It's not real bad, but this time of year all those small problems which
one normally lives with suddenly become major concerns which of course
are about to cause an engine explosion, probably on a critical run on
the North course. Perhaps someone out there has had a similar experience
and can offer hints on what to worry about.
Engine is 1558 Lotus twincam, circa 1967. Bottom-end rebuild last year,
top end the year before. Stock just about everywhere, including dual
Webers, radiator, water pump, oil pump, etc. Exhaust is update to Sprint
headers, also factory. Stock radiator and fan (not much room for elec-
tric fan on this one, later ones came stock with them, we may update).
Basically same configuration we've run for years in terms of jets,
chokes, etc., and timing advance. It has an Accusump.
Symptom: when first started at an event, the water temperature gauge
indicates that the engine is taking its normal length of time to warm
up to desired operating temperature (180-190F). Oil pressure is good
(50 lb at idle, drops to about 35-40 when it gets warm), no bad noises,
car sounds great. After a couple of runs (autocross), however, the
temperature goes up rapidly after coming off the course. We'll start
a run at 190, hit the exit lane at 180, and by the time we idle back
to grid we're passing 210. Oil pressure still okay (30), still no bad
noises, just this temperature thing. And no, I don't think it's the
gauge--the engine radiates lots of heat when this happens. If we
get out the sprayer and water down the radiator it will cool fairly
quickly. But next run it will do the same thing. It's worse on hot
days than cool, but it still does it somewhat even when we're wearing
sweatshirts or jackets. Yes, we checked the coolant level and there's
plenty. Yes, the water pump was redone recently too.
The only significant change we've made lately is to install an MSD not
too long ago. I've heard conflicting reports of MSD's causing higher
operating temperatures (or not), so perhaps it's something to do
with how hard we crank the engine on-course (lots of time spent
between 5000 and 7000 rpm, rev limiter hits at 7000) and the fact
that once we come off it's just idling and the pitiful stock fan
can't move enough air across the radiator at low R's to get it
cool. But if that's the case, why doesn't it start to do this
until after a couple of runs? If it's hot, it should run hot at
idle while we're putting it in grid the first time, right? I'm new
to this MSD stuff, so perhaps there's something I'm missing which is
perfectly obvious to the initiated.
Anyway, that's the extent of our paranoia at this time. Anybody
had an experience at all similar? And on a related tack, what's
the hottest it can get without doing itself harm (aluminum head
on iron block)? 230? More? Less? It never stays hot for more
than a few minutes, but I'm not sure whether that matters much.
Karen
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