Question about 2001 Chevrolet Silverado 2500HD

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Air pocket in coolant system

Fan blows good but no heat

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  • swissmade59 Feb 28, 2009

    ford /focus 2002 put in a thermostat can't get air pocket out what now

  • Richard Delahant May 11, 2010

    try having the system bled of any air build up. There are 2 other things to have checked----- there should be a vacuum operated actuator valve that opens the heat vent door, and the heater control valve. The acuator valve is under the dash usually up and behind the ac ducts.



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Loose Radiator or coolant cap in cold and have the car idle for five minutes with out the cap, or have the car idle for 10 minutes, wile running remove cap, let air pressure out and put cap back, do it 3 or 4 times till all air is out...

Posted on Jan 22, 2009


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Heater not heating but fan working what could be the cause

You may have an air lock in the cooling system or your heating control valve may be stuck/broken cable

Apr 02, 2016 | Cars & Trucks


How to inspect,diagnose and repair minor over heating problem for under 2 hours.

Copyright © by Mustgo on Dec 2009

How to inspect,diagnosis and repair minor over heating problem in under 2 hours.

Thanks for viewing my Fixya tip post.

My goal is to solve the most common over-heat,running hot on stop and go traffic and intermittent cabin heating problem (no heat)

The target audience is DIY'er who has a car that's just starting to over-heating and has about 2 hours to ran though my check list.


The first part is basic universal safety.

Follow by steps the required to fully diagnose the root cause of the problem.

Example:air pocket in coolant system VS worn water pump VS blown head gasket.


Follow by THE FIX.


If you are just getting the initial sign of over-heating then you will be able to replace the thermostat2_bing.gif,gasket,black RTV,coolant mix and 50/50 mix coolant temperature sensor and get back on the road for under $80.

For those who has leaks on the radiator,water pump the repair cost will be much higher.

Losing coolant and having WHITE smoke coming out of the tailpipe after 15 minutes of warming up is a sign of blown head gasket.
This is an internal head gasket damage and the engine head(s) must be remove to do a head gasket job.


My tip is for folk what are encounter over-heating on the first week.
Hopefully under 3 times of over-heating.

Repeat over heat will warp the aluminum head(s),blow out radiator hose(s) and radiator.




MAKE SURE safety goggles are on at all time.


You will spill some coolant during this air pocket purge test.......BE KIND TO THE ENVIRONMENT and ANIMAL please clean up after the test!


When the car is completely cool,check the electric fan(s) for smooth rotation.

Make sure there is not wobble movement or touching surrounding plastic.

Clean/check/change the thermo/temp sensor,contacts and wires.

CRC Electrical Contact Cleaner is the ideal chemical to speed up the cleaning job.

Clean the metal contacts on fan relay,inside the relay socket and fan socket.

Follow the sensor all the way to the firewall to make use it's in perfect condition.

Inspect other wiring for cut,and exposed wiring.

Use 3M high temp. electrical tape to protect damaged portion of the wire.



THIS IS A 30+ minutes JOB.

The longer you can monitor the coolant system will give you a better idea of the condition of the coolant system.

Excavate air pocket in coolant system / check for head gasket leak

Air pocket can be trap inside the coolant system.

The water pump's turbine / fins is totally ineffective when there is not coolant surrounding the water pump.

This test will kill two birds with one stone.

Most radiator shop charge $75 just to excavate / air purge the coolant system.


Top of the coolant reserve tank to the COLD / COOL / LOW level.

Put the front end on a pair of ramp or park your car on a VERY STEEP HILL (radiator facing top of the hill) .

Keep the coolant reserve tank cap in a safe location.

The goal is to lift the vehicle higher to monitor the air pockets and let it escape.

The radiator should be 8-20" high from the stationary position to let the air pocket to escape.

Let the car ran and start monitor the temperature.

Monitor for air pockets escaping from coolant reserve tank.

Small amount of bubbles is OK at 1-5 minute mark

After the thermostat open up at 195-210 F,Electric fan should turn on automatically

If your vehicle has a secondary electrical fan then turn on the A/C and all lights,radio,and electrical items to ensure the fan is operation.

5-12 minute mark or after high idle you should see less bubbles.

If you DO NOT see any in rush of bubbles when thermostat opening between the 5-12 minutes mark then the maybe partially stuck or rusted badly inside the thermostat hosing.

Give the thermostat housing few gentle taps.
(follow the TOP large radiator hose to the top portion of the engine)

If you see larger bubbles surfacing after 15 minutes then should do a hydrocarbon (HC) dye test to test for potential head gasket leak.

A coolant pressure test is also a must to pressurize the coolant system to locate addition leaks.

Examples:radiator,head gasket,freeze plugs,or water pump

Let engine cold down,lower the car onto level server and top off coolant reserve tank to the TOP / FULL /HOT level.

Start monitor for coolant lost everyday.



If the radiator cap is over 5 years old or rusted badly then change it.
The spring can be weaken and will not hold pressure.

I recommend the thermostat that has a relief pop-let to reduce the change of burst radiator and coolant hoses.

Thermostat,gasket and black RTV is not expensive and it should be change every 4 years or 48,000 miles.

A coolant flush is require every 2 years or 24,000 miles.
Check your service log for the last coolant flush.

Low heat condition is cause by combination of stuck thermostat,low coolant level,dirty coolant system and worn turbine / fins on the water pump.

If the water pump has over 85,000 miles on it then water pump can SLOWLY leak into the time belt cover.

The turbine/fins on the water pump can erode badly after 96,000 miles.

Monitor coolant level and check for water pump,radiator,coolant hose leaks.

Place a larger cardboard under the radiator,water pump or timing belt cover. Monitor the coolant drip and inspect the problem area accordingly

Visual Inspect your coolant reserve tank for bubbles when the temp. is near 195F+. (after a long drive) If you see hydrocarbon leaks then you should stop driving the vehicle until a shop do a pressure test and dye tests.


If my post is helpful to you then please rate it!

on Dec 05, 2009 | Honda Civic Cars & Trucks

1 Answer

The heat blows cold and hot. Is it the resistor module or the themostat

The resistor controls fan speed, not temp.
If the heat comes and goes, it could be the thermostat, or the radiator could be low on coolant, or have air pockets, or one of the blend doors may not be working correctly.
The blend doors direct air thru the heater core and the vents.

Dec 20, 2012 | 2003 Chrysler Town & Country

1 Answer

My heater is not blowing hot air consistantly...the fan works, the ac works, but the heat blows hot sometime and not others

Sounds like you have an air pocket trapped in the coolant system.This will cause intermittent heat and especially at idle with little water pump circulation.Try to remove the reservoir cap when not under pressure and start the engine.allow the engine to reach operating temp and allow any trapped air to escape for about 30 minutes.turn off the engine and allow it to sit without the pressure cap on for around 5 minutes.Top off coolant as needed and replace the cap.Let's see what happens from there.Hope this helps,
Kenneth R.

Oct 08, 2010 | 2003 Volkswagen Golf

3 Answers

04 sentra 1.8 over heats after a highway drive. Pull off the highway and come to light and needle shoots to just under H! Start to drive and needle drops right away. Changed thermostat, did two rad...

Air pocket need the thermostat housing.

Air is not a good conductor of heat.

Park you car on a hill and let the air pocket to work itself out to the cooling system.

A shop will charge $65+ to purge the air out.

Aug 11, 2010 | 2004 Nissan Sentra

3 Answers

Would the heater control valve malfunctioning make the engine overheat blowing hot air out the heater one moment,then not blowing the hot air, temp gage spikes 225 plus. The motor takes awhile to heat up...

Heater control valve malfunction will not cause engine to overheat unless coolant is leaking externally...Overheating going down the road can be the result of a few different things...Partly clogged radiator...Insufficient air flow due to possible fan problem...External coolant leak...Make sure fans are operting properly and have cooling system pressure tested for leaks...Gaining and losing heat on the inside of the vehicle usually means system is low on coolant but you must find out where coolant is going

Jan 06, 2010 | 2004 Chevrolet Impala

2 Answers

Running Hot

You may want to reconsider if the fan is working at it's full potential.It seems when the vehicle is moving the extra air flow compensates for the fan not blowing hard enough.Check for radiator obstructions such as leaves and debris.And check for small leaks.Also there may be an air pocket in the system which can still seem like the system is full.With vehicle cold take off radiator cap and run vehicle.Turn on heat to highest setting (blowing).When vehicle reaches thermostat rated temperature(opened thermostat) you will see coolant go down in radiator.Fill radiator while the engine rpm's are up (have someone hold the throttle to where the rpm's are at about 1800) then put on cap before returning to idle.This should remove the pocket if there is one

Sep 16, 2009 | 2005 Chevrolet Trailblazer Ext

1 Answer

Honda civic 1998 over heating. cooling fan problem? Where are the fuses for that. Thank you

Most likely you have a bad thermostat is stuck and not letting coolant to flow to your radiator. check your coolant level if is normal replace the thermostat NOTE: if you live air pockets on your cooling system then also cause to over head when adding new coolant open the bleeder valve if you cant find it just add coolant whit the engine running when the new thermostat open will release the air pocket and you will see a sudden drop of you coolant level, then add more on till the radiator is full again. never drive your car for long is your engine is over heating that will cause a blown head gasket and mayor repairs. if your on the street and just notice than your car is over heating turn your A/C off set it on heating maximum fan max heat and of coarse roll down all your windows. it be real hot for you but that will save your engine. the heater core on your car is like a baby radiator and bypass the engine thermostat that will help to cooled down a lot . hope this help you and good luck.

Jun 02, 2009 | 1998 Honda Civic

1 Answer

Heater in 1998 Ford Taurus

When u flushed the radiator, what did u find? Was the old coolant dirty, rusty, sediment in it? What u describe sounds like the core is plugged up w/ junk. This would be my 1st choice of the problem, especially if the coolant was rusty, cruddy, as described above. It wouldn't be an air pocket (after a couple of years). Some cars do have a valve that opens and closes to allow the hot coolant into the core for heat, or a flap door that opens to allow the fan to blow air thru the core for heat, but the fact that this started when u flushed the system leads me to believe it's a plugged up core. U could try to flush the system again, make sure the heat is on when u do, so u have circulation tthru the core to help flush it out. let me know how u make out. good luck!

Oct 23, 2008 | 1998 Ford Taurus

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