Radiator fan not turning on

[micbrody]

Car cooling was fine; but had trouble with hot starts because of bad TTS.
I drained entire coolant system at bottom of engine block.
Changed TTS switch (Crazy difficult)
Filled with coolant.
Engine started both hot and cold; and radiator fan went on.

I then removed some radiator fluid from top of radiator; added some Bar’s Head Gasket Fix . I had thought a year earlier I might have had a tiny head gasket issue; but turned out I didn’t - but still had stuff. So I added for “preventative” issues.
I then started car; fan didn’t turn on; and noticed reservoir was full??!!
I let it cool down; inspected radiator cap; it had no primary gasket left; I ordered and installed new cap.
Started car; car still “overheated” -no fan going on- but at least reservoir was normal.
I burped at least three times and topped off coolant- but still no luck with fan.
I purchased new radiator switch; shorted it and fan went on.
(I also tested old switch and that worked).
Installed new switch; but again fan never came on.
I used IR thermometer: it did show temps of 170-190 in lower radiator hose inlet; and 210 at top of radiator - BUT 160ish near bottom left of radiator where thermostat.

I theorized that I needed to flush radiator. I drained it from lower hose and thermostat; no obvious crud.
I then inserted garden hose and flushed via top, and two bottom holes. Water flowed fine ; but first part of flush was very foamy. (Does that happen when flushing with garden hose?). I continued to flush a few times from all holes. Reinstalled lower hose and thermostat. Added coolant and burped. Started again but still no fan going on ; and temperature still cool at thermostat part of radiator; but 210 at top of radiator ; and 190’s at radiator bottom in inlet.


So:
1) is water pump not working now? Did the Bars head gasket fix do something to the pump??? Do water pumps “partially” work causing difference in radiator Temperature locations because of low flow; or is pump not at all working and hot fluid rising to top of radiator from hot lower inlet?
2) how can I easily check water pump?
3) can radiator still be bad?? Clogged where thermostat is? Or still air bubbles?

I’m very temped to just get new radiator and water pump; but I like trying to figure out

[18Fiatsandcounting]

Since the cooling was working fine before you did the TTS fix, my guess is that you've got an air bubble. There are many posts on this forum about how the Fiat radiator is lower than the top of the engine (in terms of the cooling passages), and how filling the system by the radiator cap can still leave a lot of air space in the top of the engine.

There are many approaches to address this issue, but the easiest is to put one of those "cooling T connections" in the coolant hose that goes from the top rear of the engine (and then over the exhaust camshaft cover) to the input pipes for the heater. Once you've installed the "T connector", do the last topping off of the coolant through that fitting.

I'd start there, but I'm also not discounting radiator blockages or a worn water pump at this point.

-Bryan

[rridge]

A fill port is a handy thing to have on the heater hose coming off the back of the head. If it doesn't fix the problem, here's a simple diagnostic for the electrical side of the radiator fan. Fan wiring varies year to year. This is for an '81.

The power for the fan comes from fuse "L" one of the 16amp fuses on the left side of the fuse box. The same fuse powers the horn. Tap the horn button and confirm the circuit is working.

Working from easy to harder, check the ground next. Auto electrical problems are often ground related. The fan picks up its ground from the grounding pod behind the driver's headlight on the inner fender. Start at the radiator switch. Trace the two black wires from the switch. One goes to the fan motor. The other goes to G1, the grounding pod. Pull the connector off the pod, checking for a tight fit and lack of corrosion.

Then run the engine and let it warm up while keeping a hand on the upper radiator hose on the passenger side. When it because uncomfortable to touch check the temperature of the upper hose on the driver side. It will stay much cooler until the thermostat opens and then will quickly reach the same uncomfortable temp as the first hose. You can confirm coolant is flowing by lightly feeling the lower hose to confirm that it is warming once coolant is flowing. Keep fingers and test equipment clear of the alternator belt, the water pump pulley and fan itself at all times.

If coolant is flowing and the engine is warming properly and the fan still does not come on, its time to confirm that the fan itself works. Trace the fan motor harness back from the motor. There is a two prong connector in the immediate vicinity. One wire is light blue and is bringing the power to the fan. You've already traced this black wire to the radiator fan switch. It connects the motor with its ground when a certain temperature is reached at the bottom of the radiator. Check that power is reaching the light blue side of the connector with a meter or test light and that the connector itself is corrosion free. Power is alway hot in that circuit.

Test the motor by providing an alternative grounding path. Disconnect the black wire side of the fan harness and and push a bare wire end into the female socket on the motor side of the connector. The connector design allows you to keep the blue power side of this junction connected while you disconnect the ground. Clamp the other end of the test wire on a bare plated machine screw fastened to chassis sheet metal or use the grounding pod on the inner fender behind the driver's headlight.

If coolant is circulating, the bottom of the radiator is hot and the fan motor is working with an alternative ground it's time to think about replacing the switch itself. And yes, fan switches are sometimes bad right out of the box.

[RRoller123]

[RRoller123]

Yep, so that fan turns on by the switch just making a circuit to ground, the Lt Blue at the fan motor is always hot, even with the ignition off. Can take a jumper and take that Black from C5 directly to ground and the fan will/should turn on. That at least will tell you if the fan is working.

[micbrody]

I appreciate everyone’s input. I have done most everything suggested other than bench test the new thermostat. However: the old thermostat did bench test functional.
Also: when I jump the blue and black wire, fan goes on (and horn always working)
The question I’m trying to figure out is why temperature difference between bottom inlet (when flow thermostat opens at 190) while temperature at top new radiator cap is 210 - but temperature near radiator thermostat at 160.
My theories:
1) poor circulation to thermostat part of radiator because of air bubbles
2) poor circulation because water pump not working to forcefully push hot fluid into radiator causing more homogenous mixing
3) poor circulation because of some blockage (physical) preventing hot fluid to getting to thermostat side

[micbrody]

I will try to burp the fluid more.
I will also make sure connector is conducting to actual thermostat ;
But at some point, I’m tempted to just get new water pump and radiator. Radiator looks to be original; not sure about water pump

[18Fiatsandcounting]

The question I’m trying to figure out is why temperature difference between bottom inlet (when flow thermostat opens at 190) while temperature at top new radiator cap is 210 - but temperature near radiator thermostat at 160.

Here's how I would look at it, which might explain the temperature differential. Remember that the water pump pumps coolant INTO the engine, not OUT of the engine. The coolant than progresses around the block, up unto the cylinder head, and then out of the outlet at the front top of the head. At this point, the coolant is at its highest temperature. It then flows into the top of the radiator, which is why the top is very hot. The coolant flows down through the radiator, losing heat as it goes, and so by the time the coolant reaches the bottom radiator hose, it could be 30-50 degrees cooler than the top. That cooler coolant is then pumped from the lower radiator hose back into the block by the water pump, and the process starts over. There is a thermostat in this coolant flow path, and its function is to limit the flow rate until the engine comes up to temp, at which point it opens.

-Bryan

[rridge]

Tthe most common explanations for a thermostat that does not open on engine even though it tests o.k. is that there is an air bubble in the thermostat. The next most common explanation is that the thermostat is installed backwards. Easy to do and very common. This video will illustrate the correct orientation. https://www.youtube.com/watch?v=-BqyZ3_rWEQ

Ignore the video's description of the flow path in the coolant through the engine. This too is a common mistake. But they got the thermostat installed correctly. Bryan has the flow path right in his description above.

[micbrody]

I might be mixing up terms:
I believe the “thermostat” at water pump has been working fine. The lower hose connected to bottom of radiator gets hot at 190 deg (though I thought flow went from that thermostat to radiator).

The fan switch thermostat is the issue.
I have had this car since 2014, and have drain coolant completely once before; and I was able to refill and burp without much problem. I have had the “prestone tee” on heater hose entire time.

To recap: the reason I drained system was two fold: it was time to change fluids; and also to change Thermo timing switch. Everything worked great initially.

And then I decided to make things “better”. I added some Bars Head Gasket repair; which I had read could be reasonable to stop minor head gasket issues. I had purchased a year ago, but realized everything was fine. So I used to to head off any future problems.

But as they say: the enemy of good is better.

After adding, the. Fan switch never went on. I ordered new one and exchanged. Still no luck. I took old one and and it bench tested fine.
I have burped so much not only is my garage floor full of coolant spots, but my own throat hurts. Car continues to go over 190 without fan going on. I have watched antifreeze gurgle out of radiator with cap off at start- telling me pump is working.
I have measured temperatures at different parts of radiator, and always cool by thermostat. I flushed radiator all different ways.
I’m thinking there is some sort of partial obstruction in radiator by thermostat. It’s probably time just to replace it (original).

Curious what radiator actually looks like on inside? Could the Bars head gasket stuff somehow clogged up a portion ??

[18Fiatsandcounting]

Curious what radiator actually looks like on inside? Could the Bars head gasket stuff somehow clogged up a portion ??

Yes, the Bars head gasket stuff could well be the source of your problem. It's basically a "goo" that flows around, clogging small pores as it goes, and then solidifying. The problem is, the goo doesn't distinguish between a real leak that you would like plugged, or a narrow opening in a passageway of the radiator.

My guess is that the Bars plugged up the coolant passages near your fan switch sensor, and so it never senses the hot coolant. The solution is to take the radiator to a good shop to have it cleaned, and if they can't, time for a new radiator.

-Bryan

[micbrody]

Yep...... hence the enemy of good is better.

The radiator is , I believe , original. When I bought car off Craigslist in 2014, it had a tiny pinhole leak in radiator; I used a radiator leak product that worked great.

I think the timing is just too coincidental - it’s probably clogged. I’m just gonna get a new one.

I need some opinions: should I also change water pump??? Or again- is that another “enemy of good is better”? (I have done brakes, suspension, electrical including rebuilding and coating AFM; however: I have never changed a water pump . Is this difficult?

[18Fiatsandcounting]

I have never changed a water pump . Is this difficult?

It shouldn't be, but the issue is the bolts that Fiat used to secure the water pump to the block. Often these are corroded or otherwise weakened, and then you have to deal with bolts that have snapped off. My suggestion: Get the water pump totally clear of other obstructions, and very carefully remove the bolts that secure it to the block. Tighten just very gently, then tighten slightly again, then loosen very slightly, etc. Use the penetrating oil of your choice.

Once you get the old water pump removed, a cleaning of the mating surface on the block, and a new gasket, should do the trick. Of course, there is that issue of the water heater return pipe (under the exhaust manifold) that can often give grief. Again, go slowly, use the penetrating lubricant of your choice, and learn some Italian swear words.

-Bryan

[micbrody]

Update:

Installed new radiator; retested the fan switch - turns on at about 200 on the bench test; reinstalled. Filled; burped. Still no fan going on; let cool; reburped and topped off a little air space; still no fan.

After running around, engine is fine when car moving. But when stopped at my garage; and then engine revved , the temperate gauge clearing goes past “0” of the 190 deg - half way to red zone; I then shut car down
My infrared thermometer reads 210 near the top of radiator; 195-200 near bottom hose; 190-195 at fan switch.

So actually fan switch shouldn’t go on at that temperature - so it’s still a “flow” issue.

I will burp again; but now wondering if thermostat not “fully opening” (could the Bar’s head gasket repair gunk up movement); or the water pump not as efficient (again ???Bars head gasket repair?; or just still more air to burp.

Good news: I have two good radiators

[18Fiatsandcounting]

It still sounds like you might have air in the system, but I also wouldn't rule out the possibility that the Bar's stuff has gunked up the thermostat. But, since the car stays cool when driving, I'm inclined to think it's a burping issue.

Your fan switch sounds about right at 200 oF. Mine (original) is labeled 92C 87C which I interpret to mean it comes on at around 198 oF and turns off at around 189 oF.

You can purchase fan switches that come on at a lower temperature, so that's one route. After you've convinced yourself that it's not a burping or thermostat issue.

-Bryan