Hi, My car (toyota petrol 1.3) does a smallish mileage in a year say around 5000 miles, mainly on fairly short distances around town. what would be the 'time' limit to reasonably extend oil changes for economy reasons using a semi synthetic oil ?
I suspect a lot of people will immediately say don't economize in this way. However some forty years ago I had a conversation with a professor of an engineering college and he said engine oil does not degrade 'time wise' as fast as most people think ( and importantly as the oil companies would wish us to believe). So by how much time could one reasonably delay an oil change with modern oils?
I think oil and engine technology has changed somewhat over the past 40 years, so your conversation may not have much relevance :-)
I don't think the issue is one of time related degradation, more the assumption that a car that does a low annual milage will mainly be doing a lot of short trips. The problem then is that the oil is never sustained at an elevated temperature, so contaminants remain in the oil. Of course, if your low annual milage is done by virtue of only a few long trips it may not be such a problem.
I have seen this, where a car doing a lot of short trips goes on a longer journey. The oil level will be OK before leaving, but may drop below the minimum during the trip as the the condensation boils off.
The rule of thumb for a car doing low annual milages is to halve the service interval. In your case, I would at the very least do an oil and filter change once a year. The cost of this when viewed against the total cost of ownership is very small, especially if you are able to DIY it.
Your problem has to do with oil contamination not mileage or oxidation. If you don't get the oil up to engine temp ( somewhat over the boiling point of water for the oil, but I've never measured it ), condensates will accumulate in the oil. Gasoline, water vapor, who knows what from crankcase fumes. Pretty soon, if you never let your engine run long enough to boil off these volatile condensates, you've got acidic crap pumping through your engine that is going to dilute the lubricity and other wear-resistant characteristics of the oil, which will lead to early engine death.
So you have to change your oil just as often as anyone else, but for the contamination reason. You'll have pea soup in the oil sump eventually, or worse, gunk that will clog the minute oil galleries that lube the piston bearings and piston pin ( I call it the pin...the rod that the head pivots on ).
Say at least every 6 months, every 4 months would be better.
Otoh, I'm using full synthetic, and am going by miles not time...5,000 miles change filter and add oil to bring up to full mark on oil stick ( say just less than a full quart for the filter ). And at 10K miles a complete oil and filter swap.
For me, that means a new filter and somewhat less than a full quart at
25,250 miles, regardless of how long it takes me to get to that mileage. Then at 30,250, I change ALL the oil and put on a new filter again.
Well I always buy a car from new, and keep it 7 or 8 years, typically doing
100 - 130k miles over that time. Never have them serviced, and just keep the fluids topped up. Haven't 'lost' an engine yet. How many car breakdowns do you see by the side of the road due to 'inadequate oil changes"? Yea you might get a bit of extra wear, but hey, an engine will be scrapped typically before its 150k mile birthday, well before its expiry date.
This is all myth and magic to get punters to shell out on expensive oil and spares.
As long as you keep all your fluids topped up it'll be fine IMHO
I revcently had this argument with a Mercedes main dealer. I have one car that does very little mileage. Thier position is that its not "10,000 miles or one year whichever comes first", its every 10,000 miles. So the car should not be serviced until the indicator on the dashboard says so. They say its because of the more modern engine oils. Personally I would rather pay for an oil change every year regardeless of anything else that needed done.
EXTEND? You must be kidding. You surely mean REDUCE?
On a low mileage car used on short journeys you need to be changing the oil MORE OFTEN, not less. If you are doing 5000 miles a year then once a year is about right.
Conor ( snipped-for-privacy@gmail.com) gurgled happily, sounding much like they were saying :
I'm sure - but you forget that few cars are scrapped these days because of engines being knackered (or body rot) as they used to be. These days, it's usually a multiplicity of small knackered bits that kill a car. A bush or three here, an exhaust, a couple of tyres, an ABS sensor, maybe a heater matrix or a rad. Perhaps a windscreen or a broken tail light or a bent wing.
One MOT fail that's going to cost £500+ on a car that's worth less than that with an MOT.
A car engine will, indeed, typically be scrapped before it hits 150k. Because the car it's in is scrapped.
For short trip use Semi synth does not allow extended oil change intervals. Fully synth doesn't either. They both offer advantages to people doing higher mileages with fully warm engines. Oils use additives which neutralise acid build up and help keep carbon particles in suspension, over time these degrade, stop working and will eventually dump sludge. Synthetic oils and blends are less dependant on additives to maintain the oil's lubrication properties over the whole period. But it's not the life of the additive package that limit's short trip use.
As Chris said it's contamination that won't boil off. It gets into the oil from blow by of raw fuel and water vapour. A lot of fuel gets past the rings during starting and warm up as it's running very rich and fuel doesn't vaporise well in a cold engine. Your short trips won't get the engine to full working temp, it takes about another
10min driving (not idling at lights or in stop start traffic) after the water gauge points at normal for it to be fully warm. So you won't boil this fuel and water out of the oil, it just accumulates. Fuel and water are not good lubricants for your engine's bearings. Water is better than no lube at all but fuel is very poor it washes the oil off the bearings.
Read your owners manual for the "maintenance schedule", look for the bit "severe driving conditions", and have car serviced as listed under "repeated short trips". For UK use even in present cold snap you can ignore anything about "repeated short trips in extremely cold weather" that refers to USA East coast and continental Europe with temps below
-10c all day. Most makers consider your usage abuse and recommend additional oil changes.
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He may have been right on the time factor, but it's the short journeys that cause a build-up of condensation, which is not good. You want to change it more frequently rather than less. Every 6 months would be ideal, but with a decent quality modern oil you'll probably get away with every year. But for the minimal cost of an oil change, do it every 6 months and keep it in tip top running order.
As the professor said, the oil doesn't deteriorate very much with time. It deteriorates if it is moist, or if it is overheated. Gasoline in the oil doesn't cause chemical deterioration as much as it drops the viscosity greatly and reduces the lubrication properties.
And, yes, I feel it is penny wise and pound foolish to skimp on oil changes.
A major cause of recently built cars in otherwise good condition being scrapped is low speed collisions--they do little if any damage to the body, but deploy all the airbags. At $1200-$1500 each to replace, a vehicle with six airbags could need $10,000 in repairs just to replace them.
You've gotten several answers regarding the 'technical' reasons you should change it every 6 or 12 months.
My experience -- my 5 1/2 year old Saturn just hit 30,000 miles. I've had the oil changed a total of 3, maybe 4 times. This last change was the first in probably 2 1/2 years and the mechanic had *nothing* to say about the condition of the oil, the engine, or anything else. (Well, I asked "any problems" and the answer was "no." So I guess he did say something.)
Personally, I was uncomfortable waiting that long. I think I'll be happier on an 18 or 24 month schedule myself. But, I do put 120 miles (averaging
65-70 mph) on it one-way to the airport every few months, so it's not 100% city driving.
I had a mechanic at a AAA-approved facility tell me that I was bringing the car in too often for as little as I drove it (I would have been on a once-a-year schedule at that time) so I would suggest you find a reputable mechanic and ask them.
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