Guys,
All said below is correct. Unfortunately there maybe so many reasons for overheating it is difficult to diagnose. Also typically there is not a single reason for overheating but a combination of several reasons. Diagnosis requires a chain of systematic steps to be followed.
Unless you follow all steps as described below in a systematic manner you will never have any reasonable certainty of what were the actual causes of your overheating In general the system requires:
Because some of the steps require dis-assembly of some of the ancillaries I suggest the following sequence :
Potential problem : RADIATOR If normal (not demineralized) water was used in a radiator (or coolant was not changed for a long time) the radiators build a residue and become ineffective. The residue I have seen removed from these channels shocked me. I did not know so much dirt can be in the engine and the engine still runs.)
Remedy : drain the system and flush !!! Make sure the flush fluid you use is suitable for aluminum heads !!! NOTE: turn the heater on when draining, flushing and filling. Take the radiator off ; use water hose to flush it. Go to radiator shop that repair old style copper radiators. Have it checked - if required replace it with the same capacity radiator. Best solution: buy a new radiator from Yagmur and install it. Also check electric the fan switch located in the radiator. Make sure it is low temp rated : I use Wahler 77 /82
( see :
http://www.eeuroparts.com/Main/PartDetail.aspx?id=8547572%2f82)
Again test it before installing and never buy ?no-name? low cost switches ? they work inconsistently and 80 % of them fail in first few days ! While at it check all the hoses ? including those that go to the heater and with any indication of aging wear replace them !!!
Potential problem : WATER PUMP Water pump circulates coolant in the engine. Properly working water pump is essential. Though I have not encountered a working water pump not to pump sufficient water it is really worth inspecting. Typical damage ? leaking and worn bearings. Also note it requires proper tension of the water pump belt. (Proper size pulleys ratio) should not be of concern unless these are not original. This ratio assures the water pump speed is sufficient (not too high though because this will damage water pump bearing).
Remedy : inspect and replace if required
Potential problem : THERMOSTAT There are different temperature ratings of these thermostats. The higher the temperature you use your car in the lower the thermostat rating required.
Remedy : test and if required replace the thermostat. Note : there is plenty of cheap and low quality thermostats around. Before installing (or reinstalling) take it out and out it on a pot of water and heat it up until boiling. Use temperature gauge (high scale thermometer) to measure ?begin to open? -lower number of the temp rating- and ?fully open? temperature The higher number of the temp rating). Even if you get a new one get it from a reliable source and test it anyway.
Potential problem : COOLANTCoolant serves few purposes : it cools the engine but it also prevents boiling and internal damage (residue buildup) in the water channels. The system is pressurized to reduce the boiling point with the radiator cap serving as a safety valve. To serve these purposes the coolant should be of proper quality (I always use Fiat Paraflu) in proper concentration and always diluted with demineralized water only !
Remedy : once you have removed the radiator and the water pump you must have drained the system. Flushing it before removal the radiator and water pump allows you to just refill it coolant. Note : Use always quality coolant concentrate ( I recommend Fiat Paraflu). Use demineralized water only to dilute the concentrate following coolant manufacturer?s instructions. In addition check concentration of the coolant with a simple tester (readily available in auto stores)
Note filling the water system in Fiat DOHC engines is tricky:
never fill through the radiator top but always through the water pump intake (!!!!) between water pump and thermostat. (always drain and fill on a cold engine and with heater on !!!) After filling reconnect the hose from the thermostat housing to the thermostat outlet again and run the system without the radiator cap for a while ? note air bubbles coming out. Top the radiator to make sure it is filled to the neck. When the fluid starts expanding and starts overflowing put the radiator cap securely. ( Note: the long neck radiators require special - taller- caps.
Final test : run the engine , the temperature of the hoses , running temperature , any signs of excessive temperature.
If the problem persists the problem is in the engine and it is serious !!! Several possible causes (typically at the same time: high engine friction and residue not removed (removable) from water channels by flushing, probably residue buildup in oil channels. You need to rebuild the engine of a new engine.
If however the problem is solved to the point that engine does not overheat, just runs hot ( 100-110 deg. C) you have an option to :
- use oil with high temperature resistance ( i.e. Castrol Edge sport 20w-60; Motul LeMans 20w-60 or Selenia racing SAE 10W-60) ,
- use slightly higher concentration of coolant in the system,
- use a lower temperature thermostat
- use a lower temp thermo fan switch,
- install twin fans / or a modern fan with much greater airflow capacity
Note these are all measures do not address the real root of the problem, just its symptoms. If the engine is not too damaged it may work even for few seasons.
Overheating was never the problem I encountered on my engines but running hot was almost always the problem with all my DOHC engines (except the one build by Guy Croft . It runs tops 85 deg C.) The 124 spider (2.0 fuel injected) tends to run a bit hot (especially in high traffic during the summer). In all cars I have a manual fan switch and always watch coolant temp closely.
Hope the above diagnosis list and tips are helpful.
Miro
Author
