Keith Browning Posted February 27, 2010 Share Posted February 27, 2010 I never gave this much thought but concerning the thermostat issue on these engines we were given an SSM and a TSB in which Ford uses the word "hyperextended". Exactly what the hell is that supposed to mean? It seems to me that the t-stats are either sticking or have experienced some kind of damage anytime I have had to mess with them and a few of our members have reported damage or debris. So, hyperextended? Are they opening too far? Blocking passages? Has anyone heard a better explanation? The DTS gets e-mails on this and I don't know what to answer with. Quote Link to comment Share on other sites More sharing options...
GregKneupper Posted February 27, 2010 Share Posted February 27, 2010 When they are hyperextended you can physically see that when you remove the thermostats that they are starting to come apart making it longer than it should be. It is usually on the high flow thermostat that has the problem. When it hyperextends the round disc that is on the bottom of the thermostat will actually press against the front cover and block the passage for coolant to flow. I replace about 4 of these a week in the 6.4. I may have one under my bench that I can take a picture of. Quote Link to comment Share on other sites More sharing options...
Keith Browning Posted February 27, 2010 Author Share Posted February 27, 2010 Excellent explanation Greg! Thank you. I "kinda thought" something to that effect... Quote Link to comment Share on other sites More sharing options...
joshbuys Posted February 27, 2010 Share Posted February 27, 2010 Yep - I've seen several of these hyper extended t-stats - like Greg said - mainly on the high flow (longer of the 2) thermostats. Quote Link to comment Share on other sites More sharing options...
Aaron Posted February 28, 2010 Share Posted February 28, 2010 What was the symptoms, Josh and Greg? Or were these discovered during radiator/stat replacement as per TSB (updated last week dont remember the number so they could eliminate .4 for the road test ) Quote Link to comment Share on other sites More sharing options...
joshbuys Posted February 28, 2010 Share Posted February 28, 2010 I've seen several with repeat radiator leaks (after 't' installation) over heating/coolant temps change very rapidly when driving down the road (monitor ect/eot). Seen one that had a repeat horizontal egr cooler failure. On a side not - did a set this last week on a truck that had 98K miles on it - wouldn't blow warm air - after idling for an hour the ect was around 90*F - the rubber seal on the thermostats was peeling off and on the longer one it was pulled back about 1/3 of the way around. First time I've seen one like that on these. Quote Link to comment Share on other sites More sharing options...
Aaron Posted February 28, 2010 Share Posted February 28, 2010 Funny you should mention that, when I was moving back from the NWT, I stopped in to see Mr. Warman and he had some stats out of a truck that had failed, just like that. Quote Link to comment Share on other sites More sharing options...
cbriggs Posted March 1, 2010 Share Posted March 1, 2010 Ya, Ive seen a few with the rubber seperating. Quote Link to comment Share on other sites More sharing options...
GregKneupper Posted March 2, 2010 Share Posted March 2, 2010 Josh said it right. That is exactly the problem. Overheating and at times stuck open causing a p0128 in the pcm. Another sypmtom of it is excessive cooling fan cycling. Quote Link to comment Share on other sites More sharing options...
GregKneupper Posted March 11, 2010 Share Posted March 11, 2010 Here is a picture of a hyperextended thermostat that I replaced this morning. As you can see the round disc on the bottom of the larger thermostat is sticking out further than usual. This is not even the worse on that I have seen. I have seen some that are so far extended that they actually hammered an indention in the front cover where they were slamming on it. [img:center][/img] Quote Link to comment Share on other sites More sharing options...
Keith Browning Posted March 28, 2010 Author Share Posted March 28, 2010 Alright, I am still trying to put an article together and the more I look at the system, the more questions I have about the thermostat issue. The only place I can find mention of the bypass is in the Coffee Table book, page 17: ___________________________________________________________________ A dual thermostat system is used to control the flow of return coolant to the radiator. If the thermostats are open, coolant flows to the radiator to be cooled. The bottom thermostat has a bypass circuit that will allow coolant to return to the pump when the thermostats are closed (speeding engine warm up). ___________________________________________________________________ Correct me if this is wrong: the bypass is OPEN when the engine is cold allowing coolant to recirculate back to the pump causing the coolant to heat up faster. We can conclude that when the coolant warms up the bypass valve closes preventing coolant recirculation and allowing full coolant flow to the radiator when the thermostats open. If the valve is Hyperextended effectively meaning that the valve is stuck closed, shouldn't we conclude that the symptoms would simply be longer warm up times rather than over heating and radiator failures? The more I think about this the more I am convinced that the bypass has less to do with this condition than the actual "thermostats." Maybe I need to hear an explanation directly from someone at Ford. Unfortunately all you see in print is the word hyperextended being tossed around. I suspect that the same failure that causes the bypass to stay extended also affects the main valve but you don't see the effects because the main valve is stopped by the seat. Essentially the condition that causes the hyper extension is preventing the valves to open at the proper temperature... I think I am losing it! Quote Link to comment Share on other sites More sharing options...
rlchv70 Posted March 29, 2010 Share Posted March 29, 2010 You are correct. If the t-stat is "hyperextended", then the "main" t-stat does not function properly. Quote Link to comment Share on other sites More sharing options...
fordtech03 Posted April 9, 2010 Share Posted April 9, 2010 So does this tie into the front cover cavitation problem? I was replacing some t-stats recently and noticed they had begun to erode the sharp edges inside the housing plus some slight metal particles in it. I pulled the water pump and sure enough the cover was all pitted/eroded inside. Quote Link to comment Share on other sites More sharing options...
GregKneupper Posted April 9, 2010 Share Posted April 9, 2010 I was told originally that the t stats would fix the front cover issues. I dont believe that the t stats were actually causing the cavitation but since the radiators were blowing out due to faulty t stats and people kept driving the trucks the low coolant level was causing the cavitation. Now if you are working on a 450 or 550 this is a different story. I have seen those chew through covers with no coolant leaks at all. I was told this is due to the high engine load that these engines are subjected to. The water pump is so large on these engines that they actually produce a vacuum on the inlet side causing bubbles to form and eventually cavitating the cover. Our fse said that they were destroying covers in 6000 miles during testing on these. Quote Link to comment Share on other sites More sharing options...
rlchv70 Posted April 9, 2010 Share Posted April 9, 2010 Running with broken t-stats may exacerbate the pitting on the front cover. With aluminum, some amount of pitting is considered normal. Quote Link to comment Share on other sites More sharing options...
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