Synthetic oil in old motors ??

Why would you want to change to synthetic ? It costs more.

Yes i have been told the same. I wouldn't risk it in my GQ.

I have thought about it too, but I find the theory about carbon all wrong?
If you have too much carbon build up around the rings, your rings seize and then crack and new motor coming up.
I am talking from experience here, the previous owners of my 2H never had injectors done in 400,000 and the same result happened.
I would be glad to have the carbon levels kept low, at 80,000 i would think it would be a good time to keep the old girl cleaned out.

Cheers Pesty

Years ago whilst studying hydraulics at the tafe the wise old teacher told the class about viscosity index and he said the ubeaut synthetic oil was to thin for the greater clearances in the old engines. Modern engines are machined to much closer tolerances he said.Old ford engines like clevelands start out with lubrication problems at high revs and so the boy racers have to restrict oil flows to some parts of the motor in order to lube the rest.What the teacher said made sense so i would not put synthetic in a motor pre 1990. Steve

Viscosity... Hmmm.
Mobil 1, just as an example, is rated at 5w-50. (I'm not recommending Mobil1 in a diesel, though I use it in ALL our petrol engines including generator, mower, and three cars.)
ie: when cold it has a viscosity of 5.
When very hot, it's viscosity is 50. Best of both worlds.
Brian-
Basically synthetic is much better than mineral oil in EVERY single respect .... no if's or but's......except price.
Especially in the case of Bypass filtering to allow extended oil changes, I fail to see how it could not be a good thing. (I have been using bypass filtering on diesels and petrol engines for about 37 years with nothing other than outstanding results...and dramatically extended oil changes.)
I will definitely be changing to synthetic on my GQ Diesel soon (when I run out of the last mineral oil I have- in a 200 litre drum.)
Also, if removing that carbon around the rings etc DOES happen- what about the special and expensive flushing oils that some people use. (Don't they advertise on this site??)
I thought carbon build up in engines was bad news....
As I said, I WILL be changing to synthetic soon.
Cheers

Hi Brian, based on my personal experience i wouldn't hesitate to switch your cruiser to full synthetic.
I use Mobil 1 (5W50) in every fourstroke we have from the Briggs and Stratton lawnmower, Robin 3.5 KVA generator, all the family cars (EFI petrol), motorcycles, Hilux Surf (1KZ-TE) and our Hino RB145 motorhome (W04CT 3.9L turbo diesel).

While some applications have been from new (after run - in) - there are a few, bought second hand, that have had reasonable high mileage when switched to synthetic.

The only vehicle that started using oil was a 1990 Ford F150 4x4 (5.8L EFI windsor engine) with around 130,000K on the clock. At the first oil change after purchase it was put on synthetic. On a trip soon after it was using oil at about 1L/1000K - which i considered excessive although is in manufacturers specification. This oil consumption continued for about 3000K and then it started improving. Eventually on a trip from Cairns to Darwin and return it didn't use virtully any. I suspect that the oil control rings were probably gummed up when we bought the vehicle and that the detergent action of the synthetic had cleaned them up so that they started working correctly.

We did a oil sampling/analysis exercise with the Hilux Surf. Toyota recomended oil service interval is 5000K (oli and filter) and the first synthetic was analysed at this change. Mobil recomended extending the next change to at least 7500K, which was done and analysis done again. Still good. The service interval was then extended to 10000K (double the toyota recomendation based on mineral oil) and analysed again. Still OK!. So the next change was run out to a 15000K interval. At 15000 K the synthetic oil still had better viscosity index than NEW mineral oil! The ash levels were starting to come up, which could have been kept low if i had fitted an additional bypass filter. We decided at that stage to try for 20000K the next time - and believe it or not the Mobil analysis came back that despite the raised ash levels, the oil was still good. Since then we have standardised on 15000K (three times the Toyota recomendation) and oil consumption has always been zilch!
When costed out - it means that although the synthetic is more expensive initially, because we have trippled our interval - then overall it is cheaper because we are only changing one filter instead of three, and the oil is lasting three times longer.
The other benefits of much better start up lubrication, low and high temp lubrication, and improved fuel consumption are all a BONUS!

Carefull monitoring of fuel consumption on all vehicles has shown an improvement between 8% and 11% on all.
As an example a Yamaha TT600 with a 20L acerbis tank would normally run the main tank out within 5K either side of 300K. Then needed to switch to reserve. After swinging it to Mobil 1 - the 300K average immediately became 330K before running the main tank out. 30K is a long way to push a motorcycle!
I have used synthetic in Honda XR's and Yamaha TT's without problem, but know some who have had sliping clutch issues in some bikes with wet clutches. Mind you ANY friction modified mineral oil WILL cause clutch problems and motorcycle manufacturers usually have specifically recomended oils to use. Mobil do make a full synthetic motorcycle oil - however i havent had the need for it -YET!

Go for it Brian - irrespective of brand - FULL synthetic is the way to go. Don't get the 'synthetic modified' or 'synthetic fortified' mixed up with FULL synthetic.

Tuco

I appreciate ALL answers to my original query , however when examples or "test cases " are presented it is more convincing . So on that theory the " yes " case has a nose in front !!
Thanks again fellas

I'd advice you against using synthetic oil in your cruiser. My experience in the past has been that the more efficient cleaning properties of synthetic oils can cause an older engine to leek like a sieve from gaskets and seals by removing the builtup of sludge. In your case I'd say, with an bypass filter installed to keep the engine cleaner, synthetic oil would be an unnecessary risk.
Just my two bobs worth.
Have a nice day!
Cruiserman

G/day Brian, mate the synthetic component in the oil has nothing, I repeat nothing to do with the detergent action... it is simply an anti friction additive... nothing more, nothing less... basically you will achieve very little by changing over to it with your donk at 80.000 Ks, your friends son is pretty well on the money,. Stick to regular maintenance with a good quality diesel oil which I might add, has a higher detergent rating than any petrol eng oil… plus it’s a lot cheaper.
Cheers Ron.

I don't advise synthetic oil for a old 12ht. Recommend regular oil change @ 5000klm with a quality name brand 15/40 diesel eng oil.Why ? it is cheaper there is really no difference in ware it is just market hype. unless you drive a very performance orientated eng (eg racing application) you will only giving more money to somebody that is really not deserving of it. Mineral oil is fine if you do your service regally. OK it takes about 9 ltrs of oil by memory. You can buy a very good oil for $36.00 for 10 ltr a oil filter say $10.00 ok oil change is going to cost you $56.00 & a couple of stubbies....now lets look at synthetic lets just say you go on another post here ...you get 7500klm between service the oil costs $180.00 for the oil the filter $10.00 & you still need a couple of stubbies ..you do the maths mineral oil comes out on top .Yes synthetic oil is great for hi performance engines operating under extreme load but it is really not needed in a common light duty diesel.
As for a decrease in fuel consumption i am sceptical.
I have seen identical engines (cummins big cams) with similar hrs on each one using syn oil the other using min oil the internal ware was not really any different on either. Market hype has a lot to answer for.
Please your self & don't forget that the 12ht was designed to use mineral oil with a 15/40 rating for normal temperature areas ..hope this helps ...666toy