Overheat in Traffic but Fan Working

[moss1972]

Hi folks,

I purchased a new aluminum radiator and 14" fan assembly from Auto Ricambi. Part SKU: CO2-418. I installed these along with a new water pump. I also have a new 170 thermostat. Everything works flawlessly except for in one situation.

If I'm driving on a hot (high 80s and hotter) day at highway speeds, then get stuck in traffic for more than 5 minutes or so the temp starts creeping. She will stay shy of the red warning area but definitely is over 200. Last night I almost pulled off the road, but traffic picked up to 15mph and she started coming back to 200 then normal levels after that.

When I got home and parked it she was at 190. I got out and of course the heat buildup caused the fan to come on and it ran about 45 seconds before shutting off. So, the fan is working.

If the fan (stock switch) is working...and this is a new radiator with a supposedly higher airflow fan...what could be the bug in the system causing this near overheat in these conditions?

Thanks!

[seabeelt]

If there is any air in the system the car will run hot/overheat when air flow is minimal

[moss1972]

Funny you mention that. I went outside today and the top line to the radiator seemed to be half full by feel. Gonna see what needs bleeding. Thank you!

[aj81spider]

Not that I know anyone who's done this - but make sure the fan is running in the right direction. If you get the wires backward it will run in reverse - and not be very effective.

[manoa matt]

The fan switches come in a range of temperature cut in and cut out temps. Verify which one you have. They make ones that turn the fan on at a lower temp, IIRC the stock switch is set to come on and modulate the temp around 190-200 deg. F

[moss1972]

Verified fan is blowing in correct direction, polarity is correct. Also turns on at desired temp.

So I did find air in the top hose that connect to the radiator. Bled it and filled it. Then drove it. Was better but still the fan did not cool enough to shut off.

Found more air. Bled again. Drove it, put front tires on ramps. Bled more air out of T. Filled it. Ran it and the fan cycled!!!!

Took it off ramps and would not cycle.

Drove it, ramped it and bled it again. Drove off ramp and it ALMOST cycled. Drove it, ramped it and let it cool a bit. Bled again, ran cycled. Took off ramps, fan cycled!

I think there’s still a bit more in the system but I left it on ramps for the weekend and will bleed again to tonight.

Just wanted to post up the saga in case anyone else deals with this. Told my buddy and he says “I hope you don’t have gasket blow by”. I was like, “thanks! Something else to fret about.” LOL

[aj81spider]

A common and very helpful modification is to put a coolant flush T in the hose going from the top of the engine to the heater, through the fire wall. This is the highest point in the engine. After you fill it as far as you can through the radiator you put the radiator cap back on and open the flush T and then fill from there. Because it's the highest part of the engine it lets the air escape. I've done this on my car and have had no issues filling the coolant since then.

Something like this:

https://www.amazon.com/Dorman-Help-4715 ... 903&sr=8-3

[moss1972]

A common and very helpful modification is to put a coolant flush T in the hose going from the top of the engine to the heater, through the fire wall. This is the highest point in the engine. After you fill it as far as you can through the radiator you put the radiator cap back on and open the flush T and then fill from there. Because it's the highest part of the engine it lets the air escape. I've done this on my car and have had no issues filling the coolant since then.

Something like this:

https://www.amazon.com/Dorman-Help-4715 ... 903&sr=8-3

I do have one and was filling there too. Problem is air got trapped in the top 1/3 of the hose from the T to the radiator. So coolant would come out the T or radiator. The air wasn’t being displaced.

I had to put a small funnel in the T hole to raise the elevation higher than the hose then pull the hose going to the top of the radiator down while squeezing to get air up and out the T into the funnel where it could suck in coolant to displace the air. Then quickly replace the funnel with the T cap so air would not be let back in.

[18Fiatsandcounting]

You don't want a large air bubble in the cooling system, but you don't want zero air in the system either. The reason is, when the engine heats up and the coolant expands, if there is no air pocket at all, the expanding coolant will immediately be forced out through the radiator cap into the overflow tank. You want the engine to pressurize to "around" 5 psi when warm, and so you want a small air pocket so the system isn't constantly moving coolant in and out through the radiator cap.

A total guess on my part, but an air pocket of a cup or two in volume should be fine. The system holds roughly two gallons total, so two cups would be around 6% of the total volume. If the engine overheats when missing 6% of the coolant, something else is wrong.

-Bryan

[Nut124]

Since your thermostat is lower temp than factory, you will need a lower temp fan switch as well to prevent the high temps when not moving.

[moss1972]

If I had to guess…I probably added 32oz of fluid. An easy quart. So yeah… given the fact that I was able to get the fan to work properly my guess is it was the air pocket. Now, if air keeps appearing in the system in the problem repeat itself there could be blow through but I’m calling shenanigans on that one because if the problem were that big I think I would see it in other areas. Like, potential back bleed into the block when the system is pressured and the engine is off such that it could potentially get down through the seals and show up in the oil. Or some sort of problems starting which there is none.

I’m not ruling it out I’m just calling it unlikely. Also a good point on the switch temperature as well

[18Fiatsandcounting]

Another source of increasing amounts of air in the cooling system is when the coolant level is too low in the overflow tank. The engine heats up, the radiator cap opens to relieve the pressure, but when the engine cools back down, only air is drawn back into the radiator if the overflow level is too low. After several cycles, you can end up with too much air in the radiator/engine.

The overflow tank level should be at least at the minimum mark, and I usually aim for the tank to be about 2/3 full.

-Bryan

[moss1972]

Another source of increasing amounts of air in the cooling system is when the coolant level is too low in the overflow tank. The engine heats up, the radiator cap opens to relieve the pressure, but when the engine cools back down, only air is drawn back into the radiator if the overflow level is too low. After several cycles, you can end up with too much air in the radiator/engine.

The overflow tank level should be at least at the minimum mark, and I usually aim for the tank to be about 2/3 full.

-Bryan

The tank was a little low which, as summer kicked into gear, may have exacerbated the problem. Now I’ve got a good handle on it I know how to address. 100% of the cooling system is brand new. LOL

[Leonard124]

I don't know if this would help...but I always bleed the system with the front end of the car jacked up a bit.

Also bleed with the heater valve open.

[moss1972]

So I’ve done all the things. I found a leak in a hose. Replaced. Bled it such that today there was no air up at the T with the car on ramps. Mind you I drove it 12 miles and also Opened the heater core.

I checked voltage at fan 14v with engine running. I cleaned every fan connector and tab with sandpaper. Replaced switch lead wire clips and used dielectric grease.

Fan will hold temp at 200. Does not come down to 190. It was super humid and 85 today. Good for a test. She did good in traffic but sitting the fan won’t cool enough to cycle off.

This is an upgraded 14” fan too from Ricambi.

I’m beginning to wonder If the stock fan was more powerful.

I’m at a loss. Should the fam be holding temp or cycling off? I feel like it always cycled off before I replaced the water pump and radiator.