Posted: Feb 28 2008 at 12:27am | IP Logged

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supbud:

... The two most common causes are thermisat (sticking or upside-down) and/or a collapsing intake hose. A 50-50 antifreeze mix gives a higher boiling point for better protection.

Posted: Feb 29 2008 at 6:00am | IP Logged

What year truck?  What's the mileage?  Which engine? 

Has the rad or heater core been replaced (which would make me more suspicious about air in the system when it was refilled)? 

To start with, for the cost of that gasket, I'd be popping out the thermostat housing just to confirm it's in correctly.  I'm kinda thinking it's gonna be an upside-down thermostat because it almost sounds like some kind of obstruction in the flow of the coolant, but that's just a guess. 

The most bizarre story of overheating I have ever heard is actually my own story... My first car, a 1976 Ford Capri (No, not Mercury, Ford).  I had an overheating problem with it.  We flushed the system, individually flushed the heater core, actually replaced the rad, and still no change.  And then a family friend was looking at the fan blade that we'd pulled off the water pump for the umpteenth time and says "You know, this isn't a Ford part".  On closer inspection, the blades on this thing were reversed in their deflection from center, so instead of pulling air through the radiator and across the engine, it was blowing it forward into the radiator, so that whenever the car was in motion, the airflow was being obstructed through the rad by the force of the wind being blown forward... ???... No joke, couldn't believe it.  Went to the wrecker, got another blade, and it solved the problem.  We never did figure out what the fan blade was from, but there wasn't an automotive stamp on it.

If you've had a lot of problems with the place that did the work, go somewhere else.  I'd almost want another pressure test done somewhere else just to be sure.  

Posted: Feb 29 2008 at 4:25pm | IP Logged

Supbud,

Just a quick rundown on how the cooling system works.  The heat created from the combustion process is transferred through the cylinder walls and heads and into the water jackets that surround them.  When that coolant is hot enough (185-210 degrees depending on the thermostat) the thermostat opens and allows that hot coolant to get pumped into the radiator to be cooled down and is replaced by the coolant that was previously in the radiator getting cooled down by the airflow through it.  The water pump simply keeps the coolant flowing all the time. The thermostat is a temperature sensative valve that only opens when the coolant (on the engine side) is at this predetermined temperature and closes again after the much cooler coolant from the radiator rushes in.  The fan clutch is much like a thermostat in that it is also temperature sensative, only, when the temperature of the air passing through the radiator is hot enough, then the fan clutch causes the fan to "lock up" rather than slip like a "clutch".  In the "locked up" mode, it pulls more air through the radiator and will unlock when the temperature comes down.  Any air that gets stuck in the system will create "hot spots".  If the air that is trapped is under the thermostat, then the thermostat cannot sense the temperature (it can only sense the temperature through a liquid).  It is somewhat common practice to drill a small hole (1/32 - 1/16") in the flange of the thermostat to prevent any trapped air. If the hole is drilled any larger than that, it can cause the engine to run too cool because too much coolant is bypassing it.  The heater core is simply a small radiator that is housed inside the cab of the truck. There is a valve to control how much coolant is flowing through the core and a fan to blow that hot air through the vents. A leak coming from any part in the system will allow air to enter into the system, which is the purpose of pressure testing the system.  When filling the cooling system, fill the radiator up, then start up the truck and let it run with the radiator cap "off".  Watch the flow of the coolant as the truck heats up, when the engine hits the proper temperature (as determined by the thermostat) the thermostat will open and you'll see the level in the radiator drop suddenly.  As the level drops, add coolant into the radiator quickly until it is within 1-2" of the radiator neck.  Continue to let it run and watch the level and the temperature gauge.  The temp gauge should be steady between 185-200 and the level in the radiator should be steady. After about 5-10 mins. put the radiator cap on then watch the temp gauge, it should remain steady. Then take it for a test drive and continue to watch the temp gauge.  Also, a 50/50 - 60/40 mix of coolant raises the boiling point of the coolant.  If you apply pressure to the system in the form of the radiator cap, that also raises the boiling point of the coolant, which is why it's important to change out your radiator cap every few years.  NEVER USE CHEAP PARTS!!!!!!  You get what you pay for.  If you find one thermostat for $5 and one for $20, always buy the more expensive one.  You don't want to blow a head gasket because you saved $15.

While I didn't go over everything, I hope this gives you some idea of what your system does.  Make it a habbit to replace your coolant, thermostat and radiator cap at the same time, then replace the hoses AND clamps every other time you change your coolant.  This will prevent alot of headaches and give you "Peice of mind"

Take care!!

Posted: Feb 29 2008 at 5:09pm | IP Logged

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Nelson37;

Thanks for a very nice post. You might want to make a slight change to your article.

"There is a valve to control how much coolant is flowing through the core and a fan to blow that hot air through the vents."

Correct me if I'm wrong.

The flow of coolant through the heater core in most modern vehicles is also used as a recirculation system when the thermostat is in the closed position. Do not impede this flow. It also helps cool certain areas of the engine when the thermostat is open. There is a door in the heater duct to control the amount of heat entering the cab.

The old cars had a cable controlled valve to regulate coolant flow to the heater core. 

Have a good one while you can still laugh about it.. Don S..

It would be nice if our members would add their vehicle information to their signature (similar to mine) plus add their City and State . A member in the same town might be willing to drop by and help you with a problem. Or drink all your beer!

Posted: Mar 01 2008 at 1:38pm | IP Logged

Lakota,

Like I told subpud, I didn't go over everything. I just wanted him to have the basics. Imagine if I would have gone into the reverse cooling systems on the corvette!  I figured I gave him enough info. and didn't want to make it too complicated.  Though yes, the old cars had cable actuated control valves to control the amount of coolant, some of the newer cars use vacuum operated control valves and now you usually don't see them at all.  It depends on the engineers and whether they just want to use the old technology or if they are actually willing to earn their income!  Though I'm a big fan of "It it ain't broke, don't fix it!!!!!"  I think manufacturers should constantly strive to "perfect" their product rather than change it every few years and have to keep working out the bugs.  Perfect the mechanical, but change the body!

If I'm ever in Ft. Worth, I'll make sure to stop by and drink all your beer!!!