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coolant not being "sucked" back in

Old 06-14-10, 04:14 PM
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coolant not being "sucked" back in

Hey there track junkies!

I was at Roebling Road last weekend (6/12-6/13) and it was insanely hot & humid, 95+F, plus 90% humidity.

Although I have water injection, the temps would get progressively hotter (almost 245-F), and I noticed that the coolant was getting pushed into the AST (16-lb. cap), and then the coolant reservoir, even while I was idling the car after a 20-minute session for 15-minutes.

I skipped a sessions before lunch allowing the car time to cool down enough to check, and it was low about a gallon of coolant (I run 70% distilled water).

There was only 45-minutes between sessions, so I don't think the car got cool enough to "suck in" the coolant from the reservoir.

Anyone else experience this ?

If so, how do you address this ?

Is this abnormal ?

Do I need to run a water hose to a spigot and aim it a the radiator while it's idling ?

Thanks,
:-) neil

850x4 injectors
stock twin turbos
PFC at 14.2 PSI boost
M2 Medium
Water injection 330cc/min
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Old 06-14-10, 04:32 PM
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flush the system maybe or w/p fail dunno pretty strange
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Old 06-14-10, 06:01 PM
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The system was flushed 2-months ago, and the water-pump is less than 9-months old.

I'm going to get a coolant pressure tester and make sure it holds 16-lbs . . .

:-( neil
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Old 06-14-10, 08:27 PM
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You want a vacuum test, not a pressure test. You already know that under pressure coolant gets pushed out.

One quickie test is to check the vacuum/pressure cap and the lines that run between the cap housing and the expansion tank. On a stock FD, the line between the cap housing and expansion tank is in two pieces connected by a plastic in-line connector. So either line could leak, the connections could leak, or the vacuum cap may not be opening. Strictly speaking, not an exhaustive set of causes, but not uncommon failure points either.

Of course if you've got a non-stock setup between your cap housing and tank, then none of this applies
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Old 06-14-10, 09:06 PM
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Hey Neil!

The expansion/contraction of the cooling system is not related to time at all, it's simply heat and pressure. The more heat, the more pressure, it pushes coolant out, cools and contracts, sucks coolant back in.

Few things to check here -

- The line from the overflow nipple to the overflow tank has to be airtight. A pinhole leak in that line will cause that exact same problem. If it's not airtight, the system can't generate the vacuum to suck the coolant back in.

- Bad radiator cap. Shot in the dark there, but worth checking in to.

- Stuff generally hooked up right. I've seen the AST hoses going to the overflow nipple and vice versa. I doubt you'd do something like that though .

Of course, it could also be a water seal issue, REALLY hope it isn't. Start with the easy things first.

If you have the stock rubber line to the overflow tank, get some 6mm silicone vacuum hose and replace the whole thing. Regular SVH is fine, it is a low pressure hose so it doesn't have to be reinforced and it's compatible with coolant.

Dale
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Old 06-14-10, 10:59 PM
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The last two times this happened to my FC it was the water jacket. (once a failed o ring, once a CRACK next to a spark plug hole!) Good luck

It could be that the tube in the expansion tank is not hooked up correctly and isn't sucking from the bottom of the tank. Dunno how it is on FDs but on FCs its real easy to make that mistake.
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Old 06-15-10, 07:13 AM
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I'll pressure and vacuum check all the hoses.

What other symptoms would indicate a water seal ?

:-) neil
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Old 06-15-10, 10:37 AM
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Originally Posted by M104-AMG View Post
I'll pressure and vacuum check all the hoses.

What other symptoms would indicate a water seal ?

:-) neil
1) coolant light coming on all the time from coolant loss usually because of the slow leak into the combustion chamber.
2) hard starts from wet plugs, running on one rotor until the other is dry
3) runs hot and won't return to normal temp after hard driving
4) when it's near the end lots of coolant smell and smoke along with droplets blowing out of the exhaust
etc....

Good luck neil and hopefully it's not the engine. I have some good engines though if you need one
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Old 06-15-10, 12:39 PM
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Another one for Dales list:

I had a situation on a high-mileage FD whereas the return line was almost completely clogged (at the joining nipple IIRC)....pressure would eject coolant into the reservoir; however, it could not be drawn back into the engine. An easy test: You should be able to blow or suck on the return line with relative ease.



And one for Fritz's "coolant seal" list:

An accumulation of brownish-black crud in the coolant, coolant reservoir, filler neck, on radiator caps, etc.. This residue indicates combustion gases getting into the coolant.
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Old 06-15-10, 04:38 PM
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Originally Posted by Speed of light View Post
Another one for Dales list:

I had a situation on a high-mileage FD whereas the return line was almost completely clogged (at the joining nipple IIRC)....pressure would eject coolant into the reservoir; however, it could not be drawn back into the engine. An easy test: You should be able to blow or suck on the return line with relative ease.
i have seen this too. the symptom is a hose clamp on this hose by the ast. if the hose is clear, then it doesn't come off
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Old 06-15-10, 06:31 PM
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Originally Posted by Fritz Flynn View Post

3) runs hot and won't return to normal temp after hard driving
Running hot and not returning to normal temp only occurred after the third run group (20-minute run groups). No brown/black crud, and she idles great, along with a 18mm Hg vacuum at idle.

I just replaced the line from the coolant recovery/overflow tank to the AST, and I also vacuum (30mm Hg) and pressure tested (20-psi) the old line, and no issues with the old line.

I purchased one of those Lisle Spill-Free Funnels and after filling via the neck (took about a pint), I added another 1/3 of coolant, and started the FD and let her idle until the thermostat opened up.

She pushed out lots of air-bubbles before the thermostat opened, and then once the thermostat opened it seemed like every 3-5 seconds a small air-bubble would surface. Is this normal ?

I then let her cool down for two hours, and the coolant level in the funnel is now half of the 1/3 when I started (1/6).

I'll do this one more time before I got to sleep, and let her sit overnight. I'm also going to get a pressure tester.

FWIW, my aluminum AST is lower than coolant neck, but I though that wasn't a problem.

Hoping its not a coolant seal . . .

:-) neil
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Old 06-16-10, 01:15 PM
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Eventually there should be no air bubbles. How long did you run it for like that?
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Old 06-24-10, 09:48 PM
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The cooling system holds pressure (20-psi) overnight, and the cap tested good, including vacuum.

Here's the issue:

The AST was TOO LOW.

I re-located the AST higher (see attached pic), and everything is good.

In short, the AST needs to be at the same level or higher than the coolant-fill neck. If it is too low, the AST fills-up and cannot "burp" the system/function as it was intended.

That is, when the AST is checked *cool*, the coolant level should be near the same level as the nipple from the coolant-filler neck.

After using the Lisle coolant-filler tool, and going through four (4) burp cycles to purge all air (only 3 cycle per the book, but I needed more with a Fluidyne radiator), I am convinced that the AST is absolutely necessary if you're not using the Lisle tool.

Moreover, the Lisle coolant-filler tool is an AWESOME TOOL and if used must be at the coolant filler neck, not the AST.

:-) neil
Attached Thumbnails coolant not being "sucked" back in-rx7-ast-relocated.jpg   coolant not being "sucked" back in-lisle-coolant-filler-tool.jpg  
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Old 06-25-10, 01:00 AM
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never heard of a problem like this before, what i normally do though, not sure if you do it or not, but I rev the engine to about 2k as I fill it up.
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