Hi,
New to the forum and Volvo . Just bought a 1992 740 non turbo a couple of weeks ago . Love the car . It needed a header intake valve replaced to pass inspection. I replaced it and brought it for inspection . As the gentleman was about to put the sticker on the windshield the car overheated. I told him there was no turning back now and to put that dang sticker on the windshield. He did.
Anyway, does anyone have a guess as to why the car is overheating while parked ?

The fan works when either the a/c is on or the defrost . Otherewise it will not kick on . I replaced the thermostat and the coolant temp sensor for the computer. Still can't get the fan to kick on . I haven't replaced the coolant temp gauge sensor yet . It seems to be working normal . Now I'm wondering if it could be the wiring or something else .
Any ideas and / or suggestions would be greatly appreciated .

Thanks

 

What's a "header intake valve"?
Did you replace the switch on the radiator, two wires, upper passenger side? It's the one that controls the fan...

 

Sorry I was thinking of too many different parts at once. I replaced the front exhaust pipe (duh) . I will give the switch on the radiator a shot.
Thanks for the reply

 

the engine coolant temp sensor is used purely by the fuel injection and ignition computers to know how much gas and what timing to use (retard when cold, etc). the temperature gauge sensor is used soley for the dashboard gauge. as lev says, the switch on the radiator is what controls the fan.

 

Thanks . Where exactly is the switch? Are we talking about the cooling fan relay that's located between the radiator and the right headlight ? Closer to the headlight ?

Thanks

 

I cannot find a cooling fan switch on the radiator like I see on some of the older models . There isn't one on this radiator . The only thing that I can find is the cooling fan relay. Thanks

 

lemee see. got the 1992 740/940 Greenbook Wiring Diagrams here, (I have a 92 745T)

ok, this shows it as a 2-speed fan, the green wire to the fan is low speed, the red wire is high speed (and ground is black)

at the relay, 1C is the low speed output to the fan, 2C is the high speed output to the fan, 1A is the power input to the battery (red wire)

1B comes from the low speed pressure sensor, and the ECU, and if either of those grounds that pin, the low speed relay switches on.

2B comes from the ECU, the thermostat switch, and the high speed pressure sensor, and if any of THOSE grounds that pin, the high speed relay switches on.

the low speed and high speed pressure sensors are both on the AC condensor manifold. the termostat switch should be on the upper right side of the radiator.

 

Thanks pierce . There is no thermo switch on this radiator. Only the wires from the fan motor to the relay . Not sure what this could be. My only guess at this point is to replace the relay

Thanks

 

let me look at my 92 turbo 745 to verify if that switch is used. sometimes the schematics show optional things, like maybe the switch is only used with Regina, and LH does it via the ECU (ECU reads engine coolant temp and tells fan to run high or low as appropriate).

as a test of the relay, if you ground pins 1B, you should get a high speed fan, and 2B should get you a low speed fan. if those both work, then your problem is NOT the relay.

also, with an LH 2.4 car, DTM # 3 in jumper position 2 on the OBD box will do a fan test at both speeds controlled solely by the ECU, along with a bunch of other tests (idle air control, injectors, etc). See the DTM3 procedure here, Engine and OBD Diagnostic Codes (no tools are required)

 

A '92 745 NA should have that switch in the radiator... Pretty much all years NA's have it there: two pronged blade type thermo switch, a BLK and a BLK/WHT wires go to it.

Since you just bought the car, I bet the PO put another radiator without the switch hole... Look for the wiring, it should be tucked there somewhere...

 

Lev, that was my thought too . I looked for the wiring and didn't see any . Is it possible that the car could be a late '92 year build where Volvo used a different radiator or do all of the '92 740's have that switch . This kinda stinks if I have the wrong aftermarket radiator installed in the car . Does that mean the only option is to install the correct radiator and install / wire that switch along with it ? Oh boy !

 

I have a folder with the work that was done on this car . I just found a receipt dated 8-9-00 . Replace cooling fan thermo switch . I can not find a receipt for a new radiator but I bet one was installed(the wrong one) sometime after this date .

 

ok, I just checked, my 1992 turbo does NOT have the switch, nor is there any wire for it. it relies on the ECU to control the fan (overridden by the AC pressure switches).

 

On the top right side of the radiator there is a black plastic plug . Could the thermo switch have gone in there or if need be can a new one go in there ?

Thanks

 

Oh Thanks Pierce . So it is possible that my 92 non turbo may not have that thermo switch ? If that is the case what to do to try and fix this from overheating . Could it be the cooling fan relay ?

 

run DTM #3 in the diagnostic port #2 per that URL I gave above. your fan should cycle low/high/low/high during the fan part of the test. if this works, then your fan and its relay is fine.

 

Pierce , I ran the test . I should forewarn you that it was my first time running that test ever. The fan didn't actually come on but you could hear the click / signal being sent . It was low/high/low/high/low/high/low . The red light flashed ins sequence with the clicks . So now what ?

 

Oh and thanks for all the help Pierce and Lev . I really appreciate it.

 

The Turbos don't have the switch, the NAs do. This applies to the '90's cars... The switch is the "push in" type, plugs in a rubber plug that sometimes pops out. I am sure your '92 had it at one point...

 

So somewhere along the way a radiator for a turbo got put in this car I'm guessing . Any suggestions on what to do ?

Thanks again