Engine seems to overheat if aircon isn't on all the time

[shadetreemechanic]

Gday,

So I've spent a bit of time searching the forum and a few ppl have the same issue as me but no real clear answers so far. Here's the situation that's been bugging me:

When stopped at the lights, I need to have my aircon on to keep the thermo fan running to keep the engine cool. The fan naturally kicks in at half on the gauge (no aircon) but by that time I can feel the engine is way too hot. Its radiating heat if I stick my arm out the window and runs and sounds like a pig. If I switch the aircon/thermo fan on, temp sits on 1/4 (or just 2 bars from Cold) and all is well.

I've replaced the radiator, water pump, thermostat, coolant 50/50 spec. Also bear in mind this is a VR with only 1 speed thermo fan. So I think the relay is fine since the fan will work at 1/2. Do you think it's the coolant temp sensor that's faulty?

Cheers

[calais_cruzin]

Temp sensor is cheap, so id just grab one. Atleast u will know that it will be reading the right temp.
It could be the fault, not knowing the temp to turn the fan on and the air con is the only thing keeping it cool while ur stopped.

[wortus]

I think you can run a test by disconnecting the temp sensor for the ECU and start the engine with the aircon off and this will make the fan run if the circuit is working? I may be wrong but I recall someone mentioning that on this forum?
The temp sensors for the ECU and gauge should be within a certain resistance range, you can check this with a multimeter and you should be able to check the gauge by substituting known resistor values for full, half deflection etc? You just need to find out what these resistances are and an auto elec or an instrument repairer should know.

[shadetreemechanic]

Yeah I may as well do it, it's the last thing I can think of and can't hurt. So I should grab one from Holden? Repco ones no good?

[Michelson4301]

Nothing wrong with your cooling system by the sounds of things. Don't want the fan working all the time, only when it needs too like in traffic. On the highway i bet it the gauge drops within 5mins without AC running. Engine will get hot to touch, fan comes on about 98degC. If you think there is a problem get your mums thermometer and put it in the radiator filler or use a raytek.

[shadetreemechanic]

Yeah Michelson on the highway its fine since there's heaps of airflow. I don't want the fan on all the time but I'm pretty sure its getting too hot at the lights. Taking off she rattles and pings heaps definitely not normal I reckon

[shadetreemechanic]

Just an update to say I only replaced my radiator cap and so far it seems to be holding temp better...

[Brett_jjj]

The thermo fans are meant to kick in at around the half way mark on the temp gauge.A few people on here have said that theirs doesnt even come on at 3/4 or higher on the temp gauge,and that this is normal.My VSV6 fan kicks in at the half way mark on the gauge.Ive found that most of them kick in at around the half way mark..