Car overheating

1998 Pontiac Sunfire 2.2L

Purchased this car off craigslist. Has several issues but am trying to resolve them myself. The car overheats but is NOT losing coolant. I have since replaced the water pump, radiator, radiator fan motor, and radiator hoses. Car still overheats. It does not seem to be rushing around in the coolant tank. Could it be blocked somewhere? I was thinking about bypassing the heater core to see if that would solve the problem?

No oil in the water, no water in the oil. Coolant does not get low. Could it be possible the head's blown? Nothing indicates that. Car runs like a dream.

Engine codes... several of them but most have been fixed I think. P0141 which was the oxygen sensor code. Replaced it but light came back back on for it. The others went away though. Replaced cam position sensor, and the crank position sensor and those codes no longer register... just p0141.

Any advice or questions?

>>>>

Speed makes a difference for 2 reasons.
If it overheats at stops or under 30-35 mph, but does not heat up at higher speeds, it indicates a lack of airflow through the radiator, i.e. a cooling fan problem.
If it heats up at highway speeds, but runs cooler at lower speeds,(lower rpm) it indicates a problem with coolant flow.

Have you checked the coolant level again to be sure the coolant is still full, and has not gone low due to the thermostat opening?

Another thing to mention; you say you checked the thermostat and it was opening in boiling water. Is it opening fully? I have had to change thermostats that were partially opening, but still causing a restricted flow and causing overheating. If it is not opening all the way, this could be your problem.

If everything checks out good, call a radiator shop and ask if they have a "block tester" that checks for combustion in the cooling system and have that checked....

Is this a "4" motor(8th digit of VIN)?

If I am going though the trouble of pulling out a thermostat, it's getting replaced(use OEM, there have been some problems with aftermarket).....

A plugged heater core can cause overheating(the core acts as the engine by pass)......Drive the car on the highway, and as the coolant temp needle reaches the 11 o'clock position, turn the selector to vent, full heat(windows open)....continue down the road.....should have about 145-150F heat from vents.....as the engine continues to move towards overheating, does the temp out of the vents drop? If it does, there is either an air pocket being formed or the core is plugged(can be verified by touching the inlet and outlet hoses to the core.....SHOULD be the same temp....if the outlet is cooler, try a reverse flush....

Coolant fan should come on at about 228F.....

Absolutely sure you are not losing coolant? Always check reservoir level when cold.....if this has a radiator cap, check radiator level cold too...if it doesn't have one(the pressure cap is on the reservoir), then just check level in reservoir.....

How to stop Radiator Leak

Locate the leak. Sometimes, you can see steam coming up from the radiator, indicating a pinhole or ruptured seam. Otherwise, wash down the radiator and the hoses with water and start the engine again; as it runs, watch for the leak.


Let the engine cool off. Once you've found the leak, wait a few minutes to take off the radiator cap; otherwise, you could be scalded by hot water or steam.

Plug the leak. Keep in mind that these are temporary fixes and are not meant to be substitutes for a permanent fix - they're meant only to get you to a repair shop. You have a few options; use what you have on hand or can attain most easily:

• Use cold weld epoxy. This is the safest and most reliable option, but it might be hard to find if you suddenly break down. To do this, make sure you have water on-hand before you drain the radiator. After it's dry, apply the cold weld epoxy over the leak. This method will require waiting about two hours for the epoxy to dry.
• Use an egg. One or two eggs will temporarily stop the leak by cooking in the hot water of the radiator. The pressure of the radiator will force it into the leak (if the leak is in the radiator itself and not one of the hoses).
• Use black pepper. Pour a spice-rack-sized container of pepper into the radiator. It will flow to the split or pinhole and will harden like a rock and plug the hole. If you don't have pepper, paprika, cornmeal and mustard powder are acceptable alternatives.
• Purchase a commercial leak repair product. These are widely available in most automotive parts and supply stores. Use these as a last resort; it should be noted that adding any of these types of products to the cooling system of your car can obstruct the flow of water through the radiator, and potentially damage other parts of your car such as plugging the heater core.
• Weld the leak. If you have the expertise and the equipment, you can try to remove the radiator from the car and weld the leak yourself.
• Use duct tape. If the leak is in only on one of the hoses, you can wrap duct tape around it for a temporary fix until you can purchase and install a replacement hose.

Build a vacuum. Remember to install the radiator cap so pressure will build and force the epoxy, pepper or egg into the leak.

Get to a repair shop. A leaky radiator will require a more permanent fix than those listed above. Any additives may be flushed out by high pressure later when a permanent professional repair is made.

Related articles

• How to stop Radiator Leak

  ---