1995 Monte Carlo overheating

viijamesiiv · 06-27-2009, 07:58 PM

Ok here is my issue

I have a 95 Monte carlo with a 3.1 engine. It started overheating but only when i was driving at high speeds. I took it to about 4 mechanics and no one could properly diagnose it. I have had a chemical test done to the radiator to show if emissions are getting into the coolant. That checked out ok. They have overlooked the entire motor and could not find and signs of leakage that would relate to a gasket. There is no coolant getting into the oil at all. I have had the following replaced: Water Pump, Thermostat, Radiator, Fan Relay. I have even hard wired that fan to stay on constantly.

The Radiator was a help but for only about 3 weeks. After that, it began to run rough and stall out on me. Sometimes not starting without pumping the gas, even though its fuel injected. Then it started to redline at lower speeds and is now not drivable. Im not sure where to go from here. Does anyone have a suggestion before I have to resort to the dealer?

**octaneman** · 06-29-2009, 12:49 PM

Hi viijamessiiv

There is a coolant circulation problem even though the water pump and radiator has been replaced. Considering that you have replaced everything, do a complete engine block flush to clear out the crud that maybe blocking the coolant passages from the engine to the heater core. Take temperature readings from the upper and lower radiator hoses including the heater core hoses and feel if there is a substantial difference in temperature between them. If you do feel a difference, then the water jackets are blocked. Have you checked the coolant fan sensor ? Is there a bleeder screw on top of the thermostat housing to bleed the system ? If so did you bleed the system ?

viijamesiiv · 06-30-2009, 01:05 AM

I talked to the mechanic that replaced that cooling system parts and he says he bled the cooling system. Although the "Low coolant" light is lit up on my dash, there is plenty of coolant. If there in fact may be a blockage, what would cause the rough idling and stalling? This started happening just before it began to redline (completely overheating).

**octaneman** · 06-30-2009, 11:26 AM

The low coolant light can be either a bad sensor or the wires are grounding somewhere. When the engine starts to overheat the temperature sensor is giving signals to the computer to correct the air/fuel ratio, but it also takes readings from other sensors and attempts to compensate the difference throwing the engine off balance. The computer only knows what the sensors tell it, and when the readings conflict with its internal programming the computer will go into limp home mode telling the user there is a problem with the sensors and it warns the driver with the check engine light. If the engine has seriously overheated, then it's not uncommon to find the coolant temperature sensor for the ECM to be burned out. The coolant sensor can be fooling the ECM that the engine is dead cold and send false readings causing the engine to rev high even though its hot.

06-27-2009, 07:58 PM	#1 (permalink)
viijamesiiv Registered User Join Date: Jun 2009 Posts: 2 OS: Mac OS	1995 Monte Carlo overheating Ok here is my issue I have a 95 Monte carlo with a 3.1 engine. It started overheating but only when i was driving at high speeds. I took it to about 4 mechanics and no one could properly diagnose it. I have had a chemical test done to the radiator to show if emissions are getting into the coolant. That checked out ok. They have overlooked the entire motor and could not find and signs of leakage that would relate to a gasket. There is no coolant getting into the oil at all. I have had the following replaced: Water Pump, Thermostat, Radiator, Fan Relay. I have even hard wired that fan to stay on constantly. The Radiator was a help but for only about 3 weeks. After that, it began to run rough and stall out on me. Sometimes not starting without pumping the gas, even though its fuel injected. Then it started to redline at lower speeds and is now not drivable. Im not sure where to go from here. Does anyone have a suggestion before I have to resort to the dealer?

06-29-2009, 12:49 PM	#2 (permalink)
octaneman Mentor Home Support, Gearhead Automotive Center Join Date: May 2009 Posts: 549 OS: WINXP	Re: 1995 Monte Carlo overheating Hi viijamessiiv There is a coolant circulation problem even though the water pump and radiator has been replaced. Considering that you have replaced everything, do a complete engine block flush to clear out the crud that maybe blocking the coolant passages from the engine to the heater core. Take temperature readings from the upper and lower radiator hoses including the heater core hoses and feel if there is a substantial difference in temperature between them. If you do feel a difference, then the water jackets are blocked. Have you checked the coolant fan sensor ? Is there a bleeder screw on top of the thermostat housing to bleed the system ? If so did you bleed the system ? Last edited by octaneman; 06-29-2009 at 01:07 PM.

06-30-2009, 01:05 AM	#3 (permalink)
viijamesiiv Registered User Join Date: Jun 2009 Posts: 2 OS: Mac OS	Re: 1995 Monte Carlo overheating I talked to the mechanic that replaced that cooling system parts and he says he bled the cooling system. Although the "Low coolant" light is lit up on my dash, there is plenty of coolant. If there in fact may be a blockage, what would cause the rough idling and stalling? This started happening just before it began to redline (completely overheating).

06-30-2009, 11:26 AM	#4 (permalink)
octaneman Mentor Home Support, Gearhead Automotive Center Join Date: May 2009 Posts: 549 OS: WINXP	Re: 1995 Monte Carlo overheating The low coolant light can be either a bad sensor or the wires are grounding somewhere. When the engine starts to overheat the temperature sensor is giving signals to the computer to correct the air/fuel ratio, but it also takes readings from other sensors and attempts to compensate the difference throwing the engine off balance. The computer only knows what the sensors tell it, and when the readings conflict with its internal programming the computer will go into limp home mode telling the user there is a problem with the sensors and it warns the driver with the check engine light. If the engine has seriously overheated, then it's not uncommon to find the coolant temperature sensor for the ECM to be burned out. The coolant sensor can be fooling the ECM that the engine is dead cold and send false readings causing the engine to rev high even though its hot.