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Discussion Starter · #1 ·
Background: New to us 2015 150 xlt 3.7. My best guess is the original pink/orange coolant is still in it, so today I started a series of flush and fills to get it changed over to yellow.

Removed overflow tank lid, removed plastic drain bolt/plug and let it drain. Reinstalled drain bolt, went to pull vacuum on the tank and it won't hold any vacuum past 5 inches.

It's my first time working on this system on this vehicle, so I thought maybe I'd reinstalled the drain plug wrong/crossthreaded/etc. Checked that twice and I'm sure it's fine.

Thought maybe my vacuum puller wasn't working, but just hours before I'd done the same job on my odyssey and it pulled fine. I put it on the empty coolant jug and it crumpled it in three seconds. So I'm not holding vacuum in my system.

However, a few contradictory observations: it was still a little warm when I pulled the cap, and I got a good pressure release hiss. I've got no apparent leaks, and it's held its coolant level in the two weeks we've owned it.

So my questions for you all:
Is there something I'm not thinking about that makes this rig different than other cooling systems? Is there some open end of the system other than the clear overflow/air purge bottle?

Do I have a leak so small it doesn't let fluid out but won't hold a strong vacuum?

Is the leak in some dry part of the system, like the upper line that goes from the plastic bottle back into what looks like the thermostat housing on the front of the engine?

I'm not overheating and I'm not losing coolant, but I'd sure feel better if I could pull a vacuum on it.

Oh, first post here. Great site - I've enjoyed and benefitted from reading all the contributions, and look forward to the interaction.
 

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It's been a long time since I was in the automotive trade, but I'm baffled that you'd be testing the coolant system with vacuum rather than pressure. Coolant system hoses aren't designed for vacuum, and will collapse inward - continuing to slowly do so as the stiff materials yield and distort.

Has something changed in this landscape that I've missed being updated on?
 
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It's been a long time since I was in the automotive trade, but I'm baffled that you'd be testing the coolant system with vacuum rather than pressure.............
I'm lost too. Pressure test it.
 

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Discussion Starter · #4 ·
It's been a long time since I was in the automotive trade, but I'm baffled that you'd be testing the coolant system with vacuum rather than pressure. Coolant system hoses aren't designed for vacuum, and will collapse inward - continuing to slowly do so as the stiff materials yield and distort.

Has something changed in this landscape that I've missed being updated on?
Thanks for the responses. I'd be happy to pressure test it and may do that next - just need to get a pressure tester.
Not to split hairs, but trying to pull a vacuum on the system is technically pressure testing it too, just with a negative pressure instead of positive. Is there a scenario in which it would hold a high pressure test and fail a vacuum test?
Am I correct in thinking the benefit of a positive pressure test is that if it's not holding pressure, you should be able to identify a leak location?
I appreciate the insight of folks who are in the trade. I'm clearly not.
 

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Thanks for the responses. I'd be happy to pressure test it and may do that next - just need to get a pressure tester.
Not to split hairs, but trying to pull a vacuum on the system is technically pressure testing it too, just with a negative pressure instead of positive. Is there a scenario in which it would hold a high pressure test and fail a vacuum test?
Am I correct in thinking the benefit of a positive pressure test is that if it's not holding pressure, you should be able to identify a leak location?
I appreciate the insight of folks who are in the trade. I'm clearly not.
I'm not a physicist, so can't speak intelligently to the difference in this situation between negative and positive pressure relative to atmosphere. But from a practical and mechanical perspective, hoses that are designed for vacuum are rigid and/or have reinforcement preventing them from collapsing. Hoses designed for pressure have reinforcement against bursting but this doesn't necessarily prevent collapse. I'd further speculate that you may even cause damage pulling vacuum on a hose not designed for it, as rigid edges where the flexible tube slides on could actually cut into the tube when it collapses enough. When completely flattened with vacuum, you're causing stress at the two tight folds that aren't anticipated in the design - another potential damage area, or a weakness leading to future failure. Also, the amount the tubes will collapse isn't deterministic. They'll just keep giving slowly, which will skew your test results.

And yes, you raise a good point that pressure can help pinpoint leaks. Often a UV dye and light are used to make this even easier.
 

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What was the engine temp. When I was a master tech for BMW the shop I used to work at had a machine that used vacuum to remove the coolant. It was very efficient and flushing the old coolant out was not needed so less waste. We would warm up the engine then shut the engine off then suck the the coolant out. It would go into a vacuum that the coolant would boil and almost all the coolant would be evacuated quickly because the boiling coolant would flush the coolant out. Then he vacuum would suck the new coolant in and the flushing of the system only took a couple of minutes and we did it all from the reservoir fill.

So basically if the engine still had any heat and any coolant still in the engine you won’t be able to get as low of a vacuum because the coolant will be boiling at a vacuum pressure that is closer to atmospheric pressure.
But yeah only leak test AC systems with vacuum, pressure test cooling systems
 

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I spent many years bent over engines but I'm not claiming to be a expert on how Ford designed every seal and gasket on the Transit cooling system. I can say, with some confidence, the purpose of all those seals/gaskets is to keep the coolant in the system and not to keep atmospheric pressure out. The system normally operates under pressure, therefore testing it in a vacuum, may result in a false leak detected. Also, how are you going to locate any leak(s) if all your test is doing is letting air into the system? You can't see air going in but if you pressure test it, the coolant will come out someplace and you should (might) be able to see where it's coming from (if it's not a internal leak). A qualified auto shop should be able to diagnose the leak location somewhat quickly. I'd first do a simple pressure test, followed by a check for hydrocarbons in the coolant. There's a tool that you use to do that. It uses a fluid that changes color if there are hydrocarbons in the coolant. If hydrocarbons are present, then combustion gases are getting into the coolant. That result would indicate a "probable" head gasket failure and require further investigation, such as removing spark plugs while pressure to see if coolant gets into any cylinder(s). Many mechanics want to "jump the gun" and remove the head(s) before pinpointing the affected cylinder(s). I always removed the plugs and tested the system before filling the workbench with removed parts. That way you know where to look when the head is removed. Hopefully your vehicle has a simple loose clamp someplace that's easy to get to but Mechanics do have to eat too LOL!
 

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I'm a Ford senior master tech and may be able to clarify some things here.

Guys in our quick lane use a vacuum filling system in order to fill the cooling system quickly and effectively without introducing air into the system. This process in theory allows them to fill the cooling system without having to then go drive the vehicle and burp the air out, because when they introduced coolant into the system there was no air or very little.

I absolutely never ever use vacuum filling apparatus for filling cooling systems.

Why?

I have seen many a vehicle roll into the quick lane, get sold a cooling system flush, techs suck out the old coolant, vacuum fill the new cooling system with new coolant and send the vehicle on its way. Several minuets or hours later, that customer returns with a vehicle leaking coolant.

What happened?

As others have stated above, the system is designed to hold coolant in the system, not keep atmospheric pressure out. There is one seal in particular that usually fails when placing extreme vacuum on the cooling system. That would be the shaft seal on the water pump. Often times on older water pumps when a large amount of vacuum is placed on it, the seal will fail. Most of the time is slight, the tech fills the cooling system, parks the vehicle and walks away. Customer gets in, and soon they are running out of coolant and their engine is overheating or making a mess on their driveway. Sometimes after applying vacuum the cooling system will just immediately puke coolant out, this will be noticed very obviously.

In your case, I'm wondering if you have damaged that seal by applying vacuum to the cooling system, maybe that seal has completely torn or been sucked inwards and now the system can not maintain vacuum. This would explain why previously the vehicle was not leaking and now it can't maintain vacuum.

My opinion, if you want to change coolant over, drain out the old coolant. Fill the system with water, run the engine for five minuets. Drain the cooling system again and then fill it with the new coolant. An old water pump that could get damaged by vacuum filling could easily go another 50k miles before needing to be replaced, you never know if your water pump is sensitive to damage from vacuum.

I would add water to your engine, put the cooling system cap on and run the engine until the vehicle starts to build cooling system pressure (or is incapable of doing so) and see where the water leaks out, I would bet its going to leak from the water pump weep hole.
 

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Discussion Starter · #9 ·
I'm a Ford senior master tech and may be able to clarify some things here.

Guys in our quick lane use a vacuum filling system in order to fill the cooling system quickly and effectively without introducing air into the system. This process in theory allows them to fill the cooling system without having to then go drive the vehicle and burp the air out, because when they introduced coolant into the system there was no air or very little.

I absolutely never ever use vacuum filling apparatus for filling cooling systems.

Why?

I have seen many a vehicle roll into the quick lane, get sold a cooling system flush, techs suck out the old coolant, vacuum fill the new cooling system with new coolant and send the vehicle on its way. Several minuets or hours later, that customer returns with a vehicle leaking coolant.

What happened?

As others have stated above, the system is designed to hold coolant in the system, not keep atmospheric pressure out. There is one seal in particular that usually fails when placing extreme vacuum on the cooling system. That would be the shaft seal on the water pump. Often times on older water pumps when a large amount of vacuum is placed on it, the seal will fail. Most of the time is slight, the tech fills the cooling system, parks the vehicle and walks away. Customer gets in, and soon they are running out of coolant and their engine is overheating or making a mess on their driveway. Sometimes after applying vacuum the cooling system will just immediately puke coolant out, this will be noticed very obviously.

In your case, I'm wondering if you have damaged that seal by applying vacuum to the cooling system, maybe that seal has completely torn or been sucked inwards and now the system can not maintain vacuum. This would explain why previously the vehicle was not leaking and now it can't maintain vacuum.

My opinion, if you want to change coolant over, drain out the old coolant. Fill the system with water, run the engine for five minuets. Drain the cooling system again and then fill it with the new coolant. An old water pump that could get damaged by vacuum filling could easily go another 50k miles before needing to be replaced, you never know if your water pump is sensitive to damage from vacuum.

I would add water to your engine, put the cooling system cap on and run the engine until the vehicle starts to build cooling system pressure (or is incapable of doing so) and see where the water leaks out, I would bet its going to leak from the water pump weep hole.
Thanks alex, I appreciate this insight, too. I've digested these responses and have decided to get rid of the vacuum pump, continue to just do my standard drain/fill/top off that has always worked for me, and in the meantime get a pressure tester to see how it holds up. At 112k I'm probably starting to feel like changing the water pump and timing belt anyway, as well as maybe plugs if the manifold is out. I'll take a look around the pump weep hole (once I find it) next to see how it looks.
 

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I drained my coolant and added a rear heater and then assembled and filled with coolant , then while parked rev the RPM up I think it was at 3000 RPM for 60 seconds and then go under hood and remove radiator cap to bleed out air , I think I repeated this procedure a couple of times if I remember correctly.
Worked out well.
Also after driving for a bit you could stop and remove your cap to release psi
It doesn't take long to get the air out
This procedure I found on Youtube
 

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Thanks alex, I appreciate this insight, too. I've digested these responses and have decided to get rid of the vacuum pump, continue to just do my standard drain/fill/top off that has always worked for me, and in the meantime get a pressure tester to see how it holds up. At 112k I'm probably starting to feel like changing the water pump and timing belt anyway, as well as maybe plugs if the manifold is out. I'll take a look around the pump weep hole (once I find it) next to see how it looks.
Always happy to be of assistance! If you are considering replacing the accessory drive belt at this mileage, that makes sense to me, but be aware your vehicle does not have a timing belt. It has a timing chain that doesn't require servicing. Hopefully your able to track down an issue with the car, or better yet, hopefully you fill her up with coolant and find no issue at all!!
 
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