Fuel Additive For Older Engines - Are They Necessary?

[Ranald]

Hi there, i would be grateful for some guidance in relation to fuel additives.

I have been told i need to add a 150ml bottle of fuel additive to every full tank of petrol in my 1985 Carina II, isn't that a bit excessive, wouldn't i get away with just addding one every couple of months?

Kind regards

Ranald

[Raistlin]

There is no magical elixir that is designed to make your engine magically become more efficient and powerful.

About the only time these additives may work is if you are not using the right octane rating fuel as your vehicle requires and you increase it to what it is supposed to be using an additive.

[MikeSh]

I had a 1986 Carina II from new for 15 years (and just shy of 250,000 miles). Just used pump petrol in it with no additives.

IIRC unleaded became more common/standard when it was a few years old and Toyota did a carburettor mod to let it run nicely on unleaded - just different needle/jet I think. (I remember the inside of the tailpipe changing from a grey to black after going unleaded - quite scary that there was that much lead in the fuel.)

Assuming yours got converted then I don't think 95 unleaded is much different now from then, so shouldn't need additives. OTOH if it didn't get modified maybe it does.

[Ranald]

Thanks for the replies, but i am still unsure as to the correct course of action though. I was under the impression that an older car without a Catalytic Converter needed to use a fuel additive to replicate the missing lead.

I am not going to be very impressed if i have to pay an extra £7 - £12 per tank of fuel, i didn't think of that when i took ownership of the vehicle, i guess i am just too used to pre 2000 living without 4 star now, it never entered my head that it couldn't run on unleaded.

[MikeSh]

Thanks for the replies, but i am still unsure as to the correct course of action though. I was under the impression that an older car without a Catalytic Converter needed to use a fuel additive to replicate the missing lead.

I am not going to be very impressed if i have to pay an extra £7 - £12 per tank of fuel, i didn't think of that when i took ownership of the vehicle, i guess i am just too used to pre 2000 living without 4 star now, it never entered my head that it couldn't run on unleaded.

Having a catalytic converter means you MUST NOT use leaded petrol - the lead contaminates the cat.

But not having a cat does not necessarily mean you must use use leaded petrol or an additive substitute (which sounds like what you are talking about).

The lead had two effects - raising the octane rating and lubricating some parts. For most cars only the former mattered, but some engines from the time of unleaded coming in need the lead for lubrication as well. Most cars (including the Carina II) did not need the lubrication (IIRC one of the Ford engines was a well known one that did) but may need a tweak (per my previous post) or an additive to allow for the slightly lower octane rating of standard unleaded.

I'd suggest you ask a Toyota dealer whether your car has been modified, in which case you have no worry. If it hasn't, then there may be three options for you:

Additives

Get it modified

Use a 'super' fuel (you'll need to check whether this would actually be OK)

Each has either a once off cost or an ongoing cost, so you'll have to work out which is cheapest given your mileages and time you expect to keep the car.