Purging air from cooling system with a vacuum pump?

[thefleshrocket]

I installed a tune, spark plugs, MAF, and thermostat in my wife's 2019 Flex Ecoboost. Unsurprisingly, there must still be air in the system because the coolant temp runs at 200-220F at cruising speed (should be a 170F thermostat IIRC) and the heater blows cool at idle. I've followed the FordTechMakuloco how-to for burping the system.

Unfortunately, that hasn't had any significant improvement. I plan to buy a cooling system vacuum pump, but was wondering if I really need to drain the coolant before pulling vacuum on the system and filling it. My thoughts are that if the thermostat is open, I pull a vacuum on the system, and rev the engine to 3500rpm, shouldn't the vacuum help get the air bubble out pretty thoroughly and quickly?

The local Harbor Freight has this tool, which is well-rated and looks to be functionally identical to the one that FordTechMakuloco linked to on Amazon. In addition to being able to pick it up locally, it's about half the price of the Amazon one. https://www.harborfreight.com/cooling-system-test-and-refill-kit-64985.html

 

[Texas Marauder]

Drain the system. You don't have to drain completely, just the radiator and degas tank. Pull a vacuum and use the vacuum to refill. Don't run the engine. Should take less than 2 gallons.

 

[Tbird6]

Once I went to a vacuum filler I never looked back. No trapped air in these modern cars and it's one and done for me. Possibly top up the upper tank a bit after a few heat/cool cycles.

Now it is a bit weird to see all the rubber hoses collapsed with vacuum on them! One tip? Be sure and never let the vacuum run out of fluid when refilling. Otherwise you suck in air and need to start all over.

Wish I had bought one years ago.
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[Shadow351]

Paid $70 for my vacuum coolant fill kit, and it's in the running for best $70 I've ever spent. You can get them cheaper now, it's certainly worth the investment IMO

 

[thefleshrocket]

I bought this vacuum test / fill kit from Harbor Freight and had at it yesterday. https://www.harborfreight.com/cooling-system-test-and-refill-kit-64985.html

Short version, no improvement.

Long version:
--Pulled the Flex into the garage, onto ramps.
--Removed under engine cover, opened radiator petcock, drained into pan.
--Put my mouth onto the reservoir and blew into it to force out any extra coolant.
--Got about a gallon and a half out.
--Hooked up vacuum tool, pulled 26" of vacuum, left it sucking for about 15 minutes.
--Removed air compressor, system held 26" of vacuum.
--Poured coolant through p4nty hose (to filter out particulates) into two empty gallon distilled water containers, one full, one half full.
--Used vacuum fill to suck fluid into system from the full container, maintaining vacuum.
--Vacuum slowly dropped as system was filling.
--Poured the second container into the first one.
--Continued filling.
--Got down to the last inch or so in the container, started sucking air. Reservoir was already above the halfway point, so presumably no big deal.
--Removed tool, poured in last bit of coolant.
--Fired up Flex, let it warm up while idling.
--Coolant temp got to around 160-165F and hovered there. (SCT Livewire.) Sounds good, right?
--Took car for test drive. Coolant temp stayed in same 160-165F range.
--Accelerated briskly to 70-80mph (1/2 to 3/4 throttle, up to ~4500rpm or so). Coolant temp climbed rapidly to around 200F, stayed there.
--When I let off and coasted, the temp dropped 15-20F, into the low 180F range. When I went back to cruising, coolant went back to 200F and hovered there.
--Pulled into a parking lot. Checked heat at idle, was warm but not hot.
--In park, revved to 3500rpm for 30 seconds. Then let idle for 60 seconds.
--Repeated 3 or 4 times, at the end, heat at idle was HOT.
--Drove some more, coolant temp continued to hover around 200F at cruise.
--Came home, hooked up the vacuum fill tool while the engine was idling.
--Had wife rev to 3500rpm for 30 seconds while pulling vacuum.
--Repeated twice.
--Test drive again, no change in coolant behavior.

Is there air still in the system? Is the 160F thermostat "bad"?

 

[thefleshrocket]

I wonder if I have a failed radiator fan. Of the two fans, one works for sure. The other one, I don't know. What temps are the fans supposed to kick on and off? My Flex has an Unleashed tune on it, so presumably different from the factory fan temps.

This morning, 34F, drove the Flex to drop off the kids at school, all in-town driving at light throttle. Coolant hovered around 160F the whole time. Heading out of town, I opened it up and the coolant temp again quicly climbed into the 200F range and hovered there.

Pulling into work, I checked the heat at idle. It's hot, but not HOT. When I rev to 3000RPM, it gets full HOT. So if there's any difference between the heat at idle and at 3000RPM, I assume that means that there's still air in the heater core (and perhaps elsewhere in the system), but how do I get it out? Clearly 15 minutes of pulling 26" of vacuum on the system wasn't enough.

 

[Texas Marauder]

15 minutes of pulling 26" of vacuum on the system is plenty. Just because you have a 160 degree thermostat doesn't mean the coolant will run 160 degrees. It only means that the thermostat opens at 160 degrees. Normally, low fan at @205 degrees, both fans at @215-220 degrees. If you have FORScan or a high level scan tool you can activate the cooling fans to see if they work.

Do you have an auxiliary A/C in the rear? That could make a difference. May need to vacuum longer.

And then there is this procedure.

 

[thefleshrocket]

15 minutes of pulling 26" of vacuum on the system is plenty. Just because you have a 160 degree thermostat doesn't mean the coolant will run 160 degrees. It only means that the thermostat opens at 160 degrees. Normally, low fan at @205 degrees, both fans at @215-220 degrees. If you have FORScan or a high level scan tool you can activate the cooling fans to see if they work.

Do you have an auxiliary A/C in the rear? That could make a difference. May need to vacuum longer.

And then there is this procedure.

I understand that a thermostat's rating is the temperature at which it starts opening, not the temperature that the coolant will necessarily run. What is odd is that if started and left idling, the Flex's coolant temp will stay in the upper 150F range. That doesn't make sense. Though perhaps this 160F thermostat is opening slightly below 160, but even still, since the cooling fans don't kick on until higher, surely the coolant temp should slowly rise above 160.

I used the attached procedure but I didn't do "start engine, rev to 3500 for 30 seconds, idle for 30 seconds, then off for one minute" a total of 10 times. I probably did it about half of that, so that's worth trying again.

Every time I've drained and added coolant, I've had the front of the Flex up on ramps. Could it not being on a flat surface cause problems? Although, even still, I'd think that the purge procedure would still get out the air.

Why would aux AC in the rear matter? My understanding is that there's only one heater core, up front, and that warm air from that is piped back to the rear HVAC.

 

[Texas Marauder]

There is a heater core in the aux A/C. The heater core with the supply lines add volume. I'm just saying that it may require more vacuum time because of the added volume.

 

[kryptto]

were you burping the system with the heat on high?

 

[thefleshrocket]

were you burping the system with the heat on high?

Probably, though I don't remember.

Is there a valve that controls the amount of hot coolant going through the heater core? In my (old school) experience, the heater core is just another radiator that gets a fixed amount of coolant through it regardless of what the heater "lever" is set to--the lever just controls a flapper valve that controls how much air is directed over the heater core (more being hotter) and how much bypasses it (less heat).

 

[kryptto]

turn the cars system up to the highest setting when burping to get the system circulating

 

[thefleshrocket]

I tried again last night, following the instructions in the PDF above. This time with the Flex level on my driveway (IE the front end not up on ramps, like before when I was draining and adding coolant). Coldish start with coolant temp around 100F (car had been driven an hour or so before), rev to 3500 for 30 seconds, idle for 30 seconds, off for one minute, then start and let idle up to operating temp of approximately 175F (when I heard the fan kick on).

Then, 14 times, I set the heat to max (90F and fan to full, front and rear HVAC) and then did:
Start engine, rev to 3500 for 30 seconds, idle for 30 seconds, off for one minute, then repeat. For the last four times, I put it at 3500 for 45 seconds, idled for 45 seconds, and then off for about a minute and 15 seconds. The heat at idle was HOT, like so warm that it was uncomfortable to keep my hand in front of it. I checked the coolant reservoir, and it did not move during the procedure--it was continuously at the "full hot" mark at the seam.

I then drove down the highway at 75mph, and the coolant temp went to upper 190s, per usual, in 30F ambient.

This morning, 15F ambient, my son drove to school with me riding shotgun. In-town driving at light throttle, the coolant temp stayed in the 155-160F range. After dropping off the kids, I drove home. I drive more aggressively, so after one brisk acceleration, the coolant temp was back into the 190s and stayed there until I got to my office. Idling, the temp did start dropping slowly, and was down into the mid 170s after a couple minutes. Air temp from the vents with the HVAC set to 90F and full blast was not nearly as hot as it was the night before, so apparently the air bubble has worked its way back into the heater core.

So in short, all of my bleeding attempts have had no effective change in coolant behavior. In my understanding, with the 160F thermostat, it should start opening around 160F, and be fully open by 170F or so. Cruising at highway speed, the coolant temp should be somewhere between 160F and 175F. At low speeds, in town, the coolant might get hotter, up to around whatever temperature the radiator fan is set to kick up to high speed, probably around 185-190F. (I am assuming that the Flex has a single radiator fan with low and high speed modes, rather than two separate fans.)

At this point, I'm going to ask Unleashed to send me a tune that has the fans set to the stock speeds, and switch back to the stock thermostat, so I can observe its behavior. I am seriously out of ideas of how to purge air from the system.

 

[kryptto]

I tried again last night, following the instructions in the PDF above. This time with the Flex level on my driveway (IE the front end not up on ramps, like before when I was draining and adding coolant). Coldish start with coolant temp around 100F (car had been driven an hour or so before), rev to 3500 for 30 seconds, idle for 30 seconds, off for one minute, then start and let idle up to operating temp of approximately 175F (when I heard the fan kick on).

Then, 14 times, I set the heat to max (90F and fan to full, front and rear HVAC) and then did:
Start engine, rev to 3500 for 30 seconds, idle for 30 seconds, off for one minute, then repeat. For the last four times, I put it at 3500 for 45 seconds, idled for 45 seconds, and then off for about a minute and 15 seconds. The heat at idle was HOT, like so warm that it was uncomfortable to keep my hand in front of it. I checked the coolant reservoir, and it did not move during the procedure--it was continuously at the "full hot" mark at the seam.

I then drove down the highway at 75mph, and the coolant temp went to upper 190s, per usual, in 30F ambient.

This morning, 15F ambient, my son drove to school with me riding shotgun. In-town driving at light throttle, the coolant temp stayed in the 155-160F range. After dropping off the kids, I drove home. I drive more aggressively, so after one brisk acceleration, the coolant temp was back into the 190s and stayed there until I got to my office. Idling, the temp did start dropping slowly, and was down into the mid 170s after a couple minutes. Air temp from the vents with the HVAC set to 90F and full blast was not nearly as hot as it was the night before, so apparently the air bubble has worked its way back into the heater core.

So in short, all of my bleeding attempts have had no effective change in coolant behavior. In my understanding, with the 160F thermostat, it should start opening around 160F, and be fully open by 170F or so. Cruising at highway speed, the coolant temp should be somewhere between 160F and 175F. At low speeds, in town, the coolant might get hotter, up to around whatever temperature the radiator fan is set to kick up to high speed, probably around 185-190F. (I am assuming that the Flex has a single radiator fan with low and high speed modes, rather than two separate fans.)

At this point, I'm going to ask Unleashed to send me a tune that has the fans set to the stock speeds, and switch back to the stock thermostat, so I can observe its behavior. I am seriously out of ideas of how to purge air from the system.

You did what you needed to - however the Tstat companies provide tuners with settings - I believe my Reische did. My tuner - AJP threw them out, looks at my actual numbers and adjusted items as needed. For instance torque converter, wastegate at certain conditions etc. If they aren't explaining the settings ask for more. I am in S Fla so the ambient tps are what they are. All things considered.

 

[thefleshrocket]

I drained the coolant and pulled the Reische thermostat. When I first installed the thermostat, I didn't pay attention to the bleed hole or the rubber gasket. This time when I put it back in, I made sure to put the little bleed hole in the outer edge of the thermostat at the top, 12:00 position. It was slightly to the left of the bleed hole that's in the part of the thermostat that moves; that was at approximately 1:00 with the outer edge bleed hole at 12:00. The Reische thermostat's o-ring wasn't round, it was more triangular and tapered. By which I mean that the outside edge, where it seats against the engine block, is round, and the inside edge is also round, but instead of the whole piece of rubber itself being round, it's tapered. I Googled and couldn't find a firm result, but Google's AI said that the taper should go facing the engine block, so that's what I did. I used my vacuum filler and added a bit over a gallon of fresh orange 50/50 coolant. I then went for a test drive.

NO FRIGGIN' CHANGE.

At this point, I am about 85% sure that the Reische thermostat is just plain bad. I did a ***-of-hot-water test with it and the factory thermostat, which is rated at 180F and the Reische, which is rated at 170F. The Reische started opening at slightly over 160F, and the OEM at slightly over 170F. They were both fully open at approximately 15F higher than their start-opening temps. That seems to make sense. But then I took the *** off of the heat and the Reische took a lot longer to close, like maybe it was partially stuck open. It did eventually close, in the 150s somewhere (I unfortunately didn't monitor it closely enough). I suspect that it is initially sticking open, hence why when I drive gently (IE not putting much heat into the engine), the engine seems to run in the 155-160 range. And then when I do a couple pulls to get more heat into the engine, it seems to stick partially closed, hence why the engine then hangs around the 200-205F range indefinitely after it gets hot.

One other thing worth mentioning--previously, the heat coming out of the vents with the HVAC set to HI and full-blast on the fans, was lukewarm to warm. It would become HOT if I held the revs at 3000+ RPM. Now, after reinstalling the Reische thermostat while being mindful of the bleed holes, the heat coming out at idle with the HVAC on HI and full fans, is now HOT as well. This tells me that I probably did have the thermostat oriented incorrectly, resulting in a persistent air bubble. That air bubble is now resolved, but the thermostat itself still isn't opening properly, because it's probably bad.

Next step is switching back to the OEM thermostat. I bet it behaves perfectly.

 

[kryptto]

Thermostats can go bad for sure. I definately have monitored mine and it opens at or about 170. I run an average of 10 degrees cooler during normal driving. In my heat of S Fla the intercooler can get saturated, far as much a problem now I have GH IC. TBH when I installed my tstat, I don't recall looking over the bleed hole and its direction. I had bought an OEM gasket though and don't recall what I did with the reisch. I have heard of issues with air getting trapped in the system, in various places that a bubble will cause issues., especially the exchanger for heating the cabin. Someone recently posted a repair maunual in these threads. Probably worth a good read. As with any item failure is always an option.

I do appreciate running a bit cooler than stock because of the humidity and heat where I live.

 

[thefleshrocket]

I reinstalled the stock thermostat. I vacuum filled the system, then pulled extra vacuum on it just to be sure. Cruising down the interstate, the coolant temp stays pretty constant in the low 190s, with oil temp in the low 2-teens.

At this point, I am very confident that the Reische 170F thermostat is bad.

 

[kryptto]

Good to hear it's better, thermostats go bad. Will keep an eye on mine now.

 

[BradM]

I reinstalled the stock thermostat. I vacuum filled the system, then pulled extra vacuum on it just to be sure. Cruising down the interstate, the coolant temp stays pretty constant in the low 190s, with oil temp in the low 2-teens.

At this point, I am very confident that the Reische 170F thermostat is bad.

I also did the low temp thermostat install (Even-Flo 160 thermostat LPP2354-160) and have always experienced higher than expected temps and wide fluctuations (you can see the t-stat open and close and bounce between 205-215 cylinder head temp when making hits). My t-stat was oriented correctly and I vacuumed filled the system. I raised this with my tuner and he said "Keep in mind that when logging or looking at PID's the SHO has no coolant temp sensor. The reading is inferred from an algorithm. It does have a cylinder head metal temp sensor. Coolant temps are 10-15 degrees below cylinder head temp" and "But I don't think your cyl head temps should get much over 205 which would be coolant temps around 195 or maybe a touch higher for both".