Radiator fan not kicking in and overheating mk1

Bit stuck on few cooling issues :thinking:

have just refilled engine after rebuild, heater matrix only seems to be blowing luke warm air even though pipe in feels fairly hot (heaters on full both fan and heat). Cars jacked up to aid the pushing of any trapped air out. Anything i’m missing? Temp gauge is very quickly going to high too?

Final issue is cooling fan won’t kick in, now i know it works from connector to fan as tested it. Sensors brand new along with thermostat in housing these have all been checked and fan kicks in fine when AC on.

Check that you don’t have an airlock in the cooling system. I’ve done this before in other cars after changing coolant. I turned heater on full with engine running and opened the radiator cap slowly to help get rid of trapped air. I also used to squeeze the rad pipes with the cap off to help the water circulate properly. It always worked for me.

1 Like

How old is the car? Early 1.6 fan control is a simple thermo switch, later cars have a PCM controlled fan. Is there a fan switch on top of the thermostat housing?

It 89 so has the thermo switch on top of housing at front. Sensor is new.

And if you ground the wire to that thermo switch the fan runs?

Yep tried the paper clip method in connector and grounded to cam cover. worked straight away.

If you leave it idling with the heater fan off does the cooking fan cut in or does it over heat? As said, looking like an air lock.

Havent tried with blower turned off yet to see if fan kicks in. but gauge seems to go straight to hot to suggest over heating, this has been within 2/3mins, but back pipe into heater matrix was still cold still at this point.

Not sure if my temp gauge is miss reading as read a thread on here yesterday night from a while back, where someone had similar issue and was gauge miss read. I did change 8months ago.so maybe did position back on securely?

Just bit hesitant to adjust this if is correct as don’t want engine to cook!

Have you left it to idle from cold with the radiator cap off? Does it push water out?

Yep did it few times yesterday, no bubbles just steam coming out in the end! Evening when squeezed back and front hoses.
And at some points coolant would come out at rad top

Is the thermostat opening? ie, top hose starting clod then heating up rapidly and water flow seen across the radiator through the filler cap.

Yep thermostat opens after temps up, and top hose gets hot then. as best as i could see coolant is following through top of rad through filler cap.

From all that then, it’s not really giving over heating symptoms by the sounds of it. If the water coming past the thermostat is hot enough there is no reason the cooling fan isn’t coming on. Is it because you have the blower on full that the water is not actually heating up enough to trigger the cooling fan, ie the blower is taking the heat away quicker than the engine can put it in. I wonder if your gauge is telling porkie pies. Maybe it’s worth having a look at that next.

Yeah thats what i’m starting to wonder as no it not issue or fault with temp sensor at back of engine as this is new after engine rebuild. hows best to reset it, do i use the thermostat opening at the front as the point temp gauge should be positioned at 12o’clock?

I’ll see if I can find the correct settings for it…

Thanks, found one on rev limiter but just says position the gauge in the middle when the engine is warmed up! :man_shrugging:

The workshop manual is pretty vague, it only gives 2 values, 182 ohms and the gauge should show fully cold and 20 ohms and the gauge should show fully hot. So I suppose when the gauge sensor is reading 80 ohms the needle should be in the middle ish.


In the past when thermostats and sensors were much less reliable I used to hang them in a pot of water on the stove and slowly heat it up while monitoring them, and also the water temperature with a cooking thermometer. (Both are hanging high in the water and NOT resting on the bottom of the pot.)
I still do this, but recently they have all been spot on, and it is only force of habit, and the worry about fake parts, making me still do it.

In the 1960s, 70s and 80s we used to find about one in three of the waxstat types was off temp and about one in ten never worked at all, this for Jag, Ford, BL, and Vauxhall. Some stats had a tickler to let past air and a tiny flow of water and this had to be at the top when installed as a guarantee the bulb was always in the water.

Sensors were usually much more reliable. The gauge ones either worked or were open circuit. But the switch type as used on the Kenlowe electric fans we all added tended to be less reliable, and a standard mod was to use instead a linear sensor and potentiometer and a couple of transistors to drive a relay.

1 Like

Thanks will give that a try then.

I got round to hooking my multimeter up to the temp sensor today, some reason the ohms mine gave out were different :thinking: seemed to work though, start off at 700 and when got 250ish i switched back to temp gauge connection and set temp at 12 o’clock, ran for 20mins more, needle virtually didnt move and if so was only slightly to the right. hope that will mean more of a true temp read?