[pidim]

Hi everyone,

In the last few days I have noticed my car does not increase RPMs on a cold start, but seems to start and rev only slightly higher than regular idle compared to the past.

I have normally been running regular 91 petrol, but I have noticed this ever since filling up with BP Ultimate 98 (for the 1st time).  Would the engine change the way it starts based on octane and not need the higher RPM on cold start? I have used 95 octane on several occasions and there was no difference, but never used 98, so I'm wondering whether this would be the reason.

I hope my explanation makes sense and if anyone can contribute more to my understanding.

[Phil №❶]

Not sure. The difference in petrol is most likely detected by the ECU for ignition timing purposes, but in a cold engine, there are many other sensors that assist the engine to warm up quickly. The ambient temperature of the air, coolant temp and air pressure and moisture content are all factors that could alter the starting pattern. A warm engine is a more efficient engine, so the only real way to test your theory, would be to return to the 95 and see if there's any difference.

[pidim]

Thanks for that. Hopefully nothing starting to go wrong.. Will advise

[Dazzler]

Is driving response normal when cold? If so, I wouldn't be too concerned..

[pidim]

hi, yes all driving response is normal apart from the low rev startup.

[Dazzler]

 

[Asterix]

As long as the idle is slightly higher than normal I wouldn't be too concerned.

I had a similar problem with the wife's 1996 Corolla, but it wouldn't do any higher rpm's when cold compared to warm, and that's a problem when having -10ºC. 

Engine coolant temp sensor replaced and then cold idle was at 1200rpm. 

[pidim]

Hi again everyone, thanks for your feedback.  I thought I would report back just as a FYI.  After letting the 98 fuel BP Ultimate run down to almost empty, I filled up with 91 Fuel after work and drove over 30km.

 I started the car this morning and RPM's were back to where they used to be on a cold start.  It seems from this, that Octane levels certainly influence how all the sensors etc react to a cold start and obviously with the extra octane, the engine can cope far easier on cold starts without having to increase RPMs.  Well anyway, that's my take on it.

[Phil №❶]

Higher octane fuel burns slower than lower octane, so the power is more evenly produced on the power stroke. Too high octane fuel (as in racing fuel), can result in the fuel still burning on the exhaust stroke which doesn't do the exhaust valves a lot of good. Anything bought from the servo's would be ok for your car.

Thanks for the feedback.

[Dazzler]

 

I might have to try some 98 in my new car! 

[eye30]

I understand here, UK, they alter the fuel content, not sure what they do, for each season.

With diesel this is especially important to prevent clogging in the colder weather.

[pidim]

Higher octane fuel burns slower than lower octane, so the power is more evenly produced on the power stroke. Too high octane fuel (as in racing fuel), can result in the fuel still burning on the exhaust stroke which doesn't do the exhaust valves a lot of good. Anything bought from the servo's would be ok for your car.

Thanks for the feedback.

Would you recommend not to run 98 if a car like i30 is spec'd to run on 91?

[Phil №❶]

As I said, any fuel you can buy commercially from a service station would be suitable for your car. The members he are quite divided when it comes to 91 or 98. Some say that 98 is more economical and cleaner burning, even though it's dearer to buy. Others report no problems at all using 91 continuously. If the car is ok on 91, then that's what I would use.

[pidim]

Thanks.  Personally I have not noticed any difference in fuel use from 91,95 or 98 - so I'll stick to 91 for the time being

[Phil №❶]