Strange Overheating Issue

[lci240sx]

I've done a search and have been unable to find information concerning my issue so hopefully someone out there has some insight on it!

I'm running a '93 240SX HB KA24DE with 5-spd manual and I am having serious overheating issues. I have tried all the normal stuff like putting in a new thermostat, drain and flush the coolant, tested the engine temp sensor, etc. The radiator is a brand new high-flow Koyo (and was installed before the issue came up anyway but I'm just helping eliminate pieces of the puzzle).

General Symtoms: When shifting between 2nd thru 4th, engine temperature climbs rapidly and then settles back out when up to interstate cruising speeds of 65-80 MPH. I am unsure if the vehicle speed sensor is totally functional to control the radiator fan properly, but the fan only runs when the AC is turned on (which indicates that something is wrong between the temp sensor and the fan itself, I am only bypassing certain relays and ECCS controls to run the fan at all by running the AC). Basically the troubleshooting tree points to ECU, Radiator Fan, Fan Relays 1-3, and/or headgasket in the process of failing.

The car also has a rough, semi-seeking idle when the AC is on and a stutter problem when given approx half throttle during acceleration. This also points somewhat at the ECU (which could be retarding or advancing timing causing engine overheating?).

Does anyone have any information that might help me figure out exactly what is wrong?

Thanks in advance.

edit: My appologies for missing the sticky and posting in the inproper forum sub-section, please move if necessary.

[e_c]

do you have the stock mechanincal fan still attached?if not, you should get one or install an electric fan, cause the a/c fan just isnt cutting it

[lci240sx]

The engine mounted mechanical fan is still attached and the clutch for it seems to be functional. I was speaking of the secondary electrical fan attached to the engine side of the radiator.

Thanks for the input!

[USDM240]

thats not a secondary electrical fan. that fan is specifically for the A/C condenser. it will not turn on EVER unless the A/C is turned on. however, you can wire it up to function as an electric fan and just remove the mechanical version.

as far as your problem goes, sounds like youve just got some air in the lines and they need to be bled.

[lci240sx]

thats not a secondary electrical fan. that fan is specifically for the A/C condenser. it will not turn on EVER unless the A/C is turned on. however, you can wire it up to function as an electric fan and just remove the mechanical version.

as far as your problem goes, sounds like youve just got some air in the lines and they need to be bled.

I find it rather odd that both the FSM and ALLDATADIY.com both directly link that fan to both the engine temperature sensor and the vehicle speed sensor through the ECU and that it comes on based on temperature whether the A/C is turned on or not. I'm not going to say you are wrong because I do not know much about this car, but I'm well trained in how to read a technical document. Reference the attached image which I pulled directly off of ALLDATADIY.com to see how I came to this conclusion.

As for the air trapped in the system, I cannot vouch that it is ALL gone but it should not have any sizable air bubbles in the system considering I haven't had to fill the overflow tank back up since the coolant drain and flush I mentioned earlier.

Thanks for the input!

[e_c]

did you bleed the coolant after the flush?if not, there is a screw near the front of the engine, on top next to the TB, but on the block, it has a "caution dont open when hot" or something sticker next to it, anyway, unscrew it part way, so most of the threads are out, then uncap radiator, coolant will spill out of this hole, when it does, screw back in and make sure your rad. is full.. done

[K-1]

ya, seriously, make sure you run the engine with the bleed valve open (on the intake mani), but have someone waiting to shut it off cause once the last of the air is out, it will squirt at you (so have a towel around the bleed hole)

I did some work on my system, pump/thermostat, raplced all the fluid, the thing was overheating, after bleeding the air (not much air) it works perfectly and never overheats.

I think the KA's have a section of cooling channels that will trap air in the engine... that's why you need to bleed it.

[lci240sx]

Thanks for the input guys... I'll give it a shot this afternoon and see what happens!