overheating problem why???

[280zgod]

ok the other day my 75 280z with efi started overheating. it has a bigger radiator, oil cooler, and electric fans and normally runs well below or at the bottom of the4 temp guage even at full throttle. I have replaced the radiator cap, water pump, thermometer, and flushed and refilled the cooling system. there are no leaks from the coolant system that i can see. also my car normally runs extremely rich (dunno why) but anyway i checked the spark plugs today and they were blistered white. Anyone have a guess as to the problems? any suggestions would be nice.

[Bambikiller240]

Are you *sure* the elect. fans are coming on when needed? Could be a wiring issue, or the temp sensor that activates the fans.

[JLPurcell]

You might want to check a couple of things: A pressure test on your cooling system. A head gasket leak will cause your plugs to look white and clean but it is unlikely that all the plugs would look that way. It could be a fueling problem a lean charge will make the plugs white and the engine run hot. If the intake manifold is leaking unmetered intake air you can also get a lean hot situation. :nervous: I take it you have checked the basic set up on the ignition etc. JLP

[280zgod]

yeah i was thinking that the lean issue might be the problem i just dont know why its running lean. i dont think there are anymor leaks into the manifold since the idle is stable at 700rpm and normally when there is any leak at all from the manifold the idle jumps to 2k or more. as for the head gasket i replaced that about 2k miles ago when i had the head rebuilt adn all the timing parts and gaskets replaced and its worked fine up until two days ago. i drove it fine all morning then later that night i start it up and it overheats im thinking its something wrong with the efi system since it always is a problem with that thing. but ill see what i can do ill play with my unadultered AFM and see if that can correct the leanness and if that doesnt help i dunno what to do. thanks for the input guys.

[280zgod]

well i tried messing with the AFM and it didnt help car still overheating and now a new mystery warm water makes into the heater hoses but not into the lower radiator hose so im thinking maybe a clogged passage from the water pump somewhere??? i dunno has anyone ever had clogged coolant passages on their z?

[Bambikiller240]

Is the water at the top of the radiator hot? (Upper Radiator Hose) And is it cold at the bottom of the radiator? (Lower Radiator Hose)

If so, it is most likely that the radiator itself is plugged. This is FAR more common than "a clogged passage from the water pump somewhere". The passages in the radiator are much smaller that either the inlet or outlet of the water pump.

Water flows from the front of the cylinder head into the top of the radiator, through the radiator and out the lower radiator hose. From there it goes into the water pump which forces the water into the engine block and up to the cylinder head again.

Hot water from the fitting at the rear of the cylinder head (passenger side) can reach the heater hoses even if the radiator is plugged up.

You might want to have the radiator checked for proper water flow by a competant radiator repairman.

[beandip]

I know this is along a different ave , but after you pressure test the systime , check the timing. If retarded it can cause over heating . Another thing did you retork the head bolts since the installation ? You might check and redo them even if the pressure test shows it is ok. I dident and was told to after my Maxama reached a certain milage , cant remember now what it was , I think 5000 miles maby less . anyway I blew a head gasket . After that was repaired I retorked the head at 500 miles and never had a problem. Gary

[280zgod]

i havent checked the timing yet since id been checking it every week to make sure it wasnt off cuz the car does this weird thing but anyway. the water in the top of the radiator is ice cold and the water at the bottom hose is boiling hot. no water ever makes it to the top hose as far as i can tell but since i did get a new thermostat maybe thats the problem. my car normally runs so dead cold that maybe with the new thermostat its heating up to be able to open the thermostat to let water out i dunno im rambling. anyway yeah im totally lost but ill retorque the head down cuz i havent since the head was torqued down when i redid it. see if that helps.

[Bambikiller240]

From your latest description, it sounds like possibly a bad Thermostat was installed. You did install it in the correct orientation, right? (with the mechanism down) In any event it seems that it's not opening.

[280zgod]

but the problem was occuring before i changed it out and then again i guess it couldve been the old type where if the car overheated the thermostat would lockdown and force an overheat hmmm. is there any problem with just removing the thermostat all together?

[280zgod]

when i redid the head i got a new radiator one of those bigger ones from msa since my old one had a hole its only been in for about a month month and a half.

[Bambikiller240]

The car is meant to have a thermostat in it to regulate the engine temperature, if you remove it, the temperature will not be regulated.

If the water in the top of the radiator isn't getting hot, "something" is wrong. I'm still thinking it's a defective thermostat not opening or it is installed backwards..

Have you replaced the water pump?