Cooling system doesn't de-pressurize

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Hey all -

My cooling system doesn't always want to de-pressurize when cold. I almost always have to use a towel to slowly open the rad cap so as to not take a coolant bath, and the upper hose is as hard cold as it is hot (not rock hard, but definitely under pressure).

Over the last few months, I've been tracing erratic coolant leaks that only seem to manifest when the truck is cold. Couple of months ago, it was the clamps for the heater hoses at the heater core end. A couple turns on the clamp screws and all was well. Then it started leaking again from the same area a couple of weeks ago after a long highway trip. This time, I took the hoses off, trimmed a bit off each end, and put on new clamps thinking maybe I pinched/cut one of the lines by tightening the old clamps too much. That worked just fine for about a week, but tonight I came home from work (driving my other vehicle) to find the heater hose that goes into the block was leaking at the block end. My guess is the extra pressure in the system is causing the weakest links to give up, so the leaking at the hose ends are a symptom.

Otherwise, the truck runs great. It idles at 203-205 (measured using an Autometer digital gauge with the probe installed at the port where the sensor for the 'ENGINE TEMP' light would be) and cruises anywhere from 199-210 depending one what you're doing, though mostly it stays right at the same temp as idle. There's no oil in the coolant (fresh Fleetcharge), it doesn't appear to lose/consume coolant, coolant doesn't smell like exhaust, nor does the exhaust smell like coolant. No white smoke either. Hoses are all new, t-stat is probably original, same with the water pump. Radiator is a Champion aluminum unit with a new OEM cap. Miles are right around 75K, original.

Please please PLEASE tell me it can be something way more simple (and less expensive) than head gaskets or cavitation. Maybe the little ball next to the t-stat is stuck?

Mike
 

riotwarrior

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Mike,

You seem to be running a tad warm IMHO as the Tstat opens at 192 IIRC, and that Champion rad cools just fine. I'd say you thermostat or something in there the ball is sticking.

FYI use only FORD Motorcraft, or IHI thermostats. Do not use any parts house branded thermostat.

I cannot see why you would be pressurizing without loosing coolant as a HG leak would cause pressure and usually loss of coolant.

Is the overflow tube blocked does the coolant tank hold coolant and does that level rise and fall with warm cold cycles?

Have you had that rad cap tested? Start with having it tested, if it checks out ok 16lbs, then I'd look further maybe into the Thermostat.

On another note...if you had an issue with HG or cavitation the system would depressurize over time when cooled as the pressure would go back into the HG or **** into the cyl from cavitation....just my thoughts, maybe I'm wrong....someone will chime in..

JM2CW

Al
 

Hydro-idi

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^^^What Al said. Those aftermarket thermostats are junk. Been there and done that. Very happy with my motorcraft t-stat. Like Al said, your temps should be running a little lower than that as well.
I am also thinking there is an issue with that radiator cap you are using.
 
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I have a OE thermostat laying around. Just been too lazy to install it.

As for the cap, are the units with the safety valve built in any good? Seems like it could at least save me a coolant bath the next time.

Overflow holds fluid fine. The hose is still the original, but is in good shape. Only thing I did was add a small clamp to the end on the rad side to keep it from sliding off because it seemed like a loose fit on the new rad.

Mike
 

The Warden

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I got that safety valve rad cap on my rig and it works well.
Makes two of us. IMHO the safety valve is a very good idea...I won't intentionally run a cap without one.

FWIW my truck's cooling system has always kept a bit of pressure in it, no matter how long the truck's been sitting. This is in spite of different pressure caps (both 14 and 7 psi), and in spite of having done the head gaskets. 75K miles or so and no cooling system-related problems, other than the occasional hose clamp needing to be tightened up. My old van was the same way. I just figured it's normal for these engines :dunno
 

icanfixall

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My feelings are either the clamps are not making a complete round clamping pressure on the hose or the hose is of low quality. As for the pressure not dropping to zero that probably is the cap. Nothing else can cause the pressure to stay in the cooling system. A stuck thermostst wont hold pressure because the water pump outlet side is connected to the radiater side of the stat. When the pump stops truning the pressure in the system neutralizes on both sides of the stat. A head gasket leak or cavatation wil allow the pressure to bleed off. Take the overflow hose off the radiater neck and blow thru it into the recovery tank. You should be able to pass lots of air. Sometimes these recovery hoses get some crap inside them from years of use. Then the system pressureizes fine. But when the system cools down it wont allow coolant to return to the radiater causing you to think you have a leak because the top tank looses coolant and there is no leaks found but the recovery level continues to gain coolant... This happened to me once.. Tuff thing to find too. Sometimes the hose gets soft and wont make a good seal on the radiater neck. Then it can't suck the coolant back into the radiater when it cools causing another low coolant issue. Seen that before too. Simple fix is replace the hose.
 

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Do you know a good diesel mechanic? I think I would have it checked out. Cooling system pressure is caused by coolant heating and expanding, once the coolant cools the pressure should be gone.:dunno

All of my 6.2-6.5 motors in the early stages of head gasket failure would hold pressure like that, because there is compressed air in the cooling system. When the leak is small, the relatively low cooling system pressure wont push coolant/air back through the leak.

An easy check would be to modify your cap to not hold pressure (so that coolant is vented to overflow at little to no pressure). If you have a combustion to coolant leak, you will have bubbles in the overflow after driving.
 

Black dawg

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Have you verified that coolant is able to pass from the radiator to the overflow? I have seen a blocked hose cause the same symptoms.
 
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So here's another weird part of the equation. The pressurization isn't consistent. I fixed the leak last night (took off the hose, cut off a bit, and put it back on with a new clamp), filled the system, burped it, then went for a 20-30 minute drive around town. I parked the truck in the driveway, which isn't its usual spot. Came out this morning and before I fired it up, I popped the hood and gave the upper hose a squeeze. No pressure. Also, no leaks. Thinking about it, I've never ever had it leak when it's in the driveway, which does have a bit of an incline to it. What's that all mean? I have no clue.

Waiting for it to cool off enough to install the 13lb cap with the safety valve built in that I just picked up today. I'll unhook the bypass hose and check it out while I'm at it.

Mike
 
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Just went and checked the bypass hose. Took the end out of the overflow, then blew back into the rad. Heard some noises in the area of the cap and was able to put a bit of pressure in the upper hose. Actually, that's another point. Coolant temp is about 165 right now and the upper hose has no pressure (well, had no pressure until I blew into the bypass).

I'll start calling around to find a shop savvy enough to check coolant for exhaust just for peace of mind. Meantime, I'm borrowing the old man's gasser to tow the bikes out to a well-deserved trackday at Willow Springs.

Mike
 

icanfixall

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What did you use to blow back into the radiater... I was just thinking your own air pressure. Lips around the CLEAN HOSE... Cause the antifreeze is poisen.. But being able to blow back thru it with lung pressure tells you the line is clear enough to suck coolant back into the radiater. If that line has any leaks in it there would be enough vacuum suction to pull fluids back into the radiater. Also keep the hose off the bottom of the recovery tank about an inch.. No reason to suck up the possible crap on the bottom.
 
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What did you use to blow back into the radiater... I was just thinking your own air pressure. Lips around the CLEAN HOSE... Cause the antifreeze is poisen..

But it's just so yummy!

Anywho, knock on wood, the new rad cap seems to be working. I installed a Motorrad unit from O'Reilly (13 lbs with the built in de-pressure lever) and have been checking the upper hose every time the system is cold. So far, it has always de-pressurized. Coolant level in the overflow is fluctuating predictably. Doesn't seem like I'm losing any. I'd still like to take it in to get the coolant checked for exhaust gasses just for peace of mind, but I'm having a helluva time tracking down a diesel mechanic in the San Diego area.

Kinda odd that the 'old' cap may be the problem since it was an OEM Motorcraft unit that had only been on there a couple of months, but I guess a bad one out of the box is to be expected every once in a while.

Mike
 

icanfixall

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Glad things are working out for you. Things like this can drive a guy nuts trying to find whats wrong. Seems like you found it so drive on but continue to watch till you feel nothing is suspect...
 
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