All problems caused by engine coolant bypass valve

There could be a few possible causes for the rear heater not blowing hot air in your 2003 Chevrolet ASTRO van. Here are a few things you could check:

1. Make sure that the rear heater control valve is fully open. This valve is located near the heater core and controls the flow of coolant to the rear heater.
2. Check the coolant level in the radiator. If the coolant level is low, the heater may not be able to produce hot air.
3. Check for any leaks in the coolant system. If the system is leaking, it may not have enough coolant to produce hot air.
4. Check the thermostat. If the thermostat is stuck closed, it may not be allowing enough coolant to flow through the system to produce hot air.

If these steps do not help, it is possible that there is a problem with the heater core itself, or with other components of the heating system. It may be necessary to have a mechanic diagnose and repair the issue.

In the old days engines used to be built with a bypass cooling system, either by hose or via an internal coolant port. In those days lots of vehicles were produced where the heating and ventilation system was optional and where a heater was fitted the coolant flow would be shut off by a valve during the summer.

Where no heater was fitted or when the heater valve was closed and when the thermostat was closed, the amount of coolant circulating in the engine would be minimal and there would be hardly any circulation through the cylinder head resulting in many problems - hence the need for a bypass system that would allow coolant to circulate through the cylinder block and cylinder head and back into the water pump.

When constant flow heaters were introduced, where heated coolant flows constantly through the heater and the temperature controlled by air mixing, the bypass system became unnecessary and was mostly deleted as it slowed warm up and the flow through the heater was an efficient alternative.

Basically, if there is a bypass it is acceptable to clamp or otherwise blank off coolant flow to the heater.

If there is no bypass the coolant flow must be maintained when isolating the heater, which usually means joining the disconnected hoses together.
As it is a dual heater vehicle, the rear heater will provide the bypass duty so you could simply clamp the hoses to the front heater if it is inconvenient to disconnect them.

Have you done basic tests, such as fuel pressure? Coolant temp sensor? Crank sensor?

Engine or hydraulic system overheating Coolant system low on coolant in 6020, 6030, 6030 Premium, 7020, 7030 and
7030 Premium Series Tractors.

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Symptoms
After several hours of work, warning system indicates hot engine coolant or hot hydraulic oil.
Situation or Problem
Coolant level in reservoir is between the "MIN" and "MAX" range but engine or hydraulic system is overheating.
Summary
Air is entering cooling system, hindering coolant flow. Check coolant level. Fill to the "MAX" line on the coolant reservoir.
Bleeding Cooling System:
The bleed valve (see Operator's Manual for location) on the radiator must be closed when the tractor is operating. Open the valve when coolant is drained or filled. If the bleed valve is left open, coolant will internally bypass between the low temperature circuit and engine high temperature circuit causing overheating. When bleeding the system, open the bleed valve and run the engine with no load for 5 minutes at 1700 rpm. Then shut engine off for 5 to 10 minutes before closing the drain valve. Check the coolant level. If level is below the "MAX" fill line, repeat this procedure until coolant level stays at the "MAX" line.

What engine 2.2 or 2.4 ?
Important: On vehicles equipped with the 2.4L engine, open the coolant air bleed valve. The coolant air bleed valve is located on the top of the thermostat bypass pipe/heater pipe assembly. Close the valve once a continuous stream of coolant is expelled from the valve.
Does the cooling fan come on ?
Notice: When adding coolant, it is important that you use GM Goodwrench DEX-COOL™ coolant. If coolant other than DEX-COOL™ is added to the system, the engine coolant will require change sooner: at 50 000 km (30,000 miles) or 24 months.
Close the radiator drain ****. Remove the drain hose.
If previously removed, install the engine block drain plugs.
When installing the drain plugs, use pipe sealer GM P/N 12346004.
Important: On vehicles equipped with the 2.4L engine, open the coolant air bleed valve. The coolant air bleed valve is located on the top of the thermostat bypass pipe/heater pipe assembly. Close the valve once a continuous stream of coolant is expelled from the valve.
Fill the surge tank to the base of the filler neck.
Start the engine with the pressure cap off. Let the engine run until the upper radiator hose starts to get hot.
If the coolant level in the surge tank is low, add the proper mix of coolant until the level reaches the full cold line.
Important: After servicing the cooling system, and if the vehicle is equipped with an intermittent low coolant light, an occasional low coolant light may be encountered during some extreme driving maneuvers. This complaint should be eliminated by removing the surge tank cap and adding coolant to a level just at or above the full cold line when the system is cold.
Install the cap onto the tank with hand tight pressure.

Check for leaking vaccum lines from the engine intake manifold. If no leak, test the IAC motor and clean out the air bypass passages per instructions below. Let me know if this doesn't solve the problem or you have any questions.

OPERATION
The Idle Air Control Bypass Air (IAC BPA) valve consists of an idle air control valve and a bypass air valve. The bypass air valve functions during cold engine conditions to increase engine idle speed. It consists of a thermowax bead and a valve.
Engine coolant is directed around the thermowax, which opens and closes the valve. During cold engine operation below 140°F (60°C), the thermowax is contracted enough to allow the valve to open. As the coolant heats, the thermowax begins to expand. When the coolant reaches temperatures above 140°F (60°C), the thermowax expands and closes the valve.
The valve controls the amount of throttle valve bypass, which ensures a smooth idle under all engine operating conditions.

1. When the engine is cold, air flows through the valve during all modes of engine operation, to maintain the factory set idle speed.

TESTING See Figures 1, 2 and 3 (if you don't have an ohmmeter, skip this test)

1. To check the Idle Air Control (IAC) valve resistance, unplug the IAC valve connector.
2. Connect a high impedance Digital Volt Ohmmeter (DVOM) to the terminals.
3. Measure the resistance.
4. The resistance should be 7.7-9.3 ohms.
5. If the resistance does not meet specification, replace the IAC BPA assembly.

Fig. Fig. 2: Connect an ohmmeter to the IAC valve; the resistance should be 7.7-9.3 ohms

At this point, if your IAC checks good, I recommend you take out the 4 screws seen above, remove the motor, and clean out the air passages/valve with carb cleaner. Also remove the big (3 inch diameter) hose from the throttle and clean out the throttle body, if dirty.

If the IAC tests bad, go to the removal and installation directions below.

The next test requires a scanner. If you don't have a scanner, skip this test.

1. To check the BPA valve function, remove the BPA valve from the engine.
2. Wait until the valve reaches room temperature. When the valve is cold, blow through the air inlet and verify that air flows freely through the valve.
3. Heat the valve with a hair dryer; the air valve should move out and block the passage.
4. If the valve does not function as specified, replace the IAC BPA assembly.
5. To test the solenoid, connect a scan tool to the Data Link Connector (DLC).
6. Turn the key ON and enter the simulation test.
7. Access the IACV Parameter Identification (PID) and turn the dial to cycle at 75 degrees.
8. Listen for the IAC solenoid to click when using the simulation test.
9. If the solenoid clicks it is working properly.

Fig. Fig. 3: Idle Air Control Bypass Air (IAC BPA) valve assembly components

REMOVAL & INSTALLATION

1. Disconnect the negative battery cable.
   CAUTION

Never open, service or drain the radiator or cooling system when hot; serious burns can occur from the steam and hot coolant. Also, when draining engine coolant, keep in mind that cats and dogs are attracted to ethylene glycol antifreeze and could drink any that is left in an uncovered container or in puddles on the ground. This will prove fatal in sufficient quantities. Always drain coolant into a sealable container. Coolant should be reused unless it is contaminated or is several years old.

1. Drain the coolant until it is at a level below the Idle Air Control Bypass Air (IAC BPA) valve.

The lower coolant line should be disconnected after the valve is separated from the upper intake manifold.

1. Tag and disconnect the upper coolant hose from the valve.
2. Unplug the valves electrical connector, then loosen the two nuts and two bolts attaching the valve to the upper intake manifold.
3. Pull the valve from the manifold and disconnect the lower coolant line from the valve.
4. Remove the valve and gasket from the engine.
   

To install:

1. Use a scraper to clean any old gasket material from the valve mounting surface.
2. Install a new gasket and connect the lower coolant line to the valve.
3. Install the valve and its retainers. Tighten the nuts and bolts to 71-88 inch lbs. (8-10 Nm).
4. Engage the valves electrical connection and the coolant hoses to the valve.
5. Fill the cooling system and connect the negative battery cable.

Does your engine overheat? Could be a thermostat that is stuck, let me know with some clarification and i can help ou better. Thanks

Over heat is caused by poor circulation of coolant. This problem can be: 1- The thermostat is not opening ( bad) causing coolant stagnant. 2- Water pump is bad, not circulate coolant. 3- Radiator is clogging up. It is full but water can not going through small clogging up tubes inside to have heat dissipated through the fines.
Since you also have no heat then I think the bad coolant causing the heater core clogged up also, unless the heater valve has a problem not allowing cooling flowing through the bypass hose to the heater core. Correct all 3 things above then you should be OK. Good luck.

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.

Yes this sounds like the throttle body warmer thing-- on a LR that isn't in a cold climate you can just bypass it. I did on my DII in california.