Renault Espace starter motor won't - steve.h
I have a 1993 2.2turbo-diesel Espace with a peculiar starter motor fault. When it is very hot or after a long drive the starter motor will not turn over. If I leave the engine to cool (this may take an hour) then all will be well again. The engine itself is fine - provided I can turn it over it always starts first time.

I have swapped the starter motor and still get the same problem. I thought I had it tied down to a poor contact on the connector which goes to the starter relay (wriggling this usually allowed me to start), until last month on a very hot day when nothing worked except the "cooling-off" period. I now think it was just the act of opening the bonnet and allowing the heat to escape more rapidly which was helping.

A friend has told me that TVRs (which also have a fibre glass body) also have this problem. Has anyone else heard of this? Is this a well-known problem with Espaces, and if so is there a fix (apart from only driving in cold weather)?

Renault Espace starter motor won't - 659FBE
The problem is due to insufficient current in the solenoid winding, caused by a combination of excessive circuit resistance, and a high (hot) solenoid resistance. Many starters are marginal in this respect, and higher soak back temperatures associated with turbocharged engines, underbonnet lagging, undertrays etc. exacerbate this.

The easiest fix is to energise the starter solenoid via a relay, sourcing the solenoid current from a supply fused at about 60A and using heavy cable (at least 2 mm sq.). A 30A relay should be OK, but bear in mind that starter solenoids have a high pull-in current which reduces to a relatively low hold-in value once the main contacts close. The relay coil is of course energised via the existing wire from the key switch.

659.
Renault Espace starter motor won't - steve.h
Thanks 659. Your suggestion sounds easier than bolting on a big heatsink! I think I'll put the starter in an oven and do a few measurements to work out how big the relay and fuse should be.

My point about TVRs maybe suffering from the same problem was that the metal-body in a "normal" car might help dissipate the heat (fibre-glass is a better insulator). But you're right in pointing out that the pattern of airflow around the engine compartment is probably the most important thing, otherwise every fibre-glass car would be sat on the roadside in hot weather!

Cheers. Steve.
Renault Espace starter motor won't - 659FBE
Steve, if you want to replicate this problem, you will have to include the solenoid circuit resistances, particularly that of the starter key switch and its wiring and connectors. This is not too easy to do on a "domestic" basis, but I have tested many of these in the past in the course of my work. Bear in mind starter soak back temperatures can approach 200 deg C.

Apart from heat soak problems mentioned, any vehicle with long cables in the starter solenoid circuit or lots of connectors will be prone to trouble (I had a SAAB with the ignition switch between the seats which had this problem, but SAAB at least had the sense to increase the cable sizes on the next vehicle I had from them, which gave no trouble).

I seem to recall that the most unfavourable combination I tested was a Bosch starter and a Valeo keyswitch, the latter tending to develop high contact resistance with ageing. The starter was just too marginal in terms of the hot engagement force available from the solenoid when the drive was dirty and under conditions of tooth-to-tooth engagement, when a lost motion spring has to be compressed. In any event, a relay is a cheap fix.

659.

Renault Espace starter motor won't - vmturbo

Sounds awful but one cheap improvement is to replace the steel nuts on the starter terminals with brass ones. I have neticed a huge variation in the price of Espace starter motors from the same firm, Bolk (Chinese?) seem to be the cheapest whilst Bosch are the dearest at about five times the price of the cheap ones.

What I do know is that the cheap starter motors on the engines used to power 5KW generators normally have moulded commutators (the copper segments are just stuck into plastic) Prolonged cranking can cause the segments to become unstuck!)

Heavy duty commutators are made like wedges of cheese and they are held in place with dovetails.

Most vehicles have a Canadian option, this is a battery with 50% more capacity and a heavy duty starter.

Note that the design of most starter motors is illogical and the same goes for alternators. The problem is how they are earthed. Usually earthing is done at the drive end hence the current has to travel down thin screws or via very dubious connections between the "pot" and the end flanges. This is in fact a common failure on the starters of some well known American motorcycles. In this case the cure is to run a heavy earth braid from one of the starter motor mounting bolts and bond this to the end cap.

Some modern alternators now have an earthing point on the end cap. This is far better than relying on numerous fortuitous joints which may rust. In the case of my Ford Granada 2.8 there were about a dozen fortuilous joints between alternator B- and battery B- and in the damp climate some had rusted. A yard of earth braid transformed the car!

Getting back to the Espace, the starters have a steady bracket at the terminal end. It could well be that when the engine block is very hot and expands, this bracket tries to pull the starter apart and causes bad fortuitous connections (the ones between the end flanges and the central "pot") As to the resistance of the starter solenoid coil, if it was 50 ohms at 20 degrees C it would be about 65 ohms at 100 degrees C and I just cannot believe that this modest increase in rsistance is the cause of the malfunction. Good luck!

 

Ask Honest John

Value my car