1994 Mazda 626 Repair Question
Uses oil/smoking on cold startup
Interesting conditions here. Smoking is main symptom, and only occurs on an overnight cold start-up. Does not burn/use oil when fully warmed up. Thus, problem symptoms only happen in open loop operation. No check engine light is displayed normally, and when it does, a shut-off and restart clears the unknown trouble code. Trouble code only appears at the end of the warm up cycle, and not before.
Idle is stable at 750 rpm. Fast idle is about 1500 rpm, and stable.
Smoking will last about five to seven minutes. After that, no smoke. Exhaust smell is very similar to hot tar? Very little oil smell. First appearance of smoke is distinctly whiteish, then then turns a light blue. When the engine is almost fully warmed up, will leave a noticeable oil smoke trail behind.
Oil usage is about 700 miles to a quart. No visible leaks on engine or oil pan. Engine is clean. Engine is also quiet, no ticking or knocking can be heard.
Antifreeze level is stable, and when radiator cap is off, a little pushes out until the fan runs as the radiator gets hotter, and then it drops right back down. Do not see any fluctuation in antifreeze level when run this way. Replacing fluid lost is about 1/8th quart.
Leaking fuel injector? Worn valve guides? Worn rings?
Two years ago, ignitor assembly went out on distributor. Replaced distributor with rebuilt. Did attempt to start car when part failed for about five minutes. Then had car towed to repair shop.
This has been going on for about a month. Seems it smokes more when ambient temperature is lower, say, 30 degrees.
When this happens, shut-down and checking oil level at dipstick shows about a 1/4 quart drop after a severe episode. I let the engine run until the smoke is gone, and it still smokes blue smoke for a minute or two after when running the car down the street.
Sometimes very little smoke appears on cold start.
Sounds like valve seals problems
68 questions asked
Repair would mean either installing new valve guide seals or cylinder head?
6 questions asked
i agree, valve stem seals and possibly worn guides as well, i would get the head overhauled, but a word of caution, if the rings are worn as well (do a leak down test) with the head o/hauled and valves re cut and seated, you may start to burn oil via the rings as well.
26,913 answers provided
Definitely many thanks for both your answers. Both answers are dead-on and directly address the problem.
I personally have never seen this condition before, although I did have a 1976 VW Rabbit 2 door 1.6 4-cyl that smoked a bit on startup and also when upshifting 4-speed manual. That one, I knew, was due to worn valve guides and seals. As it was, it ran only 187,000 miles, which was a lot for that time.
It would seem that additional work would also be recommended. Timing belt, water pump, cam and crankshaft seals, etc., since access is there and the engine is open.
There is a little blow-by with the oil cap off at idle, much more so w/PCV disconnected, so rings may well be going as well. VW had so much blow-by at idle that it actually blew the oil cap out of my hand at the end of it. Mazda is not as bad yet as that.
The difference here is that there is no smoke on upshift on the Mazda 5-speed.
Leak-test would still work on engine as it is, no? Ring condition is what I would be concerned with, and would be the stop on any repair if not in good serviceable condition. I have good hearing and would be able to tell where the shop air was coming out from if that happened. If pressure is stable then I would go ahead and repair the head.
As it is, I got the car free in October two years ago. So, if I can make a go of it, so much the better. It had only 162,000 miles on it then.
Again, many thanks.
6 questions asked