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Why is my car so slow when it's hot?


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Any ideas? Been hot down here pretty much every day for the last couple of weeks, and it's been running a bit rougher and a lot slower. Drove back from `No-Rice` last night and it was 16 degrees instead of the usual `25-27` degrees - it was like I had an extra 50bhp!

Any ideas? I know it'll go slightly slower in the hot weather, but not this much...

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Tyres are all inflated correctly - anyway, higher temperatures makes the air expand so they'd be overinflated - better acceleration, less grip.

Aircon does make a noticable difference, but it's slow even with it off - with it on it's really slow smile.gif style="vertical-align:middle" emoid=":)" border="0" alt="smile.gif" />

I'll check the coolant level tonight. Any other ideas?

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Any car will run better when there is cold air running through the engine, so when the air cools down in the evening or the day is colder then the car will run better and feel that bit quicker.

My car feels like its flying in the autumn/winter, best time for a thrash is dusk in the summer as air is normally cooler.

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If I take my intake cover off so it's taking in hot air from the engine it feels like you've lost about 50bhp, sounds like a tvr though laugh.gif style="vertical-align:middle" emoid=":lol:" border="0" alt="laugh.gif" /> could be a cracked breather pipe or something like that or the cover for the airbox could be loose.

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Ok heres the science!

I wondered this last month: " where is the coldest air in my engine?"

So I went out and bought a fridge thermometer, the ones chefs use on their fridges, it has a digital display and has about 3m of wire with the thermocouple on the end! (£3 ish)

Placed it next to where the air hits the induction kit. When engine warm and traveling at a steady 60mph, temp was around 25oC.

When stood in traffic lights, temp rose to 56oC.

Moved the thermocouple (end bit to the layman) to different areas in the engine, and also under the front bumper, grille, etc. (havent done anything drastic like remove a lamp.....yet), had varying results. All this was to find out where the coolest air is, as the colder the air is the more dense it is and therefore the more combustion takes place = perfomance!!!

So I should imagine that the warmer the outside air temperature is, the less dense the air is = less combustion. :roll:

Hope this helps. smile.gif style="vertical-align:middle" emoid=":)" border="0" alt="smile.gif" />

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  • 1 month later...

Ive got a pipercross ind. kit on the arosa, tried it without a cold feed and it makes the car feel much slower than standard on a hot day (fine when its cold and the engine hasnt run for long), now ive got a cold air feed from the front grille blowing straight into the filter it makes a huge difference.

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