Fuel additive

[Nigelblandin]

Evening all, I run my ‘85 GTL on Tesco 98e5 fuel which is pretty much zero ethanol from what I understand. The previous owner added Redex additive for the lead replacement, is this still needed?
What’s the current thinking?

 

[malcolm]

The lead replacement is different from the `octane rating. Petrol has zero lead these days. Also the R4 will run fine on the lowest grade of petrol.

If you are just running the car around as normal there shouldn't be any need for an additive to replace lead. These cars have valve inserts that ought to be tough enough to run without it.

If however you are contemplating a motorway road trip at full speed for maybe 3000 miles you'll likely burn a valve. High grade petrol and a lead additive would probably help - it's because the R4 was set up to run a bit lean full out and modern petrol especially with ethanol tends to make it even more lean so things can get hot in there. Aged distributors can make it even worse. It's not a bad idea to remove the main jet and push a 1mm drill bit through it by hand and maybe pliers (and not using an electric drill). That cleans up residue inside the jet and a helps avoid a lean mixture that might result in valve damage. Stop if you see any bits of jet coloured metal coming out.

There is the consideration about how much ethanol you want in your tank if the car is going to be sitting for a long time. Ethanol absorbs water and on modern cars it's not a problem. On those the tank is sealed for emissions and the water can't get in. Renault 4 tank is not so well sealed and the water can rust the tank from the inside. Over time this can rust the tank out from the inside and you can't buy GTL tanks any more.

 

[Nigelblandin]

Thanks Malcom.
I’m doing a fair few miles ( enjoying Claude so much!) but avoiding motorways( boring) if I can.
I had wondered if they had hardened seats in ‘85.

I think I’ll stick to the 98 to avoid the ethanol and as a 4 doesn’t drink like a Range Rover , hang the cost, and forget the Redex.
It’s running really well, but I swear I heard a little pinking yesterday so I’ll retard it a tad, currently at 7 degrees.
CO is at 1.5-1.6% so not too lean.

 

[André4Renaults]

In my opinion the CO level you quote is too low. I believe the correct volume is about 3-4% and too lean mixture can cause burnt valves, regardless of the lead content. Before altering the ignition timing I'd enriched the mixture a tad and see how the car runs then.

Do bear in mind that, although a "lean" CO setting may assist fuel economy, the cost, in burnt valves etc. is car more! Perhaps check the workshop manual for the correct CO setting, but I expect you'll find it to be around 3-4%

 

[Jnr-Renospeed]

I always use E5 Super petrol, Esso seems to please my Cleon engine. If the car is sitting un-used for some time, use some ethanol protection additive such as Millers VSPE.

Drilling out the main jet to 1mm is a good idea like Malcolm says, then adjust the carb accordingly. You'll win back some performance from where the carb has aged.

And honestly I wouldn't worry about the CO level being at factory, these Zenith carbs are all worn to some extent by now and you'll never get the car running to perfect new factory level. Get the carb to as best tune for performance and idling then just lean off the mixture when it gets an MOT . And give the car a hard blast up in the revs occasionally just to de-gunk everything.

 

[Nigelblandin]

Good points, well made. Thanks- I will fettle and see how it goes.

 

[Nigelblandin]

So, Following your suggestions, I went back to the old way and set the mixture by ear, road tested it and then checked the numbers.
I’d stripped and rebuilt the carb last month, so knew that was ok.
Now it has more, smoother oomph, no sign of pinking and still starts and runs really sweetly.
CO is now at 3.4%, I left the timing as is (7 deg) .
Thanks chaps, Claude is really motoring now….l may need some Gordini stickers!

 

[malcolm]

The mixture screw is an idle mixture control screw but it does influence low speed running too. It's handy to have something we can twiddle to get past the MOT and then set it back how we like it. Set that for best driveability.

Valves don't tend to get damaged during low speed running. I've only managed to destroy valves through sustained high speed running on motorways. The theory behind that is interesting. Any non-optimal fuel mixture tends to burn slower than the optimal mixture. For example if the mixture at speed (which is controlled by the main jet) is too lean you would need to advance the timing to give the fuel a little more time to burn so that the car runs properly. That makes things too hot and would lead to burned valves if you were to do 1000 miles flat out on a motorway. A valve additive would probably help a little in that case but wouldn't solve the problem. Doesn't mean it isn't sensible to put some in before long motorway trips.

I've had valve problems in the past but my days of high speed driving in the Renault 4 are probably over. When you are bumbling around like I do these days I would guess there is no risk at all of valve damage and I don't put anything in the fuel. I try to set all the distributor and carburettor things up so the car is running nicely.

 

[angel]

Note that you can't measure CO value at full load on an MOT gas analyser, this one measures idle CO or low load CO value. Ideally, you need an AFR meter and check the reading on the highway.
Malcolm, you couldn't be more right! Ethanol added to modern petrol makes the "known" stoichiometric value (14.7:1) too lean in practice since ethanol has lower thermal efficiency than petrol.

 

[Nigelblandin]

Since last writing, I’ve kept the mixture and knocked the timing back a degree or so. Absolutely spot on for me now.
I love relearning all of this. Starting with the book numbers and finding the sweet spot due to age and fuel variables and, of course, the accumulated knowledge of this forum!
Thanks all.