Temp At 240 Please Help....

My 98 chevy K 1500 5.0 is running at 240 degrees. Last week I replaced head and intake gaskets. along with three different thermistats. first two would not open. There is no air packets in cooling system.also has new heater core which is a month old flushed radiator and block to make sure there was no blockage. With in five minutes of runnig truck will reach 240. If you take the stat out the truck runs at about 125. the only thing that has not bin replaced is the radiator and water pump.

Feel your upper and lower radiator hoses after your truck warms up. Are they different temperatures? If so, I would suspect maybe the stat is sticking again, or the waterpump isn't curculating.

BTW, what brand stat did you go with and what temp? Isn't the stock them on these truck 195? I would stick with a delco stat or esle super stant brand. None of them junky cheapo ones.....

both hoses feel the same temp and the stat is 198 degree from carquest and its the third stat today..

Oddd, Stupid question, but are you putting it in in the right direction? Spring side goes toward the engine.

that is a stupid question. AND NO IT NOT!!!!!!!!!!!!!!!

that is a stupid question. AND NO IT NOT!!!!!!!!!!!!!!!

not really a stupid question....with your problem this guy is very correct...there are a lot of stupid people on these forums...thats why there here to learn and save some money/time with vehicle issues...

since you have no overheating with the thermostat removed I would say you have the wrong thermostat or defective ...many a thermostat made today is chinese crap...get the correct exact replacement for your engine ...and as he also stated 198degF is an incorrect thermostat..for your engine..that is an odd temp..

the thermostat should have a small hole in it so that the coolant can very slightlly bypass it...this then allows the thermostat to open as the coolant flows...obviously if you have the wrong thermost this will not occur...

so your saying because my lower and upper radiator hoses are not warm as well as they radiator. that this is caused by the wrong thermistat.

so your saying because my lower and upper radiator hoses are not warm as well as they radiator. that this is caused by the wrong thermistat.


think about this !!!! the thermostat don't open so how are the hoses going to get hot ?????????????????????

the damm engine becomes a pressure cooker! hoses never get to see any heat, NO FLOW .......

so your saying because my lower and upper radiator hoses are not warm as well as they radiator. that this is caused by the wrong thermistat.

just thought of this ,,, this is the same type of problem one would find when you don't have enough antifreeze on a very cold day...the coolant in the radiator freezes and the engine overheats..

the hoses are frozen and the engine is smoking hot..same as your engine ,,NO flow!

what is your problem sorry if this questions are stupid to you but a have had along day and my head is not on straight because my mother jus died today smartass

Last week I replaced head and intake gaskets

Is the fan shroud on?

what is your problem sorry if this questions are stupid to you but a have had along day and my head is not on straight because my mother jus died today smartass

well sorry to hear that about your mother ....I wouldn't be even thinking of a vehicle problem if TODAY my mother died...

its only a hunk of iron and plastic..

Is the fan shroud on?

did you put coolant in it ..

I live two hours away and this is my only vehicle and i have to have it fixed yesterday i guess i trie the stat for a 4th time and yes the fan shroud is on

I live two hours away and this is my only vehicle and i have to have it fixed yesterday i guess i trie the stat for a 4th time and yes the fan shroud is on

seriously now drill a 1/8inch hole threw the thermostat..this will allow coolant to flow and then the thremostat should open correctly...

thanks for the help will try drillin a hole...

thanks for the help will try drillin a hole...


how did this all work out ?

Turns out it was a bad head Gasket goin to tear into it later this week thanks for the help guys...............

Turns out it was a bad head Gasket goin to tear into it later this week thanks for the help guys...............


new head gaskets don't fail..this is usually bad heads warped....

or improper torque, over stretched head bolts..

make sure you have good new hardware, heads check for no distortions,use the proper assembly proceedure to ensure the correct head bolt stretch to prevent gasket / leak issues..

use the correct material on the head bolt threads....clean out the head bolt thread holes in the block..etc.....

Good to see you found something, but I would double-check your coolant temp sensor to be sure it is really hitting 240°. A $30 infrared thermometer aimed at the t-stat housing will give you a decent indication of overheating as well as when the t-stat is opening up. If that checks out okay then your next item to replace would be the water pump.

We're all just trying to help. We've all done dumb things because it was late or tired or under duress...we're human. The only stupid question is one not asked.

Hope this helps!

that is a stupid question. AND NO IT NOT!!!!!!!!!!!!!!!

Thanks j_cAT for the backup and remarks.

Man, sheesh, sorry to hear about your mom, but chill out. I was just trying to help. If the stat is in backwards, it will cause issues just as you describe. I have ordered numerous stats from o'reilley's and advance and most come with the o-ring on the wrong direction, so thats why I asked. It would be easy for someone to install it backwards. You dont need to get all bent out of shape about it. I was not trying to insult your intelligence, but maybe we should question it as this is the second go around for head gaskets it sounds like.

This time around make sure to use fel-pro severe duty gaskets, writing facing up, new head bolts (you will need two sets, one set for each head) and dont forget to use plenty of silicone for the valley gaskets and in the corners or they will leak.

after he opens up this engine I would be surprised if it is only a head gasket...with or without a thermostat if the heads/gasket is bad and exhaust gases get into the coolant system all that air in the coolant will prevent coolant flow , as the water pump can't pump air...

I have seen engines with blown heads still overheat the engine with no thermostat....just removing the coolant cap and running the engine this is easy to see...

Ros981500,

First off, you draw more flies with sugar than vinegar, so you may want to be a little nicer to those that are trying to help you. We on AF have always worked on the K.I.S.S. principle (Keep It Simple Silly). Especially with the emotional loss of your mother stacked on top of your problem, it's very possible that you could have put the t-stat in backwards, so relax. Flaming and abusive comments are against AF policy, so me and the rest of the AF moderating staff would appreciate it if you would refrain from doing so.

Now to your issue. Put the supposed stuck t-stat in a pan of water (suspend it so it doesn't touch the bottom or side of pan). watch the t-stat, and it should start to open as the water starts to bubble, and should be fully open by the time the water reaches full boil. If it doesn't open it is indeed bad, maybe get a real t-stat like a delco rather than a store brand. I doubt you got 3 in a row bad, but it's not impossible.

If the stat opens, have you checked to be sure water is flowing through the radiator? If you don't have good flow, either the radiator is blocked or the water pump isn't circulating. This doesn't explain why it runs too cool (125) with the stat out, but it's something else to check. It's also possible you have an air pocket. With the restriction of the t-stat out, the air pocket will force it's way out and it will circulate, but with the t-stat in, the restriced flow isn't strong enough to force the air pocket out, so it overheats very quickly due to the sensor not being immursed in liquid, it's sitting in an air pocket. This may be what took out the head gasket again as you mentioned in post 19.

i almost lost a brand new motor to a defective water pump.it was a rebuilt and the impeller fan wasn't pressed onto the shaft so it would only flow a small amount.it was the last rebuilt water pump i ever bought and that was 19 years ago.so check to make sure that the water pump is flowing as well.

Replaced head gaskets again with heavy duty. when i tour into it the passenger side gasket was blown out between 6 and 8. replaced both and put on new pump runs great. sorry about the remarks made guys it was just a horrible day................

Replaced head gaskets again with heavy duty. when i tour into it the passenger side gasket was blown out between 6 and 8. replaced both and put on new pump runs great. sorry about the remarks made guys it was just a horrible day................

thanks for the reply on your repair..
any idea on why ?