Sucking air???

[Dan Sarandrea (Phila)]

You can see in your pic in the design of the header that there was a conscious effort to route the tubing so that (1) it could be equal-length yet (2) clear an A/C compressor.

I can certainly understand that a shop doing a low-volume custom item would want to make one design that would fit both A/C and non-A/C cars, but in retrospect that might have been a bad call if indeed the design does create the type of problem that you are experiencing.

I think the good news is that it should be relatively easy for a competent welder to make up a water pipe that can be routed away from the header. Even a crazy looking U-shaped path that would have the 90 degree bypass hose point straight down, go down well under the header, go horizontal for 1-1/2 feet, then 90 degree up and then 90 degree into the pump. Heck, you could probably use some ready made, generic exhaust pipe pieces and generic flexible coolant hose from the local auto part store to make a temporary pipe assy to test your theory.

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[lookforjoe]

Yes I purchased the version with ceramic coating. My prior concern which I think is now verified by the mechanic is that two of the header tubes are VERY close to the water pipe. One is ~1/4", the other is perhaps 1/2" but also runs along the length of the water pipe. The link below shows some photos from the original install two years ago (uh, right before I realized I had an air problem) where you can get a feel for the issue:

Would be curious to hear from other Allisons header owners. Keep in mind the design changed over time. I don't think the original design ran the passenger side tubes so close to the heat pipe. This change was made later when they re-routed the tubes so they'd no longer block injector shroud ducting (a problem with the first gen design). Pretty sure my header was one of the first of the modified versions.

I have had the same issue with mine - I bought an early one also. Mine was less than 1/8" off the heater / return pipe.

This is what I did to mine after I realised it was an issue

However, that was not enough.

I tweaked it further when I did the motor build.

When I had the motor apart (again) this last time, I decided to stick a pry bar in it and bent it back away from the header, closer to the motor. Now, I have REAL clearance No pic, though.

I would be hestitant to fabricate convuluted piping, just bend it back on an angle closer to the block at the T/stat end. You may need to check the elbow hose fitment after, and I would certainly closely inspect that pipe for structural integrity before bending it - mine had a fair amount of surface rust pocketing, but the wall thickness is still good, so I didn't worry too much about stressing it.

Wrapping the pipie with any that will reduce the air gap when it's already close is also a bad idea, IMO.

 

[geekdaddy]

Dan/Hussein -- thanks for the recommendations. Hussein: My header is a revision made after yours. In my rev, there are TWO exhaust runners which nearly touch the pipe. But I may try something similar to your approach. Dan: Unfortunately there's no room for a "u-shape" approach. The header actually wraps around the water pipe so the area below the water pipe is even worse (the header tubes and collector bend closer to the block).

The best option I have is to bend the water pipe (or fabricate a new one) so it bends very close to the block and then if possible build a thin heat shield to fit between the pipe and the header tubes. Will do further research...

 

[geekdaddy]

Victory is mine!!!

After over TWO years of troubleshooting this the problem is resolved!!! Unfortunately I'm not entirely certain if one or both of the following mods resolved it:
1. Insulated allison's header and shielded water pump and pipe.
2. Filled overflow tank to within an inch of the filler neck.

After doing a lot of temp testing I knew that two header tubes were too close (less than 1/4") to the water pump and pipe. The header temp measured over 500 degrees and the water pump/pipe was over 280 degrees. I had the pipe modified to route it closer to the engine block and further from the header. This gave me just under an inch to insulate and shield the water pipe. IR temp measurements at the pump and pipe are now under 200 degrees behind the shield -- perhaps a little cooler under the insulation.

I also noticed that my metal tank "pees" coolant from nearly the top of the tank. At high rpms the stream is very fast, turbulates the coolant and causes air bubbles which are momentarily pushed to the bottom of the tank where the return lines are. I normally filled my tank to ~3/4 height but have now topped it to within an inch of the top. So now the coolant stream directly hits the coolant without passing thru an air gap -- no bubbles.

Since I shielded the header heat and filled the tank at the same time, I'm uncertain which was the primary culprit. My suspicion is the air may have been ingested by the lower coolant height in the tank but the unsteady temperatures exacerbated by the boiling coolant in the water pump tube due to header heat. After 300 miles of driving the temps are now rock steady on highway, back roads, stop/go traffic and idling in the driveway after a hard run. Radiator fans come on as-expected during long idles (30 mins) in the driveway or stop/go traffic and the system can cool itself. No air in the radiator.

My advice to others with an allisons header is to measure your engine compartment temps -- especially near your coolant pump and pipe. There are a few different revisions of the header which route the tubes more or less around the water pump pipe -- my rev (early 2014) has one exhaust tube that runs 1/4" along nearly half the length of the water pipe. I believe this change in header tube routing was made so the header would not block injector cooling shroud. Anyhow -- yours may be slightly different but worth checking.

 

[Black-Tooth]

Congrats... and hopefully this cures all.

What a nosebleed!

 

[lookforjoe]

Good to hear you have resolved the issue!

I reverted to the plastic tank, to address the volume of turbulence created by the high return of the SS tank, that just seems like a bad design. I also keep the tank over 3/4 full , cold.

 

[lookforjoe]

Any additional updates? Have you put more miles on it?

I found an old pic I took showing the proximity of the branch pipe from underneath on my version Allison header.

After your observations and back & forth with the branch pipe / header setup, I made a replacement branch pipe for my setup.

 

[geekdaddy]

All is well! Since adding the heatshields and re-routed water pipe all the engine temps are much cooler. No issues any more. I've been driving all over the place and hammering the little 1.5L pretty hard.

Any additional updates? Have you put more miles on it?

I found an old pic I took showing the proximity of the branch pipe from underneath on my version Allison header.

After your observations and back & forth with the branch pipe / header setup, I made a replacement branch pipe for my setup.

 

[JimD]

That is good news

I haven't added to this conversation since I didn't have any idea how to help, but I know good news when I hear it!! Congrats! :thumbsup:

 

[geekdaddy]

UPDATE: I've verified after driving last season and the start of this one that I am still experiencing some air in the radiator. With all the changes discussed here (insulating the coolant pipes from header heat and filling the overflow tank to a very high level) the rate of air build-up is substantially less. I previously had to bleed my radiator every 100-150 miles just recently noticed some air again after ~2K miles. I know when there's air in the radiator because when there's NO air the temp guage is rock-steady across all conditions. When air starts to build the guage will rise slightly on spirited runs and then return back to midline later. I've installed a different coolant tank to see if that will eliminate or further reduce the issue.

 

[Mxgrds]

I experience the same issue, first with a FI 1500 engine and now with a UNO Turbo 1.3 engine. Have followed a lot of the suggestions here, even replaced a headgasket twice. Still the same problem. Both engine drives very well and no cooling fluid leakage. I gave up and made it easy to easy for myself to de-air the radiotor by extending the de-air plug on the radiator. Every time I put the roof in te frunk I just de-air the system.

I was wondering. The problem is that the air is trapped in the top of the radiator because the outlet of the radiator is on the bottom. Air arriving in the radiator will not be sucked out because it will not be pushed down. Will it help to make a small passage (break pipe) from the bleed screw (which is a the top) to the bottom of the return hose. So that air can be sucked back to the reservoir? A passage wide enough for air but small enough for not letting through a whole lot of hot coolant? I was hoping that the pressure will push the air up into the bleed screw passage and then into the return hose. An self-air-bleeding mechanism, so to say.

 

[kmead]

Perhaps adapting something like these units would work instead?

https://www.plumbingsupply.com/aireliminators.html

Air eliminator are used in hydronic heating systems all the time and can work continuously.

 

[Mxgrds]

Perhaps adapting something like these units would work instead?

https://www.plumbingsupply.com/aireliminators.html

Air eliminator are used in hydronic heating systems all the time and can work continuously.

Not enough room to install. Need to stand straight up. Also not useable for moving car.

 

[ecohen2]

This thread has been super interesting and I should have paid more attention to it earlier. Ill add a couple of items that I recently learned while tracking down air leaks etc.

* I found a couple of air leaks by heating up the car, turning my garage lights out then shining a bright LED flashlight along the radiator, hoses etc. None of these leaks were visible with the flashlight and the garage lights on...

* The Vicks radiator works great but I did have a leak where the bleeder valve goes into the radiator. I replaced the copper crush washer a couple of times but could not eliminate the problem. I then put some anti-seize compound on the thread and have not had an issue in several hundred miles. Just a note, I did the same thing with my transmission drain plug and stopped the oil weeping..

* When air gets into the system I seem to get a bubble either near the water pump or in the heater core. I have not had any issues with air in the radiator since I put the anti-seize compound on it. The symptom of this bubble is the engine temp goes way high for no apparent reason, like cruising at 65 mph when it is in the low 80s outside. I accidentally discovered that if I turn the heat on for about 45 second and then turn it off again the bubble moves away. Of course the temperature drops way down almost immediately, but then I see it behave correctly on the highway and stays at or below 190..

* I do see the bubbles generated by the return feed into the expansion tank. Has anyone thought about just inserting a tube so the coolant return exits into the fluid instead of drizzling into it? This would reduce the amount of bubbles in the tank.

* Lastly, I have not figured out what changed the color of the coolant but I am just driving the car until something becomes obvious. I wonder if two different brands of "green" coolant are incompatible and that has made it turn milky?

Ed

 

[lookforjoe]

Not enough room to install. Need to stand straight up. Also not useable for moving car.

I wouldn't make a convoluted bleed system - it shouldn't need it if the system is properly bled & free of leaks and /or seepage points. I've tried various add in / supplements to the system over time, and they all just add potential leakage points. Keeping it as simple as possible and as close to original configuration (if enhanced) seems best in my experience.

Even a slightly loose clamp on any one of the fittings or hoses will allow air to be sucked in to the system. Once you have eliminated all sources of external leakage (took me many tries to find and fix all, then new ones develop as hoses age harden, etc...) then a few bleeds at the radiator will eliminate any air left. If it does not, you still have air being drawn in somewhere in the system.

 

[geekdaddy]

There can be several causes of air intrusion in our exxies. A few have more obvious root-causes and fixes:
1. Head gasket failure. You should find coolant in oil (or vice versa) or detect exhaust gases in the overflow tank (this can be tested).
2. Fittings, hoses, etc connected to the radiator, thermostat, head, heater, or coolant tubes that are leaking. System can be pressure tested and leaks visually identified. ...or use marker fluid to make it easier.

In my case there were two add'l issues which caused air intrusion and are related to "non-stock" items on my engine:
1. Allison header was overheating my water pipe. Still not certain this caused air in the radiator but was definitely causing cooling system problems.
2. Stainless overflow tank. Return line "pees" down into tank. At high RPMs this turbulates water and pushes air into the bottom of the tank. The air is sucked into the overflow exit hose at the bottom, travels to the radiator, and some of the air rises to the top of the radiator and is trapped there during cooling.

I suspect many others using the stock stainless or repro stainless tanks may experience this problem over time -- especially with spirited accelerations where RPMs run high. If you look at the stock plastic tank the return line travels across the top of the tank (not down) and is less susceptible to this issue. The stainless design is different and CAN work better if coolant level is VERY high in the tank. This allows for little or no air gap between the return line output and top of coolant to draw in air/bubbles.

I had success with the original plastic tank and have had success with the Vick's aluminum tank. An ideal scenario would be a tank like Vick's aluminum which also has 1-2 small internal baffles to discourage air bubbles from finding their way to the bottom of the tank. It's a remote possibility with the current design but would be near-impossible with horizontal or angled internal baffles.

Hope this helps others!

 

[autox19]

There can be several causes of air intrusion in our exxies. A few have more obvious root-causes and fixes:
1. Head gasket failure. You should find coolant in oil (or vice versa) or detect exhaust gases in the overflow tank (this can be tested).
2. Fittings, hoses, etc connected to the radiator, thermostat, head, heater, or coolant tubes that are leaking. System can be pressure tested and leaks visually identified. ...or use marker fluid to make it easier.

In my case there were two add'l issues which caused air intrusion and are related to "non-stock" items on my engine:
1. Allison header was overheating my water pipe. Still not certain this caused air in the radiator but was definitely causing cooling system problems.
2. Stainless overflow tank. Return line "pees" down into tank. At high RPMs this turbulates water and pushes air into the bottom of the tank. The air is sucked into the overflow exit hose at the bottom, travels to the radiator, and some of the air rises to the top of the radiator and is trapped there during cooling.

I suspect many others using the stock stainless or repro stainless tanks may experience this problem over time -- especially with spirited accelerations where RPMs run high. If you look at the stock plastic tank the return line travels across the top of the tank (not down) and is less susceptible to this issue. The stainless design is different and CAN work better if coolant level is VERY high in the tank. This allows for little or no air gap between the return line output and top of coolant to draw in air/bubbles.

I had success with the original plastic tank and have had success with the Vick's aluminum tank. An ideal scenario would be a tank like Vick's aluminum which also has 1-2 small internal baffles to discourage air bubbles from finding their way to the bottom of the tank. It's a remote possibility with the current design but would be near-impossible with horizontal or angled internal baffles.

Hope this helps others!

interesting. This might even help my issue! good part, it will be easy to test with pinch off clamps to slow the coolant to the overflow.

Odie

 

[Mxgrds]

Return line 'pees' into stainless steel tank. On my turbo i have also the return from the turbo joined with the return from the thermostat. Double bubble feast in the tank. I will try to fill the tank up to almost full.

 

[Mxgrds]

Definitely not a head gasket leak. But a lot of bubbles in the reservoir. See this
https://goo.gl/photos/C1u56v6tqEVuiU3n8

I suspect the return water from the turbo to cause this. The returnline is much hotter than the line from the thermostat. And the hotter the more bubbles I suspect. Not difficult to assume the bubbles will be drown into the engine again.

 

[Dan Sarandrea (Phila)]

While bubbles are interesting, keep in mind that in operation with the cap on, system pressure will be somewhere in the range of 0 psi all the way up to the blow-off pressure of your cap. OEM caps are rated for about 11 psi but most aftermarket caps are rated at 13 psi. With the cap on system pressures at cold engine startup will be 0. As the coolant heats and expands, air in the expansion tank will be compressed, thus creating system pressure. It is reasonable to assume that bubbles generated by the agitation of the coolant as it returns back to the expansion tank will be lessened to some degree, or maybe eliminated by the pressure. It would be interesting if there were a clear expansion tank that could be fitted to examine whether or not that's a good assumption.