DeTomaso Mailing List: September 2000, Message #13

Well, I'm at the end of my rope for the moment... I need some more rope.

Yes, the 351C in the new Mach I engine is overheating, according to the
guage in the dash.

Background:
The original engine I had rebuilt 15 years ago was build with dished
pistons, open chamber heads and a mild cam.  The temp gauge ran about
one-third into the "normal" range.  All was one with the universe.

The new engine is built with flat top pistons, quench heads and a radical cam.
I'm running about 10 degrees of initial advance, at idle.  I'm not sure how
the carb is jetted, I just know it's running (it might be too lean).

When running for less than five minutes, the temp gauge is almost pegged on
High , past the "normal" operating range.  However, there does not appear
to be coolant ejecting itself, and when shut off, there are no audible
indications of bubbles.  The upper radiator hose feels cool.

Okay, so I go down and pick up two things from Napa, another thermostat and
another temp gauge sending unit.  I go home, I extract both from the
engine.  I go into the house and using a "non-cooking" pan, I insert both
thermostats (old and new) into the water and start it boiling.  With a
thermometer in the water, I find both thermostats begin opening at about
200 degrees as read on the thermometer.  The 'stats are rated at 195.
Seems to me they are opening a bit too late.  Anyway... both are the same,
must be okay.

I do the same with the sending units.  I boil them both for a good amount
of time, then extract one and take a resistance measurement.  It starts at
about 35 ohms and slowly climbs to about 45 to 50 as it cools.  The more it
cools, the higher it gets of course.  I then extract the other one and it
reads about the same, starts around 35 and begins climbing at about the
same rate.

Argh,  This indicates to me that both sending units are working, though
they BOTH may be the wrong range.

Okay, this next part is confusing and needs some accurate interpretation,
so I'll try to accurately relay the symptoms.  Please bear with me.

I install the new 'stat and the new sender (why not).  I then fill the
radiator with the same fluid I drained earlier.  Due to what are probably
air pockets in the system, I can't get quite all of it in.  I put the cap
on.  I start it up.  Stupid me, left the temp sending unit wire unplugged,
so while the car looked okay, I went about putting tools away and cleaning
up.  Less than five minutes later (or less) I notice a waterfall coming
from my overflow tube, what the hell?  Here is the important part, I feel
the upper radiator hose... it's cold, but under a lot of pressure.  The
fluid overflowing is luke warm, actually cool to the touch.  What the hell?
 I shut it down and hear gurgles and bubbles and all kinds of noises for a
few seconds, then it all gets quiet.  I try to slowly remove the radiator
cap, it's cold, at the first step it starts blowing cold radiator fluid all
over so I tighten it back down.

I start the car again and let it go.  The overflow has stopped, I continue
to monitor the upper radiator hose, which I can now squeeze flat by hand.
I must have vented enough pressure, but where the hell did the pressure
come from.  Do I have a compression leak into the water jacket?  The engine
continues to run, it starts getting hotter, I notice the wire hanging that
should be connected to the sending unit, I attach it, and check the gauge.
The temp gauge reads past two-thirds in the normal range and is still
climbing.  I continue feeling the upper hose, it starts to get warm but I
can still squeeze it almost flat by hand and I don't seem to feel any fluid
flow.  The radiator is still pretty cool except for one spot about the
middle which is starting to get pretty warm to the touch. (yes, the
radiator is fine, I flushed it thoroughly before installing and it flowed
very well).  Still no steam or any more fluid out the overflow.

I check the gauge, it's reading slightly over the top of the normal range,
just one neede-width away from the "H" mark. (limit of travel for the
gauge).  The upper hose is very hot but I can still squeeze it and it
doesn't seem as though it's flowing, at least I can't seem to feel anything
going through it.

So I grab a thermocouple probe I brought home from work. I place it next to
the temp sending unit on the front of the engine, just under the thermostat
housing.  it reads less than 190 as I hold it there for quite a while.
That tells me it's NOT overheating.  Okay, what the **ck over.

Soooo........ any ideas?

- Why did the radiator overflow cold fluid?  Was it air pockets in the
block expanding under the pressure of warming up? and forcing fluid back
through the water pump inlet?  Until the thermostat warmed enough to open
and equalize the pressure? (no, I forgot to drill a small hole in the stat
to help bleed air, DOH!)

- Why does my gauge read too high?  Is it really too high?  Doesn't jive
with thermocouple reading taken by hand.  Would both brand new temp senders
from Napa be wrong?  I sat with thier rep and made darn sure I had the
correct one.  Could the factory be packaging the wrong ones?

- Why was I able to squeeze the upper hose when warm, is that normal?
Shouldn't it get harder to squeeze or at least shouldn't I feel fluid flow?

-  Could it be my gauge has gone south?  The instrument voltage regulator
might be a culprit, but all the other regulated gauges read okay, so I
don't think that's it.  The gauges though haven't been used for three
years, could it have developed corrosion?  Would throw the reading off?
Corrosion = increased resistance, increased resistance = lower temperature,
therefore corrosion = lower temp reading on gauge.  I guess that doesn't
make sense then.

Ack... I'm all confused, I need a tech session with the experts.  I've lost
my confidence in troubleshooting this thing.  I also don't have confidence
in driving the car if it is indeed overheating.  I'd hate to ruin this
brand new engine.

<sulking off his soapbox>
Asa Jay
: (