I've heard of the WD-40 starter fluid trick also. However, I believe WD-40 has recently change the formulation so the volatile component is no longer present.

Larry and jbaj700 have very good advice - do not use starting fluid! At best you might get started with ONLY a broken piston ring(s) that will cause problems and damage down the road - usually when you want it least.

Best fix is to find out why your diesel won't start or is hard to start: valves need adjustment, bad glow plugs, restricted fuel flow to the injector nozzles, bad injector nozzles, low compression, out of time IP, low/bad battery charge, bad starter or someone put a gas M-B starter in and will not turn the engine fast enough to start, clogged air filter, get a block heater, etc., etc.

Good luck!
Tom

__________________
America: Land of the Free!

1977 300D: 300,000+ miles

American Honda: Factory Trained Technician & Honor Grad.
Formerly:
Shop Foreman;
Technical Advisor to Am. Honda;
Supervisor of Maintenance largest tree care co. in US for offices in Tex.