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So I got my compression test results from the dealer today. This is a 57k mile 1995 that I bought March 2017 with just under 50k. The engine has no major symptoms of low compression but it does have high oil consumption (about 2 quarts per 1000 miles). It smokes on startup if it hasn't run in a while but otherwise runs strong and last year had a full vac job and cooling system replaced. I've never had a hot start issue.
Double click to pull the file up. So please note that this is before altitude compensation. At 790 feet that bumps these numbers about 4%. Basically at standard conditions I have around 100psi compression, just over the 680 kPa minimum, on both rotors and it's relatively even.
Any thoughts on how much life it has in it until hot start problems? Another 10k miles maybe? I drive about 5-6k a year.
Mazda changed their min spec from 80psi to 100psi, you will not start seeing hot start issues until you are below 80psi. You could have another 30-40k miles (even more) before that happens, chances of the original coolant seals failing at around 80K are much higher than you reaching enough mileage for low compression to prevent you from starting.
However if you are consuming that much oil it sounds like the oil control seals are on their way out (or the seals in your turbos).
I didn't know Mazda raised their spec, but now that I think about it, 100psi wasn't considered low 10 years ago.
Why do the coolant seals fail at 70-80k on FD's compared to much higher mileage on the older engines? Is it the fan activation temperatures? Thermostat is the same over the years. I know the early production ones had the cooling system recall. Do the later engines (mine being a 95) have the same tendency to lose the coolant seals? A friend of mine got 110k out of his original engine on his 94 and never had a coolant seal problem.
I don't see any smoke on deceleration. It's just that first start up, and it's only a small puff unless it hasn't been started in a couple weeks.
I wonder if the tester and software is based on the RENESIS/MSP values. Even new the REW would never get to the same compression as a RENESIS due to a lower compression ratio.
Oil is going somewhere, if it is not leaking, it is burning. Oil control seal leakage is evident at high rpm not decel, since the oil pressure is higher. Turbos would be decel.
Fan recall harness and controller do not turn the fans on at a lower temp. Do a search.
Failure reasons for FD vs FC range from people never flushing the coolant to the undersized radiator, high fan switch temps, twin turbos, higher power, etc.
Always attributed the shorter average life of our coolant seals to forced induction and the higher temps and pressures.
But I’m curious too. I get the puff of smoke on cold start, but then nothing again unless it sits overnight. No smoke under boost or decel...and very little oil consumption. Working OMP but I also premix at half-rate.
A lot of it is about the lifestyle of the car over time. Highway miles are gonna be easier than stop'n'go or hard driving. They ran the FD super hot to meet emissions standards and at higher? coolant pressures. New builds and new materials have the benefit of hindsight. If you don't have catastrophic problems, well worn compression loss will even out with healthy motors at higher (>250) RPMs. Healthy old motors will go 'til they wont start or wear out a soft seal.
I wonder how far you could take fresh built stock FD with the benefit of hindsight. 150k easy I bet, with reliability mods.
Even though your engine doesnt have that many miles, the seals are 25 years old. They dont last forever.
A good running motor is the most important thing. As stated above, you can likely get another 30-40K out of that engine. I would continue to drive it without worries.
Smoke on start-up will be worse the longer the car sits between drives. This will continue to get worse as the engine ages.
Still have the OMP? I have a dedicated OMP tank and I go through at least a qt of oil in one track day. It also smokes like a pig on cold start up with a relatively recent rebuild (also pre-mix heavily)
^ yeah I still have the OMP. I can't be bothered with premix in the fuel or in a separate tank. When the OMP fails it will go into limp mode and I'll replace it.
Thanks for the feedback guys, I think I'm just going to keep driving it. It's basically what I expected when I got it--not a new motor by any means but still some life in it. I got a little concerned for second until Banzai Racing mentioned that they had changed the standard.
08-16-18, 10:49 AM
