My 1997 Toyota Prado Landcruiser 2.7 - it still runs...!
Old cars, especially those made by Toyota, seem to have an extremely long life. While performance is nothing to shout about (excluding the real performance models like the Supra, MR2 and AE86 that never made the mainstream here in Malaysia), Toyota's are known and proven for high reliability.
My Prado as above still runs (of course, having taken over the upkeep and taking good care of it does help), of course with some squeaks here and there, but then don't forget that this is, after all, a 20+ year old car with 400,000+ km on the odometer. Not gone for hardcore off-roading like my buddies in the Puma 4x4 club, but I do use it for getting out for light field-work and also to transport larger-than-normal stuff that would not fit into a regular car.
Now, the 3RZ-FE 2.7 liter engine at its heart was designed for a min RON 91 fuel, which is way below the RON 95 minimum fuel sold at the pumps in Malaysia today. Those of you from "my time" and before will know, once upon a time, we did have RON 92, which was the cheapest fuel on the market, but was discontinued (possibly as Proton's with their Mitsubishi engines, needed at least RON 95, while my Honda Civic FD2A could live with RON92, see my post from 2008 HERE and also HERE). So, as is general knowledge, there is no advantage to using fuel of RON higher than the engine was designed for. Or is it...?
Since as long as I can remember, driving the old Prado I always had to be a bit careful when shifting or when accelerating at low RPM's. There is a tendency to jerk just as the clutch was let out completely when changing gears and stepping on the gas. Same goes when the car is in gear, then you let off the gas completely and then stomp on the accelerator pedal. I always thought this had something to do with the age of the car, so anyway, even consciously adjusting my driving style, it was nigh impossible to avoid the jerks, which seem to be coming more from the engine or exhaust rather than the transmission.
Last weekend, went to my usual favorite Caltex gas station for a partial fill up. Normally I would always fill the tank up to full, but since the current COVID-19 pandemic had significantly reduced travelling, I only put in enough gas to go ~1 month between refueling. This was to avoid "stale gas" (will write another post on my experience on that topic soon). Back to the gas station. So happened that the pump that I was at could only dispense RON97, as the RON95 pump was under repair. Rather than drive over to the next pump or go to another gas station, I just decided to go with the RON97, which was priced at RM2.60 per liter. RON95 is currently capped at RM2.05. Partially filling RM41 worth of fuel (slightly overshot original target of RM40, hence round up to the next Ringgit), that get's me ~15.7 liters of fuel, as opposed to 20 liters if I had used RON95.
Starting up and driving away, I noticed that that the ride was now smoother and without the jerk at each gear shift. Also from complete foot off the accelerator to moderately depressing halfway to the floor, is smooth as well. After that, did some short driving around a few kilometers to confirm. Definitely not a placebo effect, and in the first place I was not expecting any difference.
Once home, tried to do some research online, but majority of what turned up is the usual "no need for premium fuel unless you have a <insert high performance car of your choice>". Only one Youtube video which a helpful chap described a plausible explanation. For old engines, the carbon build up in the cylinders could have artificially increased the compression ratio, which may cause detonation / knocking under heavy load / high temperatures. Since this is Malaysia, where temperatures are anyway always high, the heavy load situation could be as encountered during the initial stepping on the gas pedal.
Normally, I don't believe things without evidence. Here I have an observation, and am trying to find an explanation. So, where to go from here? Will continue to try out if this is consistent, until the next refueling run. Then, I could try to go back to RON 95 and see if the problem recurs (and then if RON 97 can eliminate the problem), therefore successfully being able to turn-on / turn-off the problem. If that is the case, then moving forwards there are only 3 choices - 1) Switch permanently to RON 97, 2) Revert to RON 95 and hope this does not impact the life of the engine, 3) Send in for cylinder decarbonizing and then start testing RON 95 again.
At least for now, decarbonizing will need to wait, as due to travel restrictions I'm not able to drive down to Desmond's place @ KL Auto to get it done. If indeed this is the actual root cause. Will post further updates on the situation.
Does any of this make sense? Anyone out there have any similar experience or opinions to share?
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