Ok, I have searched this topic and all I can find is "remove thermostat"

I have a 1994 240sx STOCK EVERYTHING....When I bought the car it ran very hot, So I started from the what I noticed was bad, Fan shroud was messed up, REPLACED...
Still ran hot, Then I just said the hell with it and replaced the radiator and cap with a known good unit, Still ran hot....
Looked up on TR and it said that KA's thermostats suck and to just take it out...When I dug in there to get it I Replaced the cracked Clutch fan and Noticed there was NO thermostat already....so I added one...and now it overheats so damn fast its not even funny....like it gets mid way on the heat index sits there for a minute and you look away and look back and its at the "H".... Now The last thing I can think of is water pump...MAYBE theres something on the KA motors that gets stock or plugged up before I tear out a possible good water pump...Just asking advice.
Jeff --- Dave any thoughts....

 

You might be able to check the water pump. Fill the radiator to the top then start the car. If the water pump is bad the water will not move. If the water level goes down then the water pump is working. I'm not sure if this will work on a 240 but it worked on my camaro, and my wifes millenia.

 

are there signs of leakage? a sure sign of a water pump going bad is to check the 'weep hole' located on the underside of the water pump...kinda hard to see and get to with the stock fans on and such. it wont always leak enough to tell either, but if you notice any coolant on your crank pulley or belts after turning the car off (wait a few min) that's probably the case.

the other thing is to make sure your fans are actually working. the clutch fan mechanism can go out but its more likely the secondary fan used for a/c and when the temp gets over a certain point, isnt working. you can tell if part of it is working if you turn the a/c on and hear it click on and you can see it if u put your head over the engine and look forward into the shroud.

or you might have air in the system. turn the hvac controls over to the heater hot side in the car and then run the car and top it off, you might have to let the car cool, open the bleeder valve and do it per FSM specs, which sucks.

 

Damn Dan.. right on it. The water pump is a $35 item and takes 20 minutes to replace. The fan has a clutch on it, which itself is replaceable, and is usually a culprit of overheating. The odds of the 2ndary fan causing this is pretty low. Bleed off the system as stated.
Next, is it really overheating, or could the temp sensor (one of the two on the intake manifold. the one with 2 leads going to it) be going bad and throwing the gauge off?
-Jeff

 

my gauge is being tricky lately too. it takes longer for the needle to rise, and when i get into boost it dips cooler by a tad bit....i know my turbo system isnt that efficient. i checked it today and wiggled the shitty one pin sensor on the upper coolant neck by the head...i think its on the fritz. car runs fine however.

funny thing is, i replaced my 'weeping' water pump about a year ago with the one off my spare motor in my garage, and to this day, i can't tell if maybe the RTV messed up or it's trying to 'weep' a little too...either way i have the slowest coolant leak in the history of man..not even enough to make leak spots on the ground...there is slight coolant on the crank pulley and lower belts after i shut the car down, but its so hot it evaporates before enough of it can start dripping. i top her off about once a month or so, just too lazy to get a new one and change it out...


btw where the hell do you get $35 KA water pumps? courtesy is like $70, local dealers are even more, and discount auto ones have been known to have shitty impeller blades (smaller).

 

Discount blades look exactly like stock, from what I remember. Autozone blades (which I have, unfortuneately) aren't dramatically angled like stock/discount. They're.. wedges. Autozone = no. Discount = Yes. However, my autozone special hasn't let me overheat once.
-Jeff

 

Also when its overheating, make sure both hoses are warm...if the top hose is cold, and there's no thermostat in, then you have a blockage in the system...usually in the heater core...you can try bypassing the heater core...connect the heater hoses to each port on the back. then if it runs at normal operating temp...you know where the blockage is. Lately the clutch mechanism has been going out on 240's...heard about a lot of them. waterpump could be the culprit...but also feel different areas of the radiator...i got a brand new radiator, and there was a blockage in it, which had me stumped for a month or so.

 

Ok, I replaced both sensors....water pump, and the clutch fan came off a running driving S14 car that never overheated....
I have also since removed the thermostat based on S86D ( dave ) recommendation...
The car takes alot longer to get hot now but it still does....
I have bleed the system out took some time for the bubbles to go down but they eventually did. Although I still see a bubble every few minutes....
But heres the thing.....
I can let this car run for 5 seconds after its been sitting for HOURS..and the radiator is fully pressurized and when I pull the radiator cap it wants to explode but the car is not even hot yet and hasnt been running long enough to be fully pressurized.
My conclusion, Along with a friend of mine, we are thinking that there may be a headgasket problem...compresion leaking from head into the water way..causing the overheating, excesive bubbles and pressure problem...If this sounds right let me know and how hard is a headgasket on a KA...( never done one before)

 

head gasket on a KA isn't fun...takes about 4 hours for me...probably 2x that if its your first time. There is a tool you can buy to check for hydrocarbons in the coolant that will tell you if there's a headgasket out. otherwise check the usual signs...oil in coolant, or coolant in oil. oil will look milky and lighter than normal. check those signs i mentioned above, before you try a headgasket.

 

I have already looked for those signs, thats why I ruled it out before...I have

Clean Oil
No Smoking exhuast
Clean Coolant

Im not wanting to do a KA headgasket..lol, I have done many headgaskets in my time as a mechanic I just dont do a ton of KA stuff. Im going to go check the heater core hose Idea now..I also sprayed a hose in the thermostat hole while I had the pump and thermostat out and the water moved pretty freely to the waterpump side.
My friend works at BMW and he has that tool and its stuck at is shop in sarasota, my luck.lol