Maninder

So I have a 2005 Mazda RX8 Automatic
KM: 103,800
New Engine: 25000-30000km

I know the coolant light comes on and stays on after driving it for a while and on a summer day like today the fan kept running while the car was in on mode, just before starting.

My car had a hard time starting when it was hot I know everyone is going to say its a compression issue, but does the faulty coolant sensor light being on have any effect on the car starting?

RIWWP

iTrader: (2)

Um no. Why would it?

The light is just part of a simple electrical circuit which closes when the coolant level float drops too low, connecting the circuit's power and turning on the light.

blckninja

iTrader: (1)

Also doesn't have to be compression issue, could be spark plug. Some 8s have been known to have hot start issues in which case you would want to get the proper plug.

Don't know too much about this topic, just know it's an issue.

RIWWP

iTrader: (2)

^ incorrect

^ correct

blckninja

iTrader: (1)

I thought that some 8s had hot start issues due to spark plugs? Guess i'll nevermind that one and look inti it more, must have misread something. :|

RIWWP

iTrader: (2)

The only reason to ever use a different plug is if you are turbocharged or supercharged.

Basically there are 2 factors of importance to get the engine started: Compression and Ignition.

The stronger your ignition, the easier time you will have firing a mixture at a given compression rate. So for any given ignition health, the higher the compression the easier it will be to fire the mixture. (this is all at starting and within this engine, other engines and other times, this isn't all true)

So getting that compression needed is important. Think about it as a threshhold. You need to surpass the threshhold to get it to fire. Under the threshhold and it won't. Compression is affected by the state of the seals, the temperature of the engine metal, and the crank speed of the engine. Crank speed of the engine is affected by the health of the starter and the available battery charge. So essentially 4 different factors affecting engine compression when starting.
1 - Seal condition (worn seals = lower compression because it can't seal well)
2 - Temperature of engine metal (hotter = lower compression because the housings expand away from the rotors and the seals have a harder time filling the gap)
3 - Available battery charge (lower = slower crank speed = lower compression)
4 - Starter health (lower RPM from age = slower crank speed = lower compression)

You can compensate for one by improving any of the other ones, and as long as you get 'enough' compression for your ignition, it will fire.

Since the starter, battery, seals, and ignition are all basically the same starting cold as when starting hot, hot start problems that don't exist when cold means that the hot engine expansion is greater than the seals can't handle, resulting in insufficient compression to start correctly.