[Willow]

Been having this issue since last summer. I replaced thermostat 3 times (thinking a faulty one), fan does come on, checked for leaks with dye and UV light (only place I saw dye is out of overflow), did a chemical flush today...still no change. Only an issue when it gets over 75...then temp rises...I turn on heat to bring it down to normal and have to run with heat on. Not fun when it is heat index of over 100 out! Suggestions on what to try next?

Sorry...didn't state what vehicle...2002 Chevy Silverado 1500 5.3 liter 4x4

 

[tbplus10]

Just a few items to check, since it overheats at high speed/high rpm the fan shouldnt be affecting things.
Do you have a larger than stock bumper or a winch blocking airflow in the front?
Is the radiator itself flowing coolant properly (this is suspect since turning on the heater helps the situation).
Is the water pump flowing properly?
You dont by any chance have larger than stock tires with factory gearing do you? This could be contributing to the problem.
Has the cooling system been properly bled of all air, preferably with a vacume bleeder

 

[Willow]

Just a few items to check, since it overheats at high speed/high rpm the fan shouldnt be affecting things.
Do you have a larger than stock bumper or a winch blocking airflow in the front?

No

Is the radiator itself flowing coolant properly (this is suspect since turning on the heater helps the situation).

How do I check that?

Is the water pump flowing properly?

How do I check that?

You dont by any chance have larger than stock tires with factory gearing do you? This could be contributing to the problem.

no

Has the cooling system been properly bled of all air, preferably with a vacume bleeder

No...how do I do that?

 

[tbplus10]

Bleeding the system can be done by going to your local Auto Zone or Napa and seeing if they have a radiator pressure check/Bleeder kit for loan or rent.
Follow the normally included instructions.
If there arent any included instructions the kit contains different caps to put on the radiator and or resevoir then you draw a vacume which should pull out any air in the system. Sometimes its easier if you park the vehicle with the front end raised a little and make sure you have the heater turned on to allow flow through the system.
Radiator and water pump flow will probably need to be checked by a shop that has proper equipment. Many skilled mechanics can check the flow by pulling the cap and watching the water at idle but this isnt a tried and true method and can at times lead to mis diagnosys.

 

[Willow]

Thank you! I will try bleeding the system first and take it from there.

 

[j cat]

Thank you! I will try bleeding the system first and take it from there.

the proceedure to purge air from the coolant system with these vehicles is to remove the coolant pressure cap at the plastic coolant fill container when the engine is cold. the start engine and continue to run engine until it is at normal operating temp. then increase RPM to 2000 and hold for about 30 seconds. repeat a few times. if you had air in the system the coolant level will drop.

the other reason you may have overheating during warm/hot weather is a defective coolant pressure cap. if you find when it over heats the coolant hoses are not hard/pressure in them then this is what happens. reason is when NOT under pressure the coolant will boil. when that happens the water pump cannot pump air bubbles and then the over heating.

if you lived in a very high elevation this is more so an issue that the coolant system must be under pressure. since the lower the pressure the lower the temp that the coolant will boil.

now another thing that causes air bubbles would be exhaust gases entering the coolant system . that would be a bad day.

 

[Willow]

OK...checked to see if hose gets hard when hot...it does get harder (I can squeeze a bit so not sure if that is correct or not). Went and rented a pressure tester from auto zone...I can't get it to seal. I am using the adapter that does fit. The instructions inside are pretty useless. At first thought faulty tool...then went back and they gave me a new one in box...now that makes some noise when you pump but no pressure build up. I am sure I am not doing something right as it does hold at least some pressure (I tried to take cap off before it was cool enough and it was boiling and going trough overflow when I loosened). Guess I will do a video search for a test being done to figure out what I am doing wrong. Now when I pump it...what should I pump it up to? I assume at some point I need to start vehicle...when? How long to run? Maybe all that will be int he video. Sigh- a mechanic I am not.

- - - Updated - - -

OK...not having any luck finding more info to see if I hooked this up wrong. From the single photo I saw of one hooked up to a radiator...looks the same as what it did when I had it hooked up to my truck...so why no pressure building when I pump it?

 

[tbplus10]

Should be drawing a vacume, not building pressure.

 

[j cat]

call an Auto Zone in your area and ask if they can help with the pressure tester you have for proper procedure . If with proper hook up/testing no pressure then you now know why it has this problem. finding the leak can be tough especially if you have a head gasket leak. also the water pump gaskets are a well known leak with these.

 

[Willow]

OK...I was putting in on right...the problem was no seal because of the overflow...when I pumped it- air coming out of the overflow tube. Pinched the tube and pumped up to 15 lbs and it held....didn't budge in 10 mins. Thinking cap not allowing pressure to build so when I brought kit back I bought a cap. Will find out tomorrow if that fixed it. If not- freind said to take off thermostat and run without it and see if I still have issue. If so- I would assume thermostat bad (guess it is possible to get 2 bad ones). If not...guess the next step would be to replace radiator (since pulling it out and having it acid washed will cost me anyhow- may as well replace it)?

- - - Updated - - -

Should be drawing a vacume, not building pressure.

All i know is you pump it until the gauge reads 15 lbs...I assume that is pressure and not vaccuum...I could be wrong though.

 

[tbplus10]

Ok you were pressure testing the system for leaks, if your bleeding the system of air you draw vacume.
Many shops no longer boil out radiators, one reason is all the plastic parts, another is its just as cheap to replace the radiator.

 

[j cat]

OK...I was putting in on right...the problem was no seal because of the overflow...when I pumped it- air coming out of the overflow tube. Pinched the tube and pumped up to 15 lbs and it held....didn't budge in 10 mins. Thinking cap not allowing pressure to build so when I brought kit back I bought a cap. Will find out tomorrow if that fixed it. If not- freind said to take off thermostat and run without it and see if I still have issue. If so- I would assume thermostat bad (guess it is possible to get 2 bad ones). If not...guess the next step would be to replace radiator (since pulling it out and having it acid washed will cost me anyhow- may as well replace it)?

- - - Updated - - -


All i know is you pump it until the gauge reads 15 lbs...I assume that is pressure and not vaccuum...I could be wrong though.

sounds good now that it may just be a bad cap and that would be a cheap fix.

it is possible you got a bad thermostat. but if the temp is bad with all 3 thermostats you had in there, with the exact same issue I doubt it.

 

[RayVoy]

I agree with [MENTION=39185]j cat[/MENTION], 3 bad t-stats is not a likely scenario. The cap may be the problem, but it works at slow speeds and driving around town. That's when it should be overheating, highway speed should be "driving" sufficient cooling air through the radiator to keep it cool even if the fan wasn't working.

Are you carrying any heavy loads, or towing?

 

[j cat]

I agree with @j cat, 3 bad t-stats is not a likely scenario. The cap may be the problem, but it works at slow speeds and driving around town. That's when it should be overheating, highway speed should be "driving" sufficient cooling air through the radiator to keep it cool even if the fan wasn't working.

Are you carrying any heavy loads, or towing?

the cap if bad will create this condition at all speeds with the higher temps. also the higher you go in elevation the more so this will occur .

when on the hyway your loading up the engine much more than driving @ 30MPH.

if he had a bad fan clutch this is more vehicle speed . at slow speeds the engine would run hotter than hywy speeds.

 

[SEMiller]

I had an overheat condition yesterday while sitting in traffic, so I turned on the heat up all the way and got off the road until it cooled off. I checked the coolant which was low and added more. In addition to being low on coolant what I thought was curious was the fact that I didn't hear the fan running like I sometimes do just while driving around. I wonder what that was all about.

 

[j cat]

I had an overheat condition yesterday while sitting in traffic, so I turned on the heat up all the way and got off the road until it cooled off. I checked the coolant which was low and added more. In addition to being low on coolant what I thought was curious was the fact that I didn't hear the fan running like I sometimes do just while driving around. I wonder what that was all about.

if you were low on the coolant you most likely have a leak. check the water pump area for leaking at the engine pump gaskets also the heater hoses etc..

 

[RayVoy]

the cap if bad will create this condition at all speeds with the higher temps. also the higher you go in elevation the more so this will occur .

when on the hyway your loading up the engine much more than driving @ 30MPH.

if he had a bad fan clutch this is more vehicle speed . at slow speeds the engine would run hotter than hywy speeds.

Yeah, I agree j cat, that's why I said "but it works at slow speeds and driving around town."
What I find strange, is that blowing air across the heater core is enough to bring the temps back to normal. That's a small core and a small amount of air to fix the problem; not to mention, the small hose capacity that feeds the heater core.

I wonder if the gauge is reading correctly.

what I thought was curious was the fact that I didn't hear the fan running like I sometimes do just while driving around..

I assume, he is talking about the radiator fan. If he can hear it, usually indicates a problem. If the clutch is working correctly, the fan should not make a lot of noise.

I'm suspecting the fan clutch needs to be replaced. Or, perhaps the fan clutch relay may be failing from time to time.

 

[Willow]

OK...cap did not fix it (knew that would be too easy). Stopped at the repair shop I use...they think air flow issue and suggested I pressure wash the front of the radiator even though they said it appeared reasonably clean, said bugs can get in there and block the air flow. So after work, stopped at a car wash and blasted it for about 15 mins. sticking wand into the grill. Did not fix issue. Now I do have a spectre air intake system on it.....that I put on almost a year ago...but I was having issue before that was put on.
RayVoy- no, not towing or carrying anything (other than my tiny little self).

TBPlus...not sure what drawing air out of the system would do as I had to pinch the overflow hose just to get vacuum....soon as I would unpinch hose...air would come in as well as when I took off the pump and replaced cap. I did not see any options for vacuum on this pump either....it was a pretty simple kit from AutoZone.

Jcat- I agree. I doubt it is the thermostat. Just saying what my friend suggested to try- I am running out of things to try here. BTW I am a she

Someone mentioned defective gauge? Now that may be a possibility. I have been having issue with my fuel gauge (been writing down how many miles to put in gas so I don't run out- I figure at 16 mpg to be on safe side and when I fill up I end up being pleasantly surprised). BUT if that was the case would it not also do that in cooler weather and not drop when I turn on heat?

What would you all try next? I am now scratching my head.

 

[SEMiller]

if you were low on the coolant you most likely have a leak. check the water pump area for leaking at the engine pump gaskets also the heater hoses etc..

I took a quick look under the hood and didn't see any wetness around the water pump or hoses. The truck has to go in for an inspection in August, I'll have my mechanic do a coolant flush and check that out.

 

[RayVoy]

Hi Willow, looks like someone tagged along on your thread, I answered him (?) in my previous post thinking it was you.

But, that answer may fix your problem as well. I suggested a problem with the radiator fan clutch. He could hear his (not normal), but yours may not be working, therefore the fan does not engage and the fan blades don't spin.

It should throw a check engine code and light the CEL (check engine light), but it may be worth a try.
With the engine turned OFF, try to turn the radiator fan blades. Try it when engine is hot, and when cold. Don't force it, you could bend a blade.