Chasing ghosts Temp spikes on 300m

After pulling the left head (to retrieve a broken spark plug electrode)
and getting the engine back together, the car runs great - except the
cooling system has lost efficiency.
Previously the temp gauge stayed a bit below half mark. Now it stays a
bit ABOVE the half mark and after driving uphill it spikes to near red.
The usual stuff has been done: new upper/lower hoses, tstat, radiator
been rodded out, timing belt replaced (thought I heard it slipping on
the water pump pulley), pressure cap replaced, system has been bled.
No apparent leaks internal or external.
Normally I would replace the water pump but it only has 50k on it and I
feel like I've been chasing ghosts so far.
The only things left are the water pump and the big question - could
something be blocking a water passage in the head that was removed?
These seem unlikely becasue the pump circulates very well to the heater
(which brings down the temp) and if a water passage was blocked it
would heat up at idel (which it does not).
Any thoughts?
My next move is to try an OBD reader and see if ther is something
happening with other systems that kick in on the uphill climbs (vaccum,
timing, fuel).

 

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Allot of typing but I see no year/engine size?

Glenn Beasley
Chrysler Tech

 

Ah, yes. '99 300m with a 3.5
I was hoping someone else had run into this temp spike under load
scenario.
Other symptom: when it gets hot, reving the engine to 2000 rpm for a
minute brings down the temp

exotic diagnostic tools.

 

Upper and lower Radiator hoses hot? Coolant fan may run continually? If so
you have a blockage in the cylinder head.

3.5L Engine: Drain coolant. Remove thermostat housing and thermostat located
on the lower left side of the block. It may be necessary to relocate the
accessories on that side to gain access. Remove the upper radiator hose from
the aluminum lower intake manifold water outlet (gooseneck) on the top side
of the engine. These engines use a different theory for regulating the
coolant into the engine as compared to a 2.0 or a 2.4. With the thermostat
removed (lower left of engine) you will notice a small drilled hole in the
upper part of the cavity about the diameter of a pencil. Use shop air and
blow air into this small hole, the air should exit at the top of the engine
on the left cylinder head out the lower intake water outlet (gooseneck). Use
shop rags to catch debris from re-entering the cooling system. Due to the
different design of the 3.5 versus the 2.7 it may be necessary to remove the
lower intake and possibly the left cylinder head to remove the debris. There
is a machined pocket in the cylinder head that can trap material easier than
on a 2.7 engine.

 

Thanks for the good advice. I'll do the combustion gas test first.
Hopefully it is negative and blowing out the tstat hole will produce
something, or at least I'll be able to hear something rattling around
in there.

 

Sounds like its got a trapped air pocket. Did you carefully bleed ALL
the air out of the system when refilling it with coolant?

 

Oh yes. Bleeding was done over and over until I realized that was
definitley not the problem (I have successfully bled this and other
cars)

I read a very interesting post on combustion gas getting into coolant
and test kits for same at
http://www.troubleshooters.com/tlitthypothesis.htm
If anyone has any input on combustion gas test kits please chime in.

 

Here is a link to the combustion leak tester and a pretty good
description
http://www.arrowheadradiator.com/head_gasket_or_combustion_leak_test.htm