Cooling System Pressure Test
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HT4100 4.1, 4.5, 4.9 Discussion, Cooling System Pressure Test in Cadillac Engine Technical Discussion; Had to do some work on the power steering rack (adjusting the bearing preload). Jacked up the front of the ...
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    ckucia is offline Cadillac Owners Fanatic
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    Cooling System Pressure Test

    Had to do some work on the power steering rack (adjusting the bearing preload). Jacked up the front of the car ('89 Allante 4.5) to get underneath.

    After awhile when I was under there, coolant started dripping on my head.

    Unfortunately, as I had driven the car fairly recently in the rain, pretty much everything under there was wet and I couldn't trace the leak. I did find a little puddle of coolant in the little well behind the top large bolt on the LH side (back) of the water pump.

    So, I bought a cooling system pressure tester - I wanted one anyhow.

    Pressurized the system to 16psi while cold. No leaks and no hissing anywhere.

    Warmed up the engine. No leaks - no hissing.

    Gave it a few days rest.

    Yesterday, I sprayed brake parts cleaner all over the side of the block around the water pump, and the back of the block and over everything that was wet to clean/dry it off. Made sure the coolant was up to the pressure cap on the radiator and the surge tank was filled.

    Pressure tested it again - no leaks.

    Ran the car till it was fully warmed up - no leaks.

    Jacked up the front of the car - no leaks.

    I even tried bumping the pressure up to 32psi. Still couldn't get a leak.

    One thing though is that the pressure doesn't hold. It will drop about 1psi every 10 minutes or so. I can't say if this is due to a leak in the cooling system, or just internal to my tester - its the first vehicle I've used it on. Should the cooling system hold pressure for a long period of time?

    This is driving me batty. Since I can't get it to leak, I'm inclined to start driving it again and just watch carefully. Also verified the surge tank isn't leaking, although I didn't pressure test it.

    Any ideas?

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    BeelzeBob's Avatar
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    Re: Cooling System Pressure Test

    Quote Originally Posted by ckucia
    Had to do some work on the power steering rack (adjusting the bearing preload). Jacked up the front of the car ('89 Allante 4.5) to get underneath.

    After awhile when I was under there, coolant started dripping on my head.

    Unfortunately, as I had driven the car fairly recently in the rain, pretty much everything under there was wet and I couldn't trace the leak. I did find a little puddle of coolant in the little well behind the top large bolt on the LH side (back) of the water pump.

    So, I bought a cooling system pressure tester - I wanted one anyhow.

    Pressurized the system to 16psi while cold. No leaks and no hissing anywhere.

    Warmed up the engine. No leaks - no hissing.

    Gave it a few days rest.

    Yesterday, I sprayed brake parts cleaner all over the side of the block around the water pump, and the back of the block and over everything that was wet to clean/dry it off. Made sure the coolant was up to the pressure cap on the radiator and the surge tank was filled.

    Pressure tested it again - no leaks.

    Ran the car till it was fully warmed up - no leaks.

    Jacked up the front of the car - no leaks.

    I even tried bumping the pressure up to 32psi. Still couldn't get a leak.

    One thing though is that the pressure doesn't hold. It will drop about 1psi every 10 minutes or so. I can't say if this is due to a leak in the cooling system, or just internal to my tester - its the first vehicle I've used it on. Should the cooling system hold pressure for a long period of time?

    This is driving me batty. Since I can't get it to leak, I'm inclined to start driving it again and just watch carefully. Also verified the surge tank isn't leaking, although I didn't pressure test it.

    Any ideas?
    You don't have a "surge" tank on the 4.5 Allante. The Northstar uses a pressurized surge tank in the cooling system but the system in the 4.5 is a simle coolant recovery bottle. It is under no pressure per se. The pressure cap is on the radiator on the 4.5 so the system is pressurized from there and the coolant recovery bottle just traps the overflow and refills the system as it cools and a vaccum is created in the cooling system.

    The cooling system should hold pressure for a long period of time. Can't you dead head the cooling system pressure tester and pump it up and see if the tool is leaking...???

    Lots of times leaks are hard to find with a pressure checker. Pump it up cold and leave the pressure on the system for several hours. Coolant actually leaks fairly slowly thru most small leaks, especially when cold. You can do a "better" leak check by draining the system and pumping it up to pressure empty...the air in the system will leak thru any orifice "easier" and you can determine thru the pressure decay if there is a leak and/or hear it easier as the leak will be magnified by just leaking air. Figure out if your pressure checker is leaking first though. You might want to put a pressure check valve in the hose from the tool to hold the pressure better.


    It is NOT a good idea to pump the system up to more than 15-18 PSI. The radiator and heater core can be damaged at higher pressures. The flat tubes in the radiator and heater core will tend towards going "round" when subjected to higher pressures and can crack and/or deform the fins that are between the tubes. It is common to see older radiators loose cooling efficiency after subjected to even a severe overheat/high system pressure as the pressure deforms the tubes and can actually crack the solder joints between the tubes and fins. The engine will not be hurt by the higher pressure at all....but the rad and heater core definitely do NOT like pressures higher than 18 PSI....!!!


    Are you running the GM Coolant Supplement/BarsLeaks "golden seal" in the sytem?? That should seal up any tiny leaks like you describe.

    The best thing to do , after making sure that there are no obvious leaks (like you did with the pressure check of the full system), is to fill the sytem/install the sealer and fill the coolant recovery bottle, thermal cycle the system a few times to make sure the system is purged of air and then mark the coolant level when COLD on the coolant recovery bottle and watch the coolant level over time to see if it drops.

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    ckucia is offline Cadillac Owners Fanatic
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    Re: Cooling System Pressure Test

    Thanks for the info.

    Sorry about the confusion on my end on the terminology.

    The pressure tester I have uses a bladder to seal in the radiator cap port. I guess I could stick it in a 2-liter soda bottle and see if it will hold the pressure.

    Emptying the system is a good idea. I guess I made leak detection more difficult by making sure the system was full of fluid.

    I am using the cooling system supplements.

    I'll post more when I have more info. Hopefully I'll get to it tonight.



    I do have another question that occured to me when I was working on the car. When you first put coolant in the system, presumably there is air in it. How does the air get out? Seems like the radiator cap is at the high point of the system and the radiator cap seems to be the only means for anything to get in or out, but I don't understand how the cap can release air while still holding the system pressure and/or letting coolant in.

    Or is a certain small amount of air acceptable in the radiator as long as coolant is flowing in and out?

    My best guess is that any air in there expands and gets released by the pressure cap and bubbles out the overflow tank, but that's just a guess.

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    Re: Cooling System Pressure Test

    The Internet is a wonderful thing:

    http://auto.howstuffworks.com/cooling-system7.htm

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    Re: Cooling System Pressure Test

    Part of the answer is that the design of the cooling system is such that air will purge out of it. That is an important consideration in designing and plumbing the cooling system in any car....that is why you sometimes see vent lines and vent ports in the system. The 4.x engines eliminate air pockets very easily. Any air trapped in the sytem is "flushed" to the radiator where it vents out the cap as the system heats up and builds pressure. If you look at the plumbing of the coolant recovery bottle the line from the cap goes to the bottom of the bottle below the coolant level in the bottle. So...any air that vents escapes thru the coolant in the bottle and as the system cools then it pulls coolant back in. That is why you want to fill the rad and the bottle and then go thru several warm-up/cool-down thermal-cycles with the engine/cooling system to make sure all the air is out. Then refill the coolant recovery bottle and mark the level for reference.

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    Re: Cooling System Pressure Test

    I did a little more work last night. Drained the system and pressurized it.

    I did find a couple of hissing hoses. Nowhere near the leak, but they're tight now.

    I think I have some hissing near the back of the engine. Unfortunately, it is so faint, and my neighborhood is so noisy at night, that I couldn't locate it. It may not even be where I think it is, or I may have been imagining it!

    I went around and tightened all the hoses anyhow and verified the water pump fasteners are all tight.

    It got too cold last night to play around with it anymore. I'll try again tonight.

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    ckucia is offline Cadillac Owners Fanatic
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    Re: Cooling System Pressure Test

    Worked more on this last night.

    I did find a couple more hissing hoses. One was the back end of the hose that wraps around the back of the block behind the water neck. It was the only hissing hose that actually had signs of leaking.

    However, none of the hoses that I found hissing totally explain the coolant I found, which had dripped onto the cradle by the harmonic balancer, and run back towards the mounts. I think what dripped on my head was from the leaking hose on the back of the block though, and since the balancer is below the coolant recovery bottle, I suppose it could have spilled when I filled it last - its been too cold here in Cleveland for it to evaporate.

    Anyhow, after tightening everything up, I pressurized it to a little over 15psi and it held pretty consistently, losing maybe 1/10th of a psi over the course of 1/2 an hour. At that rate, I can't identify any further leakage so I filled it up again. I'm going to watch it carefully once I start driving it.

    Unfortunately, I'm not driving it yet because I still have a "clunk" in the steering. I replaced an inner tie rod end. Couldn't get to the other side and it seemed OK. Its driving me crazy. Going to enlist the help of my girlfriend tonight to help me locate it.

    The weird thing is I can only get the clunk to happen when the engine is running and running the power steering. Then, if I move the wheel back and forth, there's a clunk in both directions. If I put my foot on the brake, I can feel it through the brake pedal. Without the engine running, and with the wheels on the ground, its almost impossible to duplicate. Also difficult with the wheels off the ground. Going to see if I can jack it up high enough that I can get in there, but still keep the wheels on the ground. I could probably still drive it, but I'd prefer to at least know where its coming from first.

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    Re: Cooling System Pressure Test

    Argh!

    Took the car out for a drive last night. Ran out of coolant supplements so I'm heading out today to get some.

    Anyhow, coolant was all over the top of the intake manifold, under the alternator, on the side of the engine above the waterpump and back along the side of the head. Nothing on the valve covers, overflow tank, top of the distributor or ps pump, or anywhere on the RH side of the manifold (by the water neck). Also, the hood pad was dry as were all the hoses by the strut tower.

    About the only thing I can figure is that the far (LH or back) side of the water pump gasket is leaking and squirting upwards enough that its getting up to the intake and running down, but not high enough to hit the hood pad. I watched the engine while running, and couldn't see anything coming out, but everything's wet.

    Does it make sense that, if the system is operating at 15psi (based on the cap) that the pressure aft of the water pump impeller is much higher in order to pump coolant, especially at high rpms? Where I suspect I'm getting leakage is where the water pump enters the back of the block where the rear head is. Seems like that would be a high-pressure area and might not have leaked with my pressure tester?

    I guess its also possible the timing cover gasket is leaking. If I remember, the timing cover is like a sandwich: block + gasket + timing cover + gasket + water pump. I can't see any of the other gaskets/hoses in the area leaking and depositing coolant where I'm seeing it.

    Running out to get a bunch more coolant supplements at lunch. Maybe that will stop it up.

    Sure wish I could positively identify this. I think i'm gonig to try getting it hot and revving the engine to see if I can get the leak to show itself. Don't know what else to do.

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    Re: Cooling System Pressure Test

    Isn't there a steel pipe that transfers the coolant flow from the heater return to the water pump around the lower front of the engine...???...could that be rotted out and leaking...???

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    ckucia is offline Cadillac Owners Fanatic
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    Re: Cooling System Pressure Test

    That pipe seems OK, I actually removed the little piece of hose that joins the two halves (below the harmonic balancer) to be sure I had the coolant drained out of there, besides draining at the radiator.

    No drips and no hissing, and all the hoses are dry. The only thing wet is the intake manifold (only under the alternator and PS pump) and the area just below that down to the water pump. The face of the water pump is dry. Everything straight down from the head is wet, but nothing else next to the engine (and there is a lot crammed in there).

    The weird thing is I can't imagine there's all that much airflow, other than that caused by the alternator. Barring a crack in the intake manifold, I can't see how the coolant gets up there from a leak at the manifold-to-block or manifold-to-head gaskets or head gaskets, for that matter.

    The only thing that is "pointing up" that is wet is the water pump gasket.

    What would the oil look like if coolant was somehow getting into it? Mine's still nice and yellow from recently changing it and not being able to drive it all that much (and it doesn't smell like gasoline now that I've replaced the injectors). I don't think this is the case, but is there a telltale sign of coolant in the oil, or does it just puddle on top of it in the pan?

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    Re: Cooling System Pressure Test

    Quote Originally Posted by ckucia
    is there a telltale sign of coolant in the oil, or does it just puddle on top of it in the pan?

    Oil floats on water...so...if you get "water" in the oil it will form a layer on the bottom of the oil pan....all the oil will float on top of any water, right?? If there is water in the oil and the engine is running it will mix the two rapidly and form a milkly looking emulsion that is pretty easy to see. Run the engine for several minutes at 2500-3000 and then look at the oil on the dipstick. If it looks milky then there is coolant in it. Or...just remove the drain plug momentarily and look at what you get out. If there is water in there it will be at the bottom of the pan and come out first.

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    ckucia is offline Cadillac Owners Fanatic
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    Re: Cooling System Pressure Test

    No coolant on the dipstick. Added the supplement tabs and they appear to have addressed the leak. Been driving the car regularly since Friday without any apparent seapage. Still going to monitor it frequently.

    Thanks for all your help (again) bbob !

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    Re: Cooling System Pressure Test

    The cooling system sealer/supplement is excellent for sealing the nuisance type of leaks that you describe. Just keep it in the system to avoid future problems like that....

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    ckucia is offline Cadillac Owners Fanatic
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    Re: Cooling System Pressure Test

    Well, if I didn't believe in their use before, I certainly do now, although a part of me would have prefered to actually find and fix the leak, or at least identify it.

    OTOH, I'm driving the car regularly now. The Allante's my daily driver for most of the year, and it really is a great car when I can keep it on the road.

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    Re: Cooling System Pressure Test

    I know what you mean but as long as you know that it is not something that is going to fail catostropically one day don't worry about it. That is why the stuff is factory installed in many many different cars...it "fixes" tiny gasket surface imperfictions and porosity and minor cracks in castings without bothering a soul....

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