too much pressure in cooling system

anggi821October 31, 2007

I have a 95 sable that lost heat about a year ago. We put in a new thermostat and that didn't fix it, so we took it in and it was full of sludge so we had it flushed out. The tech said the radiator and heater core looked fine and seemed to be operating fine. My heat came back and it was fine the rest of the winter. then summer came and you could smell that it was very hot so once agin we flushed out the sludge and it seemed to be fine. Now I lost heat again and the sludge has began to boil out the reservoir. So today my husband flushed it out again and the water coming out is crystal clear and we replaced the radiator cap. I have heat again but the pressure is still building to fast and to much. After running for 5 min it was so full of pressure that when he popped the rad cap, it bubbled out the neck. By the way, my husband has been a mechanic on and off for the last 15 years, so he does know about taking off a rad cap when it's hot. But, he's at a loss as he has never seen it boil in the reservoir. We went to a rad place, and all they want to do is replace the rad and core, but still can't explain what's causing the pressure to build up and boil in the reservoir. We also thought about a cracked head, but that doesn't add up either. If anyone has any thoughts, please share!!! The mystery is becoming a nusance. My husband has talked to other mechanics he has worked with and we've already done what they have thought to try. We're pretty sure that the sludge is not oil, but rust particles coming from the rad. Oh...It also runs in normal range for the temp gage and has not overheated.



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Not enough info. what motor size ? What is your definition
of " sludge " ? That car will have a 3 lt. or 3.8 lt.
The 3.8's are BAD for head gaskets. What is your definition
of " two much pressure "? Normal pressure in 5 minuets will
make the upper rad hose so hard you can't squeeze it. You
might want to replace the rad and heater core and have the block flushed. If there is that much sludge in the rad
your transmission will over heat. Not good. No offence but if your husband is a mechanic he should know about the 3.8
and when you pop the rad cap off any heated engine the
boil over is normal. Again no offence but he may have been
a mechanic more off than on. The rust you see is from the
block. You have an aluminium rad. If there is enough rust in the system it will insulate the temp. sensors and never show an over heat condition. Prime example. Remove all antifreeze and run the engine until it seizes from over heating. Your temp gauge will not come off cold. No antifreeze to transfer heat to the sensor. Argo no temp reading. If the antifreeze has never been changed or flushed every 3 years and the motor HAS over heated you have a problem. Good luck. Maybe someone else will help you with a very simple repair. I've given you the worse possible reply. ( can't spell senario ). Again, good luck.

    Bookmark   October 31, 2007 at 7:09PM
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Thanks for your reply...

The motor is a 3lt. with 91,000 miles. I have only had the car for 2 years, so I don't know what prev. owners have done though I have done the "usual maintness". The sludge looks like fudge, but when smoothed out or rubbed between fingers, looks more rusty red brown in color. No smell and no seperation (like oil and water). And you mentioned no temp reading, I do remember when I lost heat the first time, the temp needle never moved off cold and the rad place I took it to couldn't figure out why as they said everything was working properly. Though since the first flush, the temp gage has been working. Out of the last 15 yrs, my husband has been a mechanic for about 8 of those years and is pretty knowledgeable with cars, but (as most people we have talked with) has never seen sludge boil and overflow out of the reservoir. The few people we spoke to, one of which has over 35 yrs of continual exp said it sounded like to much pressure, to change the rad cap. So we did and still no change. Again, thanks for the reply and hopefully the additional info will help to further figure out my issue.

    Bookmark   October 31, 2007 at 9:29PM
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That's too much sludge buildup between cleaings. There has to be a cause. Possibilities:

1. Head gasket leak - blowing combustion products into the coolant.

2. Air is emtering the "closed" coolant system. A major cause of corrosion in the coolant system is admission of air. Check out the tubing/hose that connects the overflow bottle to the system. Look at the underside and at bends. Air can be drawn into the system upon cooling. As the pressure falls in the engine and goes negative (relative to the atmosphere), coolant normally flows back into the engine/radiator, but if there is an air leak in the connecting tubing, air will be drawn in instead, and the engine will develop hot spots the next time it is run.

An improper or ill fitting cap can cause problems.

    Bookmark   November 1, 2007 at 12:49AM
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Get a cooling system pressure tester. That will tell you if you have any leaks. Test or replace the radiator cap. With it full of coolant, start and observe coolant with the radiator cap off. A steady stream of bubbles that doesn't stop indicates a head gasket leak. Get a thermometer, gage you can temporarily install in a water jacket, or one of those point and shoot type heat detectors. The object of those suggestions is to determine if you have any leaks and if the engine is hot cold or normal temperature. Your story contains a variety of symptoms, some of which sound like a normal conditions to me that you've concluded is part of the problem. Need to separate what the normal conditions are from the abnormal.

Flush and refill using green or yellow antifreeze. Stay away from the orange dex-cool stuff. It has a reputation for causing the kind of problems you describe. Make sure all the air is out of the cooling system. Air gets trapped in some engines and is difficult to remove. I've found it helpful to drill a small hole in the flange of the thermostat to let the air out so the system can be filled.

Personal observation from years gone by, often times cooling systems in Ford products got full of rust a lot quicker than most for some reason. Some I used to flush about every year to keep reasonably clean for some reason. There may have been a cause, but neither I nor anyone else in the shop I worked in at the time knew what it was. jmo

    Bookmark   November 1, 2007 at 8:15AM
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You are describing a leaking head gasket. Also as Gary
said that engine, and i have 3, are very prone to air locks
as the coolant is refilled. It could take 1/2 hour to bleed
off the air and it isn't fun. you DO NOT put the rad cap on and hope for the best. It will boil over. are you sure you are not getting transmission oil in the rad ? I have seen head gaskets go in that type of engine. Pretty rare.
antifreeze that comes out brown is usually burnt and VERY
high in acid. when you plug in your block heater it will
short out as the antifreeze burns through it and burn the
antifreeze again. A domino effect. Have them do an acid test on your antifreeze and a " hot engine " pressure test. Good luck.

    Bookmark   November 1, 2007 at 12:57PM
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Thank you for all the responses!!!

    Bookmark   November 1, 2007 at 6:56PM
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I know this was from 2007. I had put prestone radiator sealant in radiator. Messed up thermostat. Blew hose . And water kept bubbling out but with a spoiled milk look to it. Replaced thermostat and flushed it. Water kept boiling. Well after 5 hours of that. It came down to science. Water boils around 200o and my fan wasnt turning on till 222o so we raised boiling point. If you add 50/50 antifreeze , you will need two jugs. Or the super strength and add the rest water. It worked. Note: we had a chrystler pacifica 160,000 miles base. 2006. We also had the computer to watch temp because chry....doesnt have temp gauge.

    Bookmark   March 8, 2015 at 6:52AM
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The boiling point is raised by increasing the pressure of the liquid. I do not have pressure tables for ethelyene glycol-water mix, so I will use that for water to illustrate the change in boiling point with pressure. The following table was extracted from the Handbook of Chemistry.

Deg F Pressure, psia (absolute pressure)

212 14.696
213.8 15.228
215.6 15.776
221.0 17.521
249.8 29.717

Water boils at 212 F at one standard atmosphere of pressure. or about 14.7 psi. If a pressure cap of a radiator adds 15 psi (or 29.7 psia), then the boiling point is raised to about 250 F. In other words, a radiator with a 15 psi cap will not boil until the water temperature raises to 250F. At 250 F, that system is dangerous. If the cap is suddently removed, most of the liquid will flash to steam and gush out of the opening scalding anything it touches.

A closed, non-leaking automotive coolant system filled with water with a 15 psi cap will not boil until it gets to 250 F. A leaky system can boil as low as 212 F. However, the coolant does expand while it is heating.

Here's what supposed to happen. As the coolant expands, it squirts by the pressure regulator in the radiator cap and goes to the overflow bottle. The cap should have an second seal under the very top of the cap. This gasket is supposed to seal the overflow tube from the atmosphere. When the engine cools down, liquid from the bottom of the overflow bottle is sucked back into the radiator, that is, if the radiator cap's outer seal is working. If the overflow bottle is not completely emptied, then no air gets back into the coolant system. This is critical. It is the admission of oxygen into the coolant system that causes most of the corrosion and crud. After a few heating and cooling cycles, most of the air in the coolant system should be flushed out and no more will get in until the system is opened again, for example, opening the radiator cap or allowing the overflow bottle to go dry.

This system fails when there is a leak somewhere from the radiator cap to the overflow bottle. One typical cause is a wrong radiator cap. A cap from an older system without an oveflow bottle may fit but it does not have the second seal under the cap. It has only the pressure regulator. A second cause is a proper cap with a second seal that no longer works. Another cause that I have seen is a leak in the hose that goes from the radiator to the overflow bottle. I had a hose that had a slit in its underside that could not be seen from above.

From what you have written, your fan may not be turning on soon enough. For example, the original equipment temperature sensor for '97 Saturns was notorious for failing after about 3 years and not turning on the fan. After replacing one twice in our Saturn, I found an after market sensor with a metal sensor nose that lasted for years. The original equipment sensor had a plastic nose that eventually dissolved in the hot coolant. The head cracked on this engine at 130,000 miles probably due to over-aging of its aluminum alloy head.

    Bookmark   March 9, 2015 at 12:44AM
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