Cooling system mahem! General Cooling System Knowledge will

Hello all! I have a 2000 Daewoo Leganza Automatic DOHC engine type and the cooling system is out of wack. I first noticed it when the heat went out and my incredibly cold Northern Michigan drives became intolerable. I also have a child due to be born in less than a month which makes getting this fixed a top priority. I am adamant about doing the work myself as cash reserves are low right now, and a working knowledge of automobiles is something I’ve always wished to attain. Although I’m no seasoned mechanic and my introduction to automotive systems has just begun, I am mechanically inclined and have learned a lot in the short period of time I've been attempting to tackle this issue. I have obtained a 2,500 page service and repair manual for the vehicle model and year and that has been very helpful. I still short on experience and need some expertise in my corner.

I’ve replaced the thermostat and tested the old one which was working fine and opened around 185 degrees. The vents now blow warmer air into the vehicle’s cabin, but the air temperature is still not substantial enough to suggest that the appropriate fix was made. Because of further investigations towards fixing the heat problem, it has become clear that there is a fault in the vehicle's cooling system. I have performed the written procedures outlined in the service and repair manual to try and pinpoint what part of the cooling system is failing or what else could be causing this issue. I have now exhausted all the diagnosis procedures the book has to offer, and those, which I feel, are most relevant to the problem. Below is a list of systematic symptoms or discrepancies I have noticed during my evaluations of the cooling and HVAC systems. I've tried to categorize them and make them clear and thorough as possible. I'm hoping that someone here can put me on the right track to resolve these issues.

A few items of focus to start with:

1.Coolant appears to maintain a steady flow through the coolant reservoir tank when observed right after starting the vehicle. This is supposed to be an indication that the coolant pump is operational.
2.When the vehicle is cool, there are no apparent leaks in any component of the system.
3.I replaced the thermostat.
4.All the lines in the cooling system appear to warm up correctly before the vehicle is operated and hot air is distributed into the cabin at this time.
5.2 miles into the drive the air introduced into the cabin turns cold.
6.5 to 7 miles into the drive, the temperature gauge begins to fluctuate.
7.After stopping the vehicle turning the engine off coolant is visible on the exterior of the coolant reservoir tank and surrounding areas. A slight hissing noise will sometimes come from the reservoir tank as well.
8.The coolant coming from the engine, located in the thermostat housing is clearly boiling.
9.It seems like the cooling system starts out working just fine. Then as the vehicles being driven begins to malfunction.

Cold engine off, pre-operation:

1.Coolant levels are correct to specifications.
2.No visible leaks in the lines of the cooling system.
3.No visible leaks in the radiator.
4.No visible leaks in the coolant reservoir tank.
5.No visible kinks or collapses in the lines of the cooling system.
6.All hose connections appear secure.
7.Draining the cooling system has shown no signs that the coolant is contaminated with gunk or grime, and is as clear coming out as it is going in.
8.Pressure in the cooling system created by squeezing the upper radiator hose in a pulsating manner is visible as the level of coolant rises and falls in the reservoir tank.

Cold, just started, engine idling, pre-operation:

1.The flow of coolant is apparent when looking into the coolant reservoir tank and the flow rate appears to be what one would expect from the pressure generated by the water or coolant pump.
2.No coolant flow is apparent when squeezing the upper radiator hose just beyond its connection to the thermostat housing unit.
3.The vehicle seems to warm up or reach idling temperatures and an appropriate amount of time.
4.The blower appears to be fully functional.
5.The defroster ventilation mode does not operate. Only a very small amount of blown air will exit through the defroster vent even if the mode dial is set to defroster.
6.The majority of air released through the ventilation system comes through the dashboard. Even if the ventilation mode control dial is set to direct air only at your feet, a steady amount of air will still enter the cabin through the vents located on the dashboard.
7.Both points five and six continue even if the vehicle is in full state of operation or rather being driven.

Warm, engine idling, pre-operation:

1.Upper radiator hose feels hot, the lower radiator hose feels as warm as it should, and warm air blows into the passenger cabin suggesting the heated coolant is circling through the system and into the heater core.
2.The rise in temperature doesn’t activate the radiator fans or I haven't noticed them running.
3.…

Warm, engine operating at 45-50 mph and approx 2100 – 3000 rpm

1.After a couple miles, the heated air from the cabin vents turns cool.
2.After about 5 to 10 miles, a temperature gauge on the dashboard fluctuates up and down but never registers at the engine is overheating. Also, when fluctuating temperature gauge reads higher when throttling, but immediately declines when leading off the gas.
3.…

Warm, engine idling, post-operation and post temp gauge fluctuations:

1.No visible leaks in the lines of the cooling system or radiator.
2.No noticeable or abnormal increases in the line pressure of the cooling system or of one particular hose.
3.There is still a noticeable flow of coolant, passing through the reservoir tank , which is Apparent from removing the cap and looking into the system.

Warm, engine off, post-operation:

1.Coolant is now visible on and around the coolant reservoir tank, suggesting the pressure cap has released coolant from the system.
2.A hissing sound now comes from the cap on the coolant reservoir tank.
3.The level of coolant in the system has decreased.
4.The upper hose, or the line from the engine to the radiator that is connected to the thermostat housing, is now too hot to touch for any longer than a couple seconds if that.
5.The coolant is clearly boiling in the thermostat housing and into about the first quarter of the upper hose.
6.The lower radiator hose is now cool or warm to the touch. Certainly not what you would expect as part of an operational cooling system.
7.The top of the Radiator is hot to touch.
8.The heater core lines, both in and out are also far too cool to the touch. Suggesting there is an inappropriate flow of coolant to the heater core, which is also apparent from the lack of heated air entering the passenger cabin right before the engine shut off.

A few other things to note:

1.If the vehicle is operated before the engine warms up past the first quarter mark of the temperature gauge. The transmission does not shift into the appropriate gear for driving at 55 to 60 mph. It will however shift through the first two or three gears before that mark on the temperature gauge is reached.
1a.I've done a bit of research on issue mentioned above. What I found is a bad coolant temperature sensor can cause or play a significant role in the malfunction I mentioned above.


Thanks in advance for your help. Hope someone out there has a good suggestion and ultimately the solution to the problem What was the condition of the coolant before you serviced the system?

What is the coolant concentration now? What is the ambient outside temperature when this occurs?

Have you had the coolant system pressure checked? Some leaks don't develop unless they are under pressure when the engine is cold.

Have you block tested the coolant system to see if you have combustion gases super-heating the engine coolant?

Did you replace the radiator surge tank cap when you serviced the coolant system?

You can monitor engine coolant temperature with a scan tool that can monitor data stream activity. Thanks for the quick reply!

- I recently had the oil changed at a service station and the coolant condition was just fine or that's what I was told upon its inspection.
- The coolant concentration is now 50/50 give or take a percent or two.
- The ambient outside temperature fluctuates a lot due to my proximity to Lake Michigan and its effect on the weather. It is winter here and its pretty cold most of the time. I'd say somewhere between 5 and 35 degrees F.
- I have not had the coolant system pressure checked. Will be doing that tomorrow morning.
- I have not block tested the coolant system to see if there are combustion gases super-heating the engine coolant. I am unfamiliar with this procedure but will look it up. But if there are combustion gases super-heating the engine coolant would that be visible in the affect coolant's color and quality?
- I have not replaced the surge tank cap at any time. Have order a new one and will replace it.


It sounds like cooling system pressure is critically important. I wonder if that could be the issue? There are no clogs or blockage in the system that I can find or that are apparent. The thermostat seems to be operational and so does the coolant pump. But if the pressure is incorrect could this potentially stop the movement of fluid through the cooling cycle. That seems to be what's happening, the flow is being terminated or drastically reduced during operation when the system needs it most. No flow would explain the boiling coolant coming from the engine at the thermostat. It sounds like pressure testing is the next step. I will look into getting my hands on a scan tool. But in the mean time do you have any suggestions regarding simpler methods of pressure testing? Or could this loss in pressure be responsible for the breakdown of the cooling system? Just wondering; may not have anything to do with your problems but have you flushed the coolant system--radiator. hoses, heater core and all?Car Repair Talk's forum.