aengine overheats at higher speeds only

[MCCIRE]

I searched for this already. I have a 90 240sx KA24e all stock 5spd m/t. I get on the interstate, it overheats. Drive around town no faster than say 55mph and she's fine. I just went through and changed the waterpump, fan clutch,rad hoses upper&lower, upper temp gauge sensor(next to bleeder), rad cap, all 3 belts, and flushed/bled the system CORRECTLY. There is NO thermostat in it. I just tossed it out. Hey, I live in f**king FL. Now, is my radiator bad (its the oe) or what? I also want to know what the hell a (2nd?) temp sensor is doing in the lower rad hose. What does that control? Wouldn't it trigger an electric fan on most cars?

[ShaunakaRichard]

Ya your thermostat is really important. Your going to overheat without it.

[MCCIRE]

Now why would it overheat without the thermo? If it opens when hot? Doesn't make sense.

[ShaunakaRichard]

Doesn't give the coolant leaving the block time to cool down, just keeps recirculating non stop. Going faster and a higher RPM would mean the water pump is pushing water through even faster and its constantly getting back into the block. Theres no cool water in the system that way. I know from personal experience not having the thermostat in will lead to over heating.
Modified by ShaunakaRichard at 12:26 PM 4/20/2009

[Steady_One_S13]

^ I agree.Get yourself a Nismo thermo......install it and call it a day. You'll be happy with it.

[MCCIRE]

Hey Thanks. Gonna try it and repost.

[youngun21a]

I had the thermostat off since my rebuild..and had no overheating proablems and have 10k or more on the engine..

[MCCIRE]

OK. So, I hesitated pulling the thing apart and putting the thermo back in (had to order it anyway) and tried a few things. While the engine was idling at Reg temp with no thermo i hit the gas from the engine and saw the upper hose just collapse for a sec. This occured several times only at higher rpm. I also took several short trips at night and day, the same distances etc and it did/didn't overheat for each variable. So I now know that it can either run hot or normal without changing a thing. I have a straight factory rad coming in from Jersey to FL so we'll see if that helps.

AND! WHAT THE HELL IS THE SENSOR IN THE LOWER RAD HOSE FOR? THATS THE ELECTRIC FAN SWITCH/RELAY RIGHT? THESE THINGS HAVE DUAL COOLING FANS? ONE CRANK DRIVEN ONE ELECTRIC RIGHT? JESUS I MUST BE AN IDIOT....LORD HELP ME

[greencar]

Have you checked the Radiator cap, check it with a new one or known good one, and try it again. overflow tank clogged?-Dan

[driftiteasy0113]

i believe its probably the thermoor check your block...see if freeze plugs are leaking?

[SullivanRacing06]

itll over heat without the tstat because the tstat slows the coolant down when passing thru the rad so it has a longer time to spend in the rad

[MCCIRE]

No leaks or anything. Rad cap is good and new. But I'm still waiting on the new rad before I go tearing things apart.........another day or two....will update.

Still, does anyone know what the deal is with the stock electric fan? Is it a/c or what? What does it cool?

[lukbot]

electric fan is for the ac condenser. it comes on with ac request depending on engine coolant temperature, ac pressure and ambient air temp. at least i think the 3rd condition is ambient air temp. may be vehicle speed, will have to check the fsm.

[lukbot]

sorry for the double post. 1 temp sensor is for the ecu signal 1 is for the temp gauge in the dash.

[AZhitman]

Dumb response, possibly but...

I've seen this when the fan is reversed.

Make sure it's PULLING when the car is sitting still (should suck a piece of notebook paper right against the radiator at idle).

Now, I've only seen this happen on cars with e-fans, but who knows.