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Radiator fluid rises when cap off?

Old 05-27-2019, 12:42 PM
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Radiator fluid rises when cap off?

Have a 83 4x4 new jasper motor 3 years ago and new radiator. Had problems with temp going back forth. With radiator cap off and cold start, fluid starts to over flow. Major problem or easy fix?
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Old 06-04-2019, 05:01 AM
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Sounds like a faulty thermostat. On cold starts the thermostat should be closed, to allow the coolant in the engine to warm up faster, allowing the engine to warm up faster. It is then supposed to open at a certain temp, usually about 180-195 degrees F, to allow the coolant to reach the radiator & "cool the coolant".. There shouldn't be any coolant flowing from engine to radiator when cold, so this sounds like the thermostat is stuck open, or otherwise malfunctioning.

As long as there is nothing majorly wrong with the engine internally, it's not a huge job to replace the thermostat. Just take your time & make sure you have the correct temperature rated replacement thermostat & use a new gasket on the thermostat housing to prevent leaks. It would also be wise to completely drain & replace the coolant if you haven't done so in the 3 years since the new motor.

More info about this repair:
https://toyotachinook.files.wordpres...ckup-alive.pdf
Page 143
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Old 06-04-2019, 07:55 AM
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Seems normal to me. When water gets hotter it expands. The radiator cap holds that back to some extent, but once the pressure exceeds the cap's rating, it overflows into the overflow tank. Once the engine is shut off and cools, the coolant contracts and the pressure drops. The cap is also designed to allow coolant to suck back from the overflow tank. Make sure the hose that goes into the inside of the overflow tank isn't broken or missing as this will not allow the coolant system to re-fill when it cools. It will suck air back in.

So when you take the cap off and start the truck, the coolant starts to warm up and expand. Since the cap is off it just starts to slowly overflow rather than get pushed into the overflow tank.

Of course, you could have a problem like a blown head gasket but you'd probably have a lot of bubbles in the coolant rather than a slow steady overlflow.
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Old 06-04-2019, 11:58 AM
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Originally Posted by 13Swords View Post
Sounds like a faulty thermostat. On cold starts the thermostat should be closed, to allow the coolant in the engine to warm up faster, allowing the engine to warm up faster. It is then supposed to open at a certain temp, usually about 180-195 degrees F, to allow the coolant to reach the radiator & "cool the coolant".. There shouldn't be any coolant flowing from engine to radiator when cold, so this sounds like the thermostat is stuck open, or otherwise malfunctioning.

As long as there is nothing majorly wrong with the engine internally, it's not a huge job to replace the thermostat. Just take your time & make sure you have the correct temperature rated replacement thermostat & use a new gasket on the thermostat housing to prevent leaks. It would also be wise to completely drain & replace the coolant if you haven't done so in the 3 years since the new motor.

More info about this repair:
https://toyotachinook.files.wordpres...ckup-alive.pdf
Page 143

Thank you.
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Old 06-06-2019, 05:50 PM
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Originally Posted by 13Swords View Post
Sounds like a faulty thermostat. On cold starts the thermostat should be closed, to allow the coolant in the engine to warm up faster, allowing the engine to warm up faster. It is then supposed to open at a certain temp, usually about 180-195 degrees F, to allow the coolant to reach the radiator & "cool the coolant".. There shouldn't be any coolant flowing from engine to radiator when cold, so this sounds like the thermostat is stuck open, or otherwise malfunctioning.

As long as there is nothing majorly wrong with the engine internally, it's not a huge job to replace the thermostat. Just take your time & make sure you have the correct temperature rated replacement thermostat & use a new gasket on the thermostat housing to prevent leaks. It would also be wise to completely drain & replace the coolant if you haven't done so in the 3 years since the new motor.

More info about this repair:
https://toyotachinook.files.wordpres...ckup-alive.pdf
Page 143
Changed out thermostat and no longer over flows!
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Old 06-07-2019, 04:06 AM
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Temps

Well temp gauge still goes up a tad during freeway drive. Gauge goes down during city driving.
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Old 06-07-2019, 06:38 AM
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Originally Posted by joesgarage View Post
Well temp gauge still goes up a tad during freeway drive. Gauge goes down during city driving.
Glad you solved the overflow problem. Sounds like the thermostat was stuck open after all. The temp gauge going up a bit on a freeway drive is perfectly normal. It's a bit lower on city driving as the cooling system has time to get rid of excess heat while idling at stoplights. As a rule of thumb, as long as it's consistently below half on the temp gauge I wouldn't worry. My 20R runs at 1/4 all the time.
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Old 06-07-2019, 07:15 AM
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Originally Posted by 13Swords View Post
Glad you solved the overflow problem. Sounds like the thermostat was stuck open after all. The temp gauge going up a bit on a freeway drive is perfectly normal. It's a bit lower on city driving as the cooling system has time to get rid of excess heat while idling at stoplights. As a rule of thumb, as long as it's consistently below half on the temp gauge I wouldn't worry. My 20R runs at 1/4 all the time.
It goes 3/4 of the ways.
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Old 06-08-2019, 05:57 AM
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Originally Posted by joesgarage View Post
It goes 3/4 of the ways.
That's still OK but you might want to consider doing one more thing. Replace the temperature sending unit/sensor. It is over 35 years old and may not be accurate, especially if it's been "cooked" a time or two before. Another easy fix, It's usually located just below the thermostat housing & has one wire going to it.

https://www.rockauto.com/en/catalog/...+/+sensor,4748

How is your radiator cooling fan clutch? It should be the fluid coupling type. Tests & info here:
https://itstillruns.com/test-fan-clutch-5086903.html
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Old 06-09-2019, 11:44 AM
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Today. Normal range?


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Old 06-10-2019, 04:44 AM
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That's a bit high but as long as it doesn't go beyond that you are probably ok. I'd still replace the temp sender tho, & check out the fan to make sure it's working ok.

Other thought. You could also have some air in the cooling system, causing it to run more hot than usual.
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Old 06-18-2019, 11:47 AM
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Originally Posted by 13Swords View Post
That's a bit high but as long as it doesn't go beyond that you are probably ok. I'd still replace the temp sender tho, & check out the fan to make sure it's working ok.

Other thought. You could also have some air in the cooling system, causing it to run more hot than usual.
As someone who just blew a head gasket, heed this advice and take the time to get all that air out.
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Old 06-18-2019, 07:45 PM
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Originally Posted by swampedout View Post
As someone who just blew a head gasket, heed this advice and take the time to get all that air out.
How do I do that? I’ve tried the “put truck on incline, cap off and run heater”. Is there a time I should run the truck like that?
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Old 06-18-2019, 11:17 PM
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Originally Posted by joesgarage View Post
How do I do that? I’ve tried the “put truck on incline, cap off and run heater”. Is there a time I should run the truck like that?
That's usually a good way to do it. I also squeeze the hoses repeatedly until no more bubbles come up to the rad cap opening. If you are willing to spend a little money a spill free / spill proof funnel is a pretty awesome tool to have in your arsenal and makes the whole burping with the cap off technique really easy and clean.

One other thought is that you may want to test your temp gauge. Pulling the instrument panel out isn't too difficult and the test for the temp gauge is really simple if you have a multimeter.

Last edited by FourEyes; 06-18-2019 at 11:22 PM.
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Old 06-19-2019, 12:53 PM
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Originally Posted by FourEyes View Post
That's usually a good way to do it. I also squeeze the hoses repeatedly until no more bubbles come up to the rad cap opening. If you are willing to spend a little money a spill free / spill proof funnel is a pretty awesome tool to have in your arsenal and makes the whole burping with the cap off technique really easy and clean.

One other thought is that you may want to test your temp gauge. Pulling the instrument panel out isn't too difficult and the test for the temp gauge is really simple if you have a multimeter.
Going to try to burp again with funnel, thanks.
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