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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).

Reply to
mkfdar
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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.

maxpower wrote:

Reply to
mkfdar

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.
Reply to
maxpower

Reply to
mkfdar

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

Reply to
Steve

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

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anyone has any input on combustion gas test kits please chime in.

Reply to
mkfdar

Here is a link to the combustion leak tester and a pretty good description

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Reply to
mkfdar

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