OCI for very high-mileage engine? 235k '96 Maxima

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I have a '96 Maxima GLE, it had 200k when I got it. I've been doing 4-5k OCI's using whatever Autozone clearance oils I've had on the shelf. Castrol Edge 0w-30, Castrol Edge 0w-40, PUP 5w-40, PUP 0w-40, Chevron Supreme 10w-30, those are the ones I remember. Car has 235k now. I just changed the oil today with PUP 0w-40 (the SRT branded stuff) with a Hastings filter. I want to do a Blackstone oil analysis after this OCI, but I'm not sure when to end it. I want it to be representative of the OCI I'd like to do with a top-tier synthetic oil (7500 mi), but I don't want it to harm an engine of this age/mileage by going so long.

I did a compression test shortly after getting it, and I distinctly remember two cylinders being notably low (160-165 psi, vs 190-210 of the other four). So I imagine there's some blowby and other old-engine quirks that might foul up the engine oil more quickly than something newer with fewer miles. I should note that I do not have to add any oil in a 4-5k OCI. It's usually 3/4 qt. low when I drain it; I consider that acceptable and don't bother topping up in between OCIs.

Should I go the full 7,500 mi, or empty it sooner and have that tested before ramping up to 7500? Coming into the cooler season, I went with PUP 0w-40, as I understand it's not really a 40wt, but rather a 30 weight. 7,500 miles would have me changing/sampling in late February or thereabouts.
 
Originally Posted By: shurguywutt
I'd test it at 5k and see what blackstone says. I'd probably not go past 7.5k in a car with 200k+ miles.

Pretty much this. Also most dipsticks are a range of one quart from the add and full marks, so not topping off is acceptable. I'm surprised that your consumption is only 3/4 of a quart every 5k! That's impressive for 235K miles. My dad's 04 E150 work van has 250K+ and uses about a quart every 2k miles. So test it at 5k, and maybe go longer if they say it's okay. I would switch to a quality HM oil and see if that lowers your consumption a little. PP HM, M1 HM, maxlife synthetic. Any of those would work great. Plus HM oils generally have a little extra antiwear additives. They're also usually on the thick side for their weights (except PP HM).
 
I thought the low consumption was too good to be true too, but I've monitored it religiously through several OCIs. There is some seepage past old seals (looks like front crankshaft seal and/or timing cover) but leaves no marks on clean driveway. I drive it 34 miles each way to work and back daily. The low compression on two cylinders has always concerned me though.

It was my mom's car before I got it, so I know the maintenance history fairly well.
 
Given that it's a 96 Maxima with just shy of 400,000 kilometres on it. I'd say you're not doing too badly. The fact that it doesn't drip or blow smoke is also nothing short of amazing. A credit to your mother, yourself and Nissan.

If you want to know where the compression loss is coming from (rings or valves) you can do a 'leak-down' test. Here compressed air is fed into the cylinder with the valves closed. You get a number on a gauge which says 'good' or 'bad.' You can assume that you'll get at least 2 bad readings, but the great thing is you can hear where the leak is occurring. Going even further you could stick an endo scope down the bore and have a look.

Props for continuing to use premium synthetic oils on such a non-classic, and looking after it. A 60kms commute to work each day is a reasonable dive. That's near on 30,000kms each year just to work and back.

Regarding getting samples done. Try to use the same brand and grade of oil at least back to back, and have samples done on both. As no oil change is 100% there is some cross pollution when switching brands / SKU's, thus the first reading will have an error associated with it.

All said and done, unless the Maxima is basically a low cost milk run / work commuter / second car. It may be time to put it out to pasture
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as replacing / rebuilding the engine to fix the compression issue (which will be impacting fuel economy,) will cost more than the value of the car.

Regards
Jordan
 
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My 96 Maxima (actually an I30) has about 275k and I use Edge 0w30 for a year or 10k. I have a Wix on it now, but I will be switching to Fram Ultra from the next OCI-on, because Wix's media cartridge is too dinky, and even the XP will have a tiny cartridge in it due to the bypass valve design Wix uses.

My valve covers look nice and clean
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I would shelve the expensive synthetic oils unless bought on rebate, and go with a good high mileage in full syn or blend starting with MaxLife, Mobil 1, or Pennzoil...
 
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