RX-8 Hot start problem

Sadly, an increasingly common fault the RX8 suffers from is difficulty starting when hot. You are suffering from this problem if you find that after pulling up at a petrol station that car will not restart immediately, but performs normally after a 20 - 30 minute wait. Just to be clear this IS NOT a normal characteristic of the car. A healthy RX8, or any rotary engine for that matter, should start like any other car when hot or cold. It seems, as of late, that people are getting hot start problems confused with flooding problems. Flooding occurs when the engine is cold. I think this is something that stems from car dealers and car owners selling their cars, telling prospective buyers that it is "normal, sometimes rotaries flood themselves - leave it 5 mins and it'll start again". Flooding and hot start problems are two completely seperate issues.

Two things may be the cause of hot start problems.

  1. an engine suffering from low compression. 
  2. a slow starter motor

The only real way to determine which of these is affecting your car is by having a rotary compression test. It is important to have this test carried out by a rotary specialist, as the testing needs to be done with rotary engine specific compression testing equipment. Using conventional piston engine test equipment will produce inaccurate measurements. It is also important that this test is carried out when the engine is hot. A cold engine will produce better, but misleading results. A rotary compression test will tell you quite a few things if you know what you are looking at. When you recieve your results you should have at least seven numbers - six  of these tell you the compression reading from each face of both rotors and the 7th number will tell you the exact speed that your starter motor is cranking. According to Mazda, your results should read between 6.9kgf and 8.5kgf at 250rpm. If your results are not taken at - or very close to - 250rpm they will be standardised to this speed so as to determine the health of the engine. Cranking speed and compression are directly related. Mazda state that any rotary engine needs 180rpm to start, regardless of health. I've found this to not be completely true but it is a good indicator, so anything faster than 180rpm is good - ideally you want more than 230rpm. Just to be clear, in the same way that a slow starter motor won't start a healthy engine, a very fast starter motor (i.e. 280 + rpm) will start an unhealthy engine and so can be used to mask deeper problems.

Which brings us on to fixes. If, after you've had a compression test carried out, you find that your starter motor is slow but your engine is healthy, simply fit a faster starter motor and away you go. I have seen this scenario on several occasions so it does happen! Unfortunately however in 75% + of cases it is low compression that is the problem, not helped by a particulaly slow starter motor on older cars. In this instance you have two options:

  1. You can either fit a fast starter motor to mask the main issue but this will simply be a temporary bodge
  2. You can opt to have your engine stripped down and rebuilt with new parts giving it a new lease of life.

The first option, a new starter on a dying engine, I don't particulaly recommend as a fix. It will buy you some time if you are not ready for the expense of an engine rebuild, but ultimately the engine problems will progress to the point where it simply fails, potentially mid-journey. It is also likely that by this stage damage will have occurred to the major engine components meaning that the rebuild will be far more costly than it may otherwise have been.

The second option, although the more ideal, does require some thinking about due to the cost versus the value of the car. The first step is to find yourself a good independent RX8 specialist who will be able to talk you through the available options before you make your decision. Why independent? Mazda's policy is generally not to repair/rebuild a failed engine, but to unnecessarily fit a new engine, which is more costly than a rebuild. There are a growing number of independent RX8 specialists in the UK. Costs for the work can range from very expensive (where you may well be paying a premium simply for the company name) down to very cheap (likely with the associated corner cutting that you might expect). The mid-range specialists generally charge between £2000 and £3000. We come in at the lower end of that bracket and though it does still sound quite expensive, consider that before we actually start work, we spend £1000 on the comprehensive engine rebuild kit that assures the quality and longevity of the repair.

Hopefully that spells it out for you and clears any myths. If you have any questions or concerns regarding your own car, please do contact us and we will be pleased to assist.

Ben