Lower Radiator Hose / Flushing Cooling System

[moss1972]

Hi All,

So I have read all the first-page google search returns related to flushing the Fiat Spider 2000 cooling system. Replacing the coolant. When it comes to burping the system it's starting to sound like a religious experience. Some claim it's very simple, other's seem to veer off into the nether lands of electrical problems and fixing things that weren't broke when they started.

It appears to me that the only kink in the system is where the lower radiator hose rises up the thermostat. Yet...nowhere have I even seen someone suggest to REMOVE THE LOWER RADIATOR HOSE from the TSTAT and start filling the radiator from there...then re-attach it and continue to fill the radiator / system / flush T or whatever your method.

How silly do I sound in my logic?

Steve

[joelittel]

Not silly, your logic is sound but on my car, and probably others, space is tight where the thermostat and the bottom hose meet. To get at mine from above would require removing more parts than it is worth. Going at it from below doesn’t seem safe to me, as you risk getting coolant all over yourself.

Have you looked into adding a T to the highest point in the system? It’s a very common modification.

[moss1972]

Good to hear! I do have the T but I still wonder how that water is going to follow up from the radiator to a closed thermostat if the air has nowhere to go. I don’t particularly feel like drilling a hole in my thermostat plate. I figure some vigorous burping back into the radiator could probably do the trick.

[wetminkey]

Naw,...I've got no special "T" for filling/flushing.
Fill the radiator and cap it. Detach the coolant hose from the passenger's side of the coolant "T", and fill from there, until coolant leaks through the coolant "T". Then fill the last bit through the coolant "T"'s bleeder-bolt, until that is full. Squeeze the upper hoses slightly to 'burp', and top off. Be sure your coolant overflow tank is full and has proper flow to the radiator cap. Open the heater control and warm up the car through a couple of fan cycles. You are done!

[SteinOnkel]

The air bubble always collects at the bottom hose, right in front of the thermostat, keeping it from opening. I've drilled a small hole into my thermostat, it's still a bear to bleed.

Best method I have found is to warm the car up fully, then dump a pot of boiling water over it. Borrow your wife's big ass pasta pot for this.

Then you let it run another few minutes, shut it off and let it cool. Then pop the cap to the radiator and fill it some more. Might have to do this a few times. The design is not stellar, every other car I've owned is much easier to bleed.

[moss1972]

The air bubble always collects at the bottom hose, right in front of the thermostat, keeping it from opening. I've drilled a small hole into my thermostat, it's still a bear to bleed.

Best method I have found is to warm the car up fully, then dump a pot of boiling water over it. Borrow your wife's big ass pasta pot for this.

Then you let it run another few minutes, shut it off and let it cool. Then pop the cap to the radiator and fill it some more. Might have to do this a few times. The design is not stellar, every other car I've owned is much easier to bleed.

Agreed! But forewarned is forearmed. In fact I squished my lower hose last night and it felt like it had air. And the cars running perfectly before I’ve even done the flush and fill.

Thing that makes me wonder the most is that hot water is running from the top line across the Top of the thermostat and back into the block constantly until the thermostat opens. Normally The water in the bottom hose and in the radiator is still cool from the airflow going over them and hasn’t even circulated into the engine yet. So how in the world could the temperature of the air bubble on the bottom of that thermostat have anything to do with how fast it opens? Hot water circulating over the top of it from the block should be enough to heat it. Same principle as the pot of boiling water. Hot water circulating over the top of it from the block should be enough to heat it. Same principle as the pot of boiling water, heat is heat. Plus water has higher thermal conductivity than air. So technically if that bottom hose is full of water and the thermostat has not opened yet then the heat is being stripped off of the thermostat by the water in the hose more so than it would be if they were air in the hose. This is perplexing.

Possibly filling the bottom hose first and then putting a tiny hole in the thermostat might be the best option to cover all bases.

[wetminkey]

Wish I knew what you guys are doing wrong,...
I've never had any trouble getting the air out of my coolant system. And my T-stat does not trap air in the lower hose, as you describe.
I am sure to allow for coolant flow through the heater core as I fill the system,...
Best of luck to you both!

[RRoller123]

Not sure if this helps, but I will post and hope that it does.

[moss1972]

Wish I knew what you guys are doing wrong,...
I've never had any trouble getting the air out of my coolant system. And my T-stat does not trap air in the lower hose, as you describe.
I am sure to allow for coolant flow through the heater core as I fill the system,...
Best of luck to you both!

Well, didn't take long to figure it out. I've read so many daunting posts about problems people have with this process and the nightmares that "fans don't work" afterwards and "thermostats won't open" afterwards it had me paranoid. Then I realized...probably just a shade tree mechanic problem more than a FIAT problem. We figured it out pretty quickly and some cars may be more problematic depending on the condition of their components (water pump, gunk in radiator, clogged tubes, intermittent grounds, etc).

Here is what I learned (video to follow in separate post):

My cooling system was functioning flawlessly before the drain and fill. I expected it to work flawlessly after. Meaning if your fan works and thermostat works before the drain and fill, it damn well should work after. Unless you disturb a temp sensor wire on the bottom of the radiator jacking the car or opening the drain spigot, or you dislodge gunk that clogs the hoses / thermostat / radiator during the drain, flush, fill or whatever you're doing with the system. But plainly speaking, working before = working after.

I jacked the car to get a pan under my oil pan skid grate. Opened 10mm nub on bottom driver side of radiator near the temp sensor to drain radiator. While there I took off temp sensor wires for the fan switch and cleaned terminals. Then I opened the radiator cap, reservoir cap and fill T cap at the high point. Once drained I put the drain nub (plug) back in the bottom of the radiator. [I chose not to drain the block / partial drain and fill]

I filled the system SLOWLY from the T high point until coolant came out the radiator cap. Closed the T. Squeezed a bunch of hoses, got some bubbles but coolant level in radiator did not drop appreciably, covered radiator. Opened bleeding screw (17mm) where coolant flows into the front top of the block, squeezed top hoses along their length, filled up until no more air, put bleeding screw back.

With everything closed up I squeezed the lower hose going from the thermostat, felt full of air. Caveat: before draining the system it felt exactly the same so I proceeded and decided to see what happens. At this point I figured since I was following service manual instructions I would just go for it. Started the car, let it heat up. No fan at 210-220, bottom of radiator coolish, top of radiator hot on drivers side, warmish on passengers side. Bottom hose of radiator to thermostat hose cool on bottom. Determined NO circulation through radiator, just hydro-thermal conduction. Shut car down.

This is where we started getting technical. My first thought went to all the post nightmares about boiling thermostats in water, dumping boiling water over thermostats and breaking out multi meters to frantically hunt down fan problems. I had to laugh because the thermostat was so hot it already felt like it was boiling. Then I said to myself calmly, "working before = working after". We calmly reverse engineered the system (my dad and I) discussing plausible reasons based on the design of the system itself as well as general principles of hydro-dynamics and thermal conductivity. (aka - why all "that crap was hot" and "this crap is kinda warm" but " that lower crap was still coolish")

I determined this...IF YOU READ ANYTHING READ THIS:

The cooling system circulates out of the block, into the thermostat T and back into the top of the block. During this MAIN loop the coolant can also flow off a branch from the rear upper block into the heater core then back to a stem near the water pump if the valve is open (irrelevant to the main system). When the thermostat opens it allows a secondary loop through the radiator to circulate into the system. THIS IS THE KEY. IT ALLOWS IT TO HAPPEN. IT DOESN'T MAKE IT HAPPEN. I think this is where people get derailed into thinking something is broken when its not.

The thermostat opens up ACCESS TO a secondary loop by allowing water to come into the thermostat housing from the hose that comes out of the bottom of the radiator. This is deceiving. How it ACTUALLY works is that the thermostat opens allowing water to come in from the bottom hose BUT water will only come in to the thermostat housing if it's PUSHED into and through the top of the radiator by the water pump.

-----------------------IMPORTANT!!!!-------------------------
Where the large hose goes into the block....it ALSO continues on to the radiator. Just because the thermostat opens this loop does NOT mean it will automatically flow. For instance...if you have a large amount of air in the lower hose it acts like a giant cushion, water in the radiator pushes against, the air pushes back, the water (unable to overcome this resistance) will then TAKE THE PATH OF LEAST RESISTANCE and GO STRAIGHT BACK INTO THE BLOCK (being drawn by the suction of the pump) instead of splitting the flow between the block loop and the radiator loop.

[Physics 101. Air is a fluid. Even though it is less dense than water it behaves the same. The baffles in the thermostat housing increase the resistance required to push the air through thus compensating for difference in density between the two "fluids" in the radiator loop. If its a small amount of air then it will easily overcome but if its too large an air bubble then in essence the hose is already full of "fluid" in the form of air. This prevents the loop from "energizing" and water instead takes a b-line back into the block]

IF YOU HAVE A LARGE AMOUNT OF AIR IN THE LOWER HOSE:
-THE RADIATOR LOOP WILL NOT ACTIVATE WHEN THE THERMOSTAT OPENS
-WATER WILL NOT FLOW THROUGH THE LOOP
-WILL NOT HEAT THE LOWER PORTION OF THE RADIATOR
-WILL NOT BRING COOLER WATER INTO THE BLOCK
-AND (pay attention)
-WILL NOT HEAT UP THE SWITCH TO TURN ON THE FAN

Vis a vis - if your radiator loop aint workin then it LOOKS LIKE you lost your fan AND your thermostat.

The fact is, your thermostat IS LIKELY OPENING just fine but water can't flow through that loop. So this is what we did.

We let the engine cool down, opened the system. Water was present at the bleed screw, radiator cap and T. It was full. I closed the bleed screw and T. Left radiator open. Grabbed the top part of the lower hose and began to "wring" or "squeeze the hose flat and push" the air down the hose and into the radiator. Bubbles came out of the cap and you could hear them moving along through the radiator to the top nicely. It wasn't long before the bottom hose took on a whole new feel. It felt...full. Just to be sure I took the lower hose OFF the thermostat housing and YES IT WAS FULL. Buttoned everything up, topped off radiator and fired up the car.

While the car was running we loosened the clamp on the lower radiator hose where it goes into the thermostat housing and YES WE GOT COOLANT LEAKING so we knew it was full. Moments later steam came off the radiator like mad...we could feel the bottom of the radiator heating up and the fan came on!

Guess what? working before = working after.

IF THE BOTTOM OF YOUR RADIATOR IS COOL BUT THE REST OF YOUR SYSTEM IS "BALLS HOT" THEN YOUR THERMOSTAT AND FAN ARE PROBABLY FINE...the problem is air in your lower hose not allowing the "Radiator Loop" to energize and flow. Just open your radiator cap, take off the hose where the bottom hose coming out of the radiator meets the thermostat, let gravity push coolant from the radiator into the hose, pushing out the air and filling it up, reconnect it to the thermostat, fill the radiator and DONE...system should be full.

I hope this helps some poor schmoe like me later on. As I said full video to follow in another post. As well as a post on heater control valve replacement tips.

Caio bellas!

[SteinOnkel]

Good write-up.

In fact, now that you mention it, the last time I did it I opened up (carefully!) the bottom radiator hose's clamp while the engine was hot and running to let the air out that way.

Couple of question:

"I filled the system SLOWLY from the T high point until coolant came out the radiator cap"

The what now?

"Opened bleeding screw (17mm) where coolant flows into the front top of the block, squeezed top hoses along their length, filled up until no more air, put bleeding screw back."

These cars have bleeder screws? Why am I only hearing about this now lmao.

Oh and I just wanted to point out that thermostats have many more points between "opened" and "closed".

[18Fiatsandcounting]

Steve, thank you, that's quite the epic tome and it will help others. Other than neutron capture cross sections, I think you also covered the scientific aspects as well.

One question from me, as I'm not sure I understood your description of the coolant flow. Here's how I see it:

The water pump moves coolant from the connection at the front of the pump into the engine block, where it cools the block and head before exiting at the T connection at the top front of the cylinder head. When the thermostat is cold, coolant is pumped into the block and upwards through the cylinder head, at which point it hits the T connection. The coolant has 2 choices at this point: It can either go into the upper radiator hose, or it can go through the hose that goes to the thermostat. Since the thermostat is blocked on the side that goes to the lower radiator hose and thus there's a big mass of water sitting in the radiator with nowhere to exit, the coolant goes into the hose that goes to the thermostat, back into the pump, back upwards through the cylinder head, and the cycle repeats. Since this loop doesn't involve the radiator, the coolant comes up to temperature fairly quickly (as designed) but still cools the block and cylinder head.

Now, when the thermostat "opens", the water pump pulls coolant from the lower radiator hose and into the engine block. Upwards it travels to the T-connection, where again the coolant has 2 choices: Either into the upper radiator hose to the radiator, or into the hose that goes back to the thermostat. Since the latter is blocked by the thermostat, the coolant exiting the T connection goes back into the top of the radiator, is cooled on its way to the bottom hose, at which point the coolant is pulled back up again by the water pump. And the band plays on.

Is that how you see it?

-Bryan

[moss1972]

Good write-up.

In fact, now that you mention it, the last time I did it I opened up (carefully!) the bottom radiator hose's clamp while the engine was hot and running to let the air out that way.

Couple of question:

"I filled the system SLOWLY from the T high point until coolant came out the radiator cap"

The what now?

"Opened bleeding screw (17mm) where coolant flows into the front top of the block, squeezed top hoses along their length, filled up until no more air, put bleeding screw back."

These cars have bleeder screws? Why am I only hearing about this now lmao.

Oh and I just wanted to point out that thermostats have many more points between "opened" and "closed".

Check out my video...it walks you through and answers your questions. So as not to be rude of course I will answer them here, I have one of those tees that has a cap on top that you put in the hose at the High Point where the water goes into the heater core at the firewall. This has a little cap on it allows you to fill the system from the High Point.

https://youtu.be/AZtNwm94EbQ

You can see in the video. Also you can see the bleeder screw, it’s 17 mm so it’s not much of a screw as it is a bolt.

Yes I am aware of the thermostats open in stages, ideally smoothly.

Caio!

[moss1972]

Steve, thank you, that's quite the epic tome and it will help others. Other than neutron capture cross sections, I think you also covered the scientific aspects as well.

One question from me, as I'm not sure I understood your description of the coolant flow. Here's how I see it:

The water pump moves coolant from the connection at the front of the pump into the engine block, where it cools the block and head before exiting at the T connection at the top front of the cylinder head. When the thermostat is cold, coolant is pumped into the block and upwards through the cylinder head, at which point it hits the T connection. The coolant has 2 choices at this point: It can either go into the upper radiator hose, or it can go through the hose that goes to the thermostat. Since the thermostat is blocked on the side that goes to the lower radiator hose and thus there's a big mass of water sitting in the radiator with nowhere to exit, the coolant goes into the hose that goes to the thermostat, back into the pump, back upwards through the cylinder head, and the cycle repeats. Since this loop doesn't involve the radiator, the coolant comes up to temperature fairly quickly (as designed) but still cools the block and cylinder head.

Now, when the thermostat "opens", the water pump pulls coolant from the lower radiator hose and into the engine block. Upwards it travels to the T-connection, where again the coolant has 2 choices: Either into the upper radiator hose to the radiator, or into the hose that goes back to the thermostat. Since the latter is blocked by the thermostat, the coolant exiting the T connection goes back into the top of the radiator, is cooled on its way to the bottom hose, at which point the coolant is pulled back up again by the water pump. And the band plays on.

Is that how you see it?

-Bryan

Epic tome. Love it. I had seen a schematic showing water coming out of the lower block to the Tstat and UP into the top of the head. However I think I reversed it now that you mention it. Thank you! Of course it doesn’t change much with how the system behaves it just means my video is wrong. LOL

I will edit the comments thanks again!

[18Fiatsandcounting]

Sounds like a plan, and yes, I'm pretty sure that the water pump pulls coolant into the engine block (where it then flows on up through the head), and the source of that coolant can either be from the lower radiator hose (hot thermostat) or from the hose that connects the T-connection to the thermostat (cold thermostat).

-Bryan

[wetminkey]

Just FYI.
This is from the Fiat Shop Manual:

I hope that helps!
Todd.