s3 hot starting problem

[driver]

Hi Rob Gill here,
My s3 seems to be developing hot starting problems,like it struggles to turnover when engine is hot,but once engine is cold it start ok.I have also noticed engine temperature gauge runs at 3/4 the car has new radiator header tank and hoses ,could this be an opus ignition system problem ?

[jagwit]

Get rid of that OPUS rubbish ASAP!!! Easiest / cheapest?? is to find the "double coil" ignition system from an XJ12 or Daimler double six but there are other choices out there as well. My E is running well on Lumenition all the way to 6000rpm. (Running a V12 at 6000rpm requires a very competent ignition system due to the short amout of time available to charge the coil(s) ). By using the DD6 dissy etc, you will also get the benefit of having vacuum advance on your car - which could yield substantial fuel savings (>20%) and the car will feel perkier at part throttle.

As for the difficult hot starts, please read this thread: Hot start issues

[jagwit]

I have also noticed engine temperature gauge runs at 3/4 the car has new radiator header tank and hoses

There are two other very relevant cooling issues pertaining to the V12:
1) quite often the bypass valve on the thermostats (that flat disc at the end of the thermostat) don't close the bypass circuit completely. This results in coolant not making its way to the radiator. The reason for this is that many thermostats don't move far enough to close off that port. I found and corrected this problem on my E (having read about this issue on jag-lovers) by bolting a 3mm disc to the bypass valve disco on the thermostats in my car. Pic below.

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2) Most of the coolant being pumped into the block simply pops out into the head at cylinders 1 & 2. This is due to the head coolant ports on the thermostat housing being too large, making it too easy for coolant to flow out the block and head right at the front of the engine. I implemented a version of the "Lutz mod" on my car which has also cured the "coolant dumping" issue. I installed washers (6mm hole) to the thermostat housing ports which now force more coolant to the rear of the engine. Coolant dumping problem solved.

tn_20170707_100447.jpg (91.22 KiB) Viewed 4607 times

[SRK]

I recently went to the SNG Barratt ignition system and it does make a significant difference in starting, both hot and cold. (particularly when hot) If your having a cranking issue then I would look to the cooling system but if its cranking fine and just not firing when hot its probably the ignition. The Barratt system was something like $650 after the core charge (which they returned very quickly) and took about 5 hours to install. (would have been a little shorter but I didn't get the distributor right the first time) The instructions are very good.

Steve

[lundabo]

Seems like a fuel issue. Opus failure for me was shut down while hot, not hard to start when hot. Has anyone else experienced hard hot starts related to Opus?

[MarekH]

Dear Bill,

That sounds about right to me aswell. There is quite a lot of latitude in when and how much spark you give it to make it fire. There is plenty of scope for atomised fuel to condense out on the internal surfaces of the manifolds before it even reaches the cylinders and that assumes you drew enough air across the needle to atomise any in the first few seconds of cranking anyway.

Fuel injected cars solve this by siting the injector right above the inlet valve and precisely metering the amount of fuel dependent on temperature. It isn't a surprise that they all start so much more easily than a carburettored car.

In any case, if you were to replace any heat and time expired components inside the OPUS and overhual the distributor, you'd have a fair comparison being made against the reconditioned distributor sold by SNGB and few more spare dollars in your pocket.

kind regards
Marek