I’ve got a 2003 with a 3.4L.

My problems that started flashing the overtemp warning along with erratic temperature gauge swings.

At first I thought it was just low on fluid but I topped it off and still had problems.

This is what I have done.

I flushed the system.

Replaced; radiator cap, water pump, thermostat, all bypass hoses, and installed screw type clamps.

I checked and had good flow throught the heater core, bypass tube and engine with the water pump off.

I have pressure tested and the system holds 15# for over an hour.

There are no external fluid leaks.

There is no increase in oil volume or milky color in the oil or under the cap.

Transmission fluid looks good.

No fluid leaks in the car on passenger side under heater core.

Here's the weird stuff.

Sometimes the heat works and sometime it does not. To me it almost seems as if the fluid is low and not getting to the heater core. I top off the system by filling the radiator to the top and fill the flush connector which is in the hose from the heater core. If the heat works the temp stays at 195. If it does not, then sometimes the temp goes to about 205, and then the heat may work and the temp will fall to about 175. Sometime it will climb to about 250 and then the heat works and the temp drops to 175 to 195. Sometimes, usually when it's cold, it will climb to 260 and the warning is triggered.

I do seem to have to top off the radiator after it cools, I don't know if this is normal when purging the system of air, but it seems excessive. I thought that the fluid would be sucked back into the radiator from the reservoir I cleaned and refilled the reservoir tank. Tested the tube to the radiator for leaks, none found, and replaced the clamps with screw type clamps to prevent any fluid or air leaks.

No excessive white smoke from the exhaust or coolant smell.

When I refilled the system I followed the steps in the All Data Online:

Filling Procedure
• Tools Required
• J 23688 Coolant and Battery Fluid Tester
Notice: Refer to Fastener Notice in Service Precautions.
1. Close the radiator drain ****.
• Tighten the radiator drain **** to 2 Nm (18 inch lbs.) .
2. If the engine block drain plug was removed, perform the following:
2.1. Apply pipe sealer to the drain plug.
2.2. Install the drain plug.
• Tighten the drain plug to 22 Nm (16 ft. lbs.) .
3. Lower the vehicle.
4. Open the cooling system bleeder screws. Important: Use a 50/50 mixture of DEX-COOL antifreeze and deionized water.
5. Slowly fill the cooling system with a 50/50 coolant mixture.
6. Close the cooling system bleeder screws
7. Install the coolant pressure cap
8. Start the engine.
9. Run the engine at 2,000 - 2,500 RPM until the engine reaches normal operating temperature.
10. Allow the engine to idle for 3 minutes.
11. Shut the engine off.
12. Allow the engine to cool.
13. Top off the coolant as necessary.
14. Inspect the concentration of the engine coolant. Using the J 23688.
15. Rinse away any excess coolant from the engine and the engine compartment.
16. Inspect the cooling system for leaks.

I did not drain the block.

I've searched the web for "no heat 3.4L" and found allot of 3.4L engines have problems like mine. It seems when the engine is cold, a crack in the head or the head or intake gaskets can leak, which allows air from the cylinders into the coolant system. This in turn causes loss of heat.

I suspect I’ll have to have the top end repaired. Is this over the head of the average DIY mechanic?

Any idea on how much this would cost to fix worst case, which I’m guessing is a blown head gasket?

Thanks!

 

No BS, it is alot of work if you've never done it, BUT it can be done if you are determined enough.

I would recommend all the gaskets while you are ripping it apart. Take off the intake, LIM, valve covers, rockers, pushrods, exhaust manifolds, and finally heads.

 

Also you will probably need to take out the alternator and coil packs. I haven't worked on this engine yet.

I would also pull the battery and air intake just for more room.

Finally if you have never done this before, get around 20 small boxes to hold bolts and nuts in and label them. You can typically get some from Home Depot, Menards, Lowes, etc for when they stock hardware. Look for sizes that will hold a system together. Usually about around 1'x1'x1' should be good.