B4 12V coolant temp behaviour

[cgharibo]

I have three 12Vs. '96 Cabrio and '95 90q run quite cool. The temp dances around the thick line regardless of circumstances.

My other '95 90 goes way past the thick line before fans kick in. I've jumped the 3 wire temperature switch at the radiator and the low and high speed fans come on fine. I've tried a lower temperature switch but the temperature still goes way past the thick line and just before the thin line before the fans kick in.

What do I check/replace next? I have a case of my fans kicking in late but the wiring checks out.

I was considering replacing the thermostat next. Thoughts on that?

Thanks!

[John.]

12V ??......you mean V6 yes?!

[cgharibo]

Yes, V6 12V. Thank you.

[K Simmonds]

I would replace the fan switches on the bottom of the radiators with good quaility ones then wire them properly, if the bottom hose is getting hot in good time then it's not the thermostat. I had problems with my C4 2.8 AAH engine with the fan kicking in at random times and normally too early and replaing the switch cured that problem.

Also as your in the states I expect at least one of the cars has air-con, in which case the fan will come on whenever the sytem is activated and this totally normal, but having the correct, working fan switch is essencial for this system to function correctly.

You could also clean the contact's to any coolant temp sensors you can get at and make sure the boots aren't filled with water, though I think this problem may only be an issue on the five pot engines.

Changing the theromstat on a V6 isn't much fun so it's not a job I'd do just for basic maintainance if it's workng correctly and opening at at around 87/88C. Thermostats tend to either work correctly or not at all, either staying closed or jamming open, both of which are easy to diagnose by feeling when the bottom hose gets hot.

Fan switches however are simple to change and not highly expensive, though either get a Behr or a genuine one.

How many pins do your fan switchs have? I only ask as I've only ever dealt with V6 car without air-con aside from my 30V and can't recall the pin out on the switch.

[cgharibo]

The contacts are clean. The AC button doesn’t turn the fan on but it may be too cold for that.

I will check the bottom hose to evaluate thermostat function.

Thank you for the great advice.

[K Simmonds]

No problem, hope you get to bottom of the problem soon, the first two cars you mention sound like they're behaving correctly if they hover around the center of the coolant gauge.

As it happens I really like the 2.8 12 motor, they go pretty well if everyting is working correctly, even in my heavy old C4 Avant quatrro. I had a 30V C4 Saloon for a short while before smashed iit into Landrover which didn't end well at all. That was a bit faster my 12V 2.8 but not as torquey feeling, though I expect that's illusion due to the 30V having a bit more top end.

If the bottom hose get's hot instatntly or very quickly depending on how cold it is, the thermostat is stuck open and must be replaced. The hoset should start to get warm just before the needle on the coolant gauge reachs the middle assuming that gauge is reading correctly. Then the fan should kick in just after the needle passes the center of the gauge assuming the AC is of. If the AC is on the fan can kick in at pretty much any tempreture unless it's very cold.

Just a thought, what is the ambeint day time tempreture where you are in the USA? I know it can vary wildly from southern Georgia to somewhere like Northan Idaho which is basically Canada.

Anymore question fire away. I'm sat at home with Covid so am at my keyboard, I'm too old to be posting using a smart phone unless I have to.

[cgharibo]

Our daytime temps range from 25-45 degrees. I’ve replaced the temp switch at bottom of radiator several times with different specs and it makes no difference in high/low fan behaviour.

I will check the bottom hose behaviour and report back. I suspect my thermostat is closed.

Thank you.

[K Simmonds]

That's pretty much same temp range as here, about -4C to +8C, if the bottom hose is getting hot very soon after starting the the engine then the thermostat is stuck open as you say.

Best reffer to '12V.Org' from a how to on that job. For some reason my computers anti virus doen't like the site but there's nothing worong with it as far as I can tell, it works on my phone fine.