So I know that we have had numerous discussions about this, but don’t remember this specific question:

What would happen if you put diesel in a petrol car then drove, compared to what would happen if you put petrol in a diesel?

Is one worse than the other?

Think petrol in diesel is worse,petrol perishes rubber seals etc

I saw a similar question on Honest John the other day. Apparently you can get away with it if you only put a small amount in, i.e. less than 10 litres. Or something. Read the article, don’t take my word for it

Diesel would kill the cat on a petrol car. Which is bad.
Petrol in a diesel car in small doses is OK. IMO .15 litres, just brim the tank with diesel. Cat not important for MOT on a diesel – it’s only there to placate the hippies.

Caveat – Bangernomics only. If you can afford a new car, you can afford the £200-odd cost of draining the tank.

Diesel would kill the cat on a petrol car. Which is bad.
Petrol in a diesel car in small doses is OK. IMO .15 litres, just brim the tank with diesel. Cat not important for MOT on a diesel – it’s only there to placate the hippies.

Wrong way around AFAIK

When I put petrol in my wifes’ diesel (probably 30l petrol vs 30l diesel) I had the RAC drain it, and then put it (diluted) in my petrol car. Both been fine since.

Modern diesels rely on the lubrication qualities of diesel to keep all the components running, without that they are pretty much knackered?

There are an absolute boat load of other reasons too…….

Caveat – Bangernomics only. If you can afford a new car, you can afford the £200-odd cost of draining the tank.

Modern diesels rely on the lubrication qualities of diesel to keep all the components running, without that they are pretty much knackered?

plenty of common rail engines will fall into the bangernomics category now

Diesel in a petrol is bad. That is why the diesel pumps don’t fit into petrol, where as the opposite won’t work (unless you have a fancy car).

A small amount of petrol in a diesel is usually OK. Dilute it and keep filling it up after it drops to half for a while as the petrol sits on top of diesel in the tank.

Petrol as a spirit has no lubricating properties so will knacker up a Diesel engine. Diesel as a difficult to burn heavy oil may coat components causing issues; spark plugs and cats etc. neither ideal, I’d say an excessive amount of diesel in petrol being worse. (‘Excessive’ ratio dependent on the specific engine, some are more forgiving than others)

I read all this stuff about diesel getting better MPG than petrol, so put some into our car last week – seems OK so far, but no real MpG difference to speak of yet..

DrP

Just repaired a miss fueled 11plate passat diesel. Complete fuel system contaminated with the swarf of the disintegrated high pressure pump, final bill was in region of £4500. Compare this to my old 2000 passat and my old pug106 both diesel ran both on the waste fuel drained from miss fueled tanks, passat wad ran 3:1 ratio 3 being good diesel but the pug was 2:1 2 being cooking oil smelt like a bbq but at equivalent to about 70/80 pence per litre who cared, it ran smoother and cleaner with better economy

Diesel in a petrol is bad. That is why the diesel pumps don’t fit into petrol

I thought that stemmed from leaded vs unleaded

My first Saturday job when I was at school was as a pump attendant at a very busy fuel station. This was around 84-85. I once asked a wagon driver why he had just put a gallon of petrol in his diesel tank. “To stop it freezing” was his answer.

I am assuming that one gallon in an HGV’s fuel tank was such a small percentage to not affect it. I also assume that modern diesel now has additives to prevent this.