Any chance the loose plugs caused some of the oil consumption? I did have an oil anaylisis done last oil change and the only thing they found that was odd is he said the oil was equivalant to 20 weight oil, I use havaline 10w30 so this made little sense to me but maybe that is the reason for the consumption.

Thoughts?

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How is the driveability?, if you have a leaky injector, you could be diluiting your oil...

Check for leaks

Change your PCV, it could be sucking oil

Did you recently have an oil light at idle? Mike

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1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

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How is the driveability?, if you have a leaky injector, you could be diluiting your oil...

Check for leaks

Change your PCV, it could be sucking oil

Did you recently have an oil light at idle? Mike

Drives great.. Very small leak and it just started recently (sometimes a drop or two on the garage floor). No oil light (thank goodness:-) PVC valve has about 30,000 miles and looks clean (no oil), putting in a new one today anyway. Leaky injector is a thought but I would have thought Blackstone laboratories (oil analysis) would have picked that up (might be worth a call to Blackstone), I will double check the report (when I find it)..

I guess I thought the oil consumption has been because of rings all this time, now that I see good compression I start to wonder.

Thanks!!

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Does it have any blue smoke on hot restart after setting for 30 minutes or so?

If so... it COULD be valve guides, but that would be very unusual.

With compression THAT good... hard to think it could be rings.

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Does it have any blue smoke on hot restart after setting for 30 minutes or so?

If so... it COULD be valve guides, but that would be very unusual.

With compression THAT good... hard to think it could be rings.

None that I notice, the only time I see something come out of the tail pipe is when I haven't done a WOT for a few hundred miles, then I see quite a bit.

Thanks.

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Sorry, I overlooked the Blackstone oil analysis. So how is the oil getting from 10W30 to 10W20?, that would cause consumption. What make of oil are you using

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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Sorry, I overlooked the Blackstone oil analysis. So how is the oil getting from 10W30 to 10W20?, that would cause consumption. What make of oil are you using

That is what I am wondering (expecially since the oil analysis showed no contaminants:-) I am sending in another sample now and will be sure to ask that question. I was using Havaline 10w30 but I just switched to Vavaline 10w30 (yesterday) to see if there is any difference. If not I think my next swtich will be to 15w40 Rotella (should be OK I would think in Texas).

After doing some reading on the net I am starting to think that Texas Jim might be right with the valve guide theory, that would explain the good compression (I think) but not the low viscosity :-(.

Thanks.

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From the oil analysis... sounds like the oil is breaking down.

Probably a smart move to change brands and then have it tested again.

Like you, I am in Texas also. Factory recommended oil for my car is 5w30. I don't like that. In the heat we have in Texas :D ... I feel that it should be at least 10w30. :D

I suppose it could be POSSIBLE that the oil ring is gummed up and causing the oil consumption...but it seems odd that it only started when you had the timeserts done.

Did you have a lot or overheating before the Timesert job?

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Did you have a lot or overheating before the Timesert job?

Not really. I just finished my WOT procedures as prescribed by the Guru and just pulled into the garage when the message came on that the engine was hot, within 10 seconds or so it went from idle engine to camel mode (I was suprised how fast it escalated from the simple overheat to camel mode (260 degrees I think) at which point I turned it off immediatly and called the dealer to tow it in for the timecert replacements.. Again that was 35000 miles ago..

Thanks.

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Got my second oil analysis back and found the level of additive to be lacking (TBN which includes ZDDP as I understand it). If you look in the attachment you will find two results, the first column is the current results where I used the new formula of 10w30 Havoline as you can see the TBN is very low (.8). Continue on to the 3rd column and you will see that I had more miles (7000 vs 5000) on that test using the old formula of Havoline (more ZDDP) and you will see that I had plenty of TBN left (5.0).

I guess the moral of the story is that I should be happy I have to add a quart of oil every 800 miles now that the new oils have the reduced ZDDP otherwise it looks like I would be running out. I guess this is something to note for the older Northstars out there (I wonder what the numbers would be for those that don't have to add oil) not sure exactly what can be done but I have heard that GM brought back EOS (ZDDP additive) recently, I might have to go pick some up..

BTW I still can't figure out why I have low viscosity :-(.

OilReports2.pdf

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