5,000 mile UOA after coolant tank failure
2002 9³HOT (T7), automatic, 180,000 miles
Car was bought in December 2008 with 60,000 miles on it. PCV upgrade had already been done. I replaced the air filter with a K&N drop-in panel. No performance upgrades. Based on the T7's reputation for sludge and multiple owners' UOA results at the time, I've always done 5,000 mile OCIs with Mobil 1 5W-40, 10W-40 High Mileage, or 15W-50 oils. All of these are dual rated with ACEA A3/B3. Because I've always followed this "short" OCI schedule, I've never done a history of UOA results like I did with my 1999 9³SE (T5).
Around the beginning of September 2018 my coolant overflow tank's hose nipple broke off. I'd been getting occasional "low coolant" messages but was never low on coolant, so when it popped up again on the SID I ignored it for several days. When I finally checked it I was surprised to see that the overflow tank was empty and the hose was broken off from the tank. I think I was driving three full days like this but I never got an elevated temp on the gauge. Apparently I still had coolant in the system but it just wasn't a full system. I replaced the overflow tank and took the opportunity to drain what remained in the radiator and refill with new G5 coolant.
At that point I was about half way into my 5,000 mile OCI and decided to finish the OCI without changing the oil or the filter. When I reached 5,000 miles I took a sample and sent it off to the lab. I was a little nervous because the sample was very black!
I just got the results back and they look reassuringly normal. The additives were a little lower than I'm used to seeing but viscosity was still good for the 15W-50 and 5W-40 mix I was running (15.8 @ 100°C) and soot, sulfur, and oxidation were all normal. I'm glad I always use the longer filter! In this case it was the Wix 51516. I decided to refill with Delvac 1 ESP 5W-40 (Emissions System Protection) because we're still getting a lot of sub-freezing days here in Northern Colorado. And the new filter is the Purolator-made Carquest R85516. The lab's notes on the UOA are, "Label indicates coolant overflow failure. The compartment wear is normal. No problems indicated at this time."
My OCIs on my 1999 9³SE (T5) were 10,000 miles using zero make-up oil but with changing the filter and topping up the oil at 5,000 miles. I could probably do the same with this T7 engine since I'm constantly adding oil lost thru the leaky turbo seals. My 1990 C900 wasn't a turbo and needed about 1 qt of oil every 5,000 miles. Because I was constantly adding fresh oil, long-term UOA on that car showed I could really go indefinitely (no oil changes) if I only changed the filter every 10,000 miles. (I changed the oil every 20,000 miles just because I felt bad going longer.) I guess I'll have to keep track of how much oil I'm adding to the 2002 9³HOT over the next 5,000 miles. :-)
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