jthiesen1169

Here's my dilemma.

One year ago at about 85K miles, my 2000 started to overheat. It came on suddenly. One day it was running fine, next day the temps skyrocketed into the red, even while driving on the freeway. I replaced the thermostat but likely did not purge (burp) the system properly and was still having the same exact issue. So, I replaced the water pump with a Bosch pump. I refilled and burped the system as instructed and bam, no more overheating issues. The car ran perfect as before. When the temp would hit 230, the fans would hit high and drop in back down to 220. While driving, it rarely would go over 200. I realize that if I had burped the system when I replaced the thermostat, it would have likely been fine and not needed the water pump. Lesson learned. The water pump was not leaking or making noise. When I took it off, it spun just fine and the impeller didn't appear to be clogged. I replaced it anyway.

Now, again, at 101K miles, the car is all of a sudden overheating. Only this time, it will stay cool while driving, but then overheat in traffic. Once the temp hits 220, it skyrockets up past 240 and both fans turn on high but the temp will continue to slowly creep up to the red. I took the radiator cover off and there was a good amount of debris. I bought a long BBQ grill brush that would fit down in between the condenser and the radiator and brushed all that crap out of there and off the front of the condenser. I still had the same problem. Then I replaced the thermostat and burped the system. I still have the same problem.

If it's debris still stuck in the radiator fins, wouldn't I see temps gradually increasing over time instead of all of a sudden? Also, the water pump is only a year old. Now, this doesn't mean it can't fail, but I'm thinking that the radiator is possibly clogged inside and/or the fins are probably still full of junk that the brush didn't get out. Both hoses are hot with the one near the thermostat being hotter as it should. The fact that it runs at normal temps while driving leads me to believe it's not the pump.

I don't want to spend money I don't have to. From what I've described, what do you think it is? Radiator problem or the water pump again? Is there any way to clean out the radiator without pulling it? The fans appear to be turning on at the correct temps. I did the water pump myself and it was a bitch to get the gaskets lined up and a couple of the bolts back in, but an hour or so and many curse words, I got it all together. I used the opportunity to replace all of the idler pulleys as they were easily accessible with the water pump off.

Your input and experience is appreciated. She'll have to sit in the driveway until I can figure it out.

73Corvette

I know this is a long read, but it will help you understand all the in's and out's, do's and don'ts ... how's and why's
IMHO you need to take the radiator out to clean it... I was convinced mine was pretty dang clean till I took it out... I couldn't even see through the fins it was so packed with a dust/muddy/dried/ mortar type crap that I had to soak with the hose and then gently blow out with a garden hose nozzle...about 10 times before I finally got it clean, then you could see right through it.



Cooling System Description and Operation

Cooling Fan Control

The engine cooling fan system consists of two electrical cooling fans and three fan relays. The relays are arranged in a series/parallel configuration that allows the powertrain control module (PCM) to operate both fans together at low or high speeds. The cooling fans and fan relays receive battery positive voltage and ignition 1 voltage from the underhood electrical center. The ground path is provided at G102.

During low speed operation, the PCM supplies the ground path for the low speed fan relay through the low speed cooling fan relay control circuit. This energizes the cooling fan 1 relay coil, closes the relay contacts, and supplies battery positive voltage through the cooling fan motor supply voltage circuit to the left cooling fan. The ground path for the left cooling fan is through the cooling fan 3 relay and the right cooling fan. The result is a series circuit with both fans running at low speed.

During high speed operation the PCM supplies the ground path for the cooling fan 1 relay through the low speed cooling fan relay control circuit. After a 3-second delay, the PCM supplies a ground path for the cooling fan 2 relay and the cooling fan 3 relay through the high speed cooling fan relay control circuit. This energizes the cooling fan 3 relay coil, closes the relay contacts, and provides a ground path for the left cooling fan. At the same time the cooling fan 2 relay coil is energized closing the relay contacts and provides battery positive voltage on the cooling fan motor supply voltage circuit to the right cooling fan. During high speed fan operation, both engine cooling fans have there own ground path. The result is a parallel circuit with both fans running at high speed.

The low speed cooling fan is commanded on when the coolant temperature reaches 108°C (226°F). It is turned off if the coolant temperature lowers to 104°C (219°F). The high speed cooling fan is commanded on when the coolant temperature reaches 113°C (235°F). It is turned off if the coolant temperature lowers to 108°C (226°F). When the A/C is on and the coolant temperature reaches 85°C (185°F), the low speed cooling fan will be turned on at vehicle speeds less than 56 kPh (35 mph).



Engine Coolant Indicator(s)

COOLANT OVER TEMP

The IPC illuminates the COOLANT OVER TEMP indicator in the message center when the following occurs:

The PCM detects that the engine coolant temperature exceeds 124°C (256°F). The IPC receives a class 2 message from the PCM indicating the high coolant temperature.
The IPC will also illuminate the CHECK GAGES indicator and a chime sounds when this condition exists.
Cooling System
The cooling system's function is to maintain an efficient engine operating temperature during all engine speeds and operating conditions. The cooling system is designed to remove approximately one-third of the heat produced by the burning of the air-fuel mixture. When the engine is cold, the system cools slowly or not at all. This allows the engine to warm quickly.



Cooling Cycle

Coolant is drawn from the radiator outlet and into the water pump inlet by the water pump. Some coolant will then be pumped from the water pump, to the heater core, then back to the water pump. This provides the passenger compartment with heat and defrost.

Coolant is also pumped through the water pump outlet and into the engine block. In the engine block, the coolant circulates through the water jackets surrounding the cylinders where it absorbs heat.

The coolant is then forced through the cylinder head gasket openings and into the cylinder heads. In the cylinder heads, the coolant flows through the water jackets surrounding the combustion chambers and valve seats, where it absorbs additional heat.

Coolant is also directed to the throttle body. There it circulates through passages in the casting. During initial start up, the coolant assists in warming the throttle body. During normal operating temperatures, the coolant assists in keeping the throttle body cool.

From the cylinder heads, the coolant is then forced to the thermostat. The flow of coolant will either be stopped at the thermostat until the engine is warmed, or it will flow through the thermostat and into the radiator where it is cooled and the coolant cycle is completed.

Operation of the cooling system requires proper functioning of all cooling system components. The cooling system consists of the following components:



Coolant

The engine coolant is a solution made up of a 50-50 mixture of DEX-COOL and clean drinkable water. The coolant solution carries excess heat away from the engine to the radiator, where the heat is dissipated to the atmosphere.



Radiator

The radiator is a heat exchanger. It consists of a core and two tanks. The aluminum core is a crossflow tube and fin design. This is a series of tubes that extend side to side from the inlet tank to the outlet tank. Fins are placed around the outside of the tubes to improve heat transfer from the coolant to the atmosphere. The inlet and outlet tanks are molded with a high temperature, nylon reinforced plastic. A high temperature rubber gasket seals the tank flange edge. The tanks are clamped to the core with clinch tabs. The tabs are part of the aluminum header at each end of the core. The radiator also has a drain **** which is located in the bottom of the left hand tank. The drain **** includes the drain **** and drain **** seal.

The radiator removes heat from the coolant passing through it. The fins on the core absorb heat from the coolant passing through the tubes. As air passes between the fins, it absorbs heat and cools the coolant.

During vehicle use, the coolant heats and expands. The coolant that is displaced by this expansion flows into the surge tank. As the coolant circulates, air is allowed to exit. This is an advantage to the cooling system. Coolant without bubbles absorbs heat much better than coolant with bubbles.



Pressure Cap

The pressure cap is a cap that seals and pressurizes the cooling system. It contains a blow off or pressure valve and a vacuum or atmospheric valve. The pressure valve is held against its seat by a spring of predetermined strength, which protects the radiator by relieving pressure if it exceeds 15 psi. The vacuum valve is held against its seat by a spring, which permits opening of the valve to relieve vacuum created in the cooling system as it cools off. The vacuum, if not relieved, might cause the radiator to collapse.

The pressure cap allows pressure in the cooling system to build up. As the pressure builds, the boiling point of the coolant goes up as well. Therefore, the coolant can be safely run at a temperature much higher than the boiling point of the coolant at atmospheric pressure. The hotter the coolant is, the faster the heat moves from the radiator to the cooler, passing air. The pressure in the cooling system can get too high, however. When the pressure exceeds the strength of the spring, it raises the pressure valve so that the excess pressure can escape. As the engine cools down, the temperature of the coolant drops and a vacuum is created in the cooling system. This vacuum causes the vacuum valve to open, allowing outside air into the cooling system. This equalizes the pressure in the cooling system with atmospheric pressure, preventing the radiator from collapsing.



Surge Tank

The surge tank is a plastic tank with a pressure cap mounted to it. The tank is mounted at a point higher than all other coolant passages. The surge tank provides an air space in the cooling system. The air space allows the coolant to expand and contract. The surge tank also provides a coolant fill point and a central air bleed location.

During vehicle use, the coolant heats and expands. The coolant that is displaced by this expansion flows into the surge tank. As the coolant circulates, air is allowed to exit. This is an advantage to the cooling system. Coolant without bubbles absorbs heat much better than coolant with bubbles.



Air Baffles and Seals

The cooling system uses deflectors, air baffles and air seals to increase system cooling. Deflectors are installed under the vehicle to redirect airflow beneath the vehicle to flow through the radiator and increase cooling. Air baffles are also used to direct airflow into the radiator and increase cooling. Air seals prevent air from bypassing the radiator and A/C condenser. Air seals also prevent recirculation of the air for better hot weather cooling and A/C condenser performance.



Water Pump

The water pump is a centrifugal vane impeller type pump. The pump consists of a housing with coolant inlet and outlet passages and an impeller. The impeller is a flat plate mounted on the pump shaft with a series of flat or curved blades or vanes. When the impeller rotates, the coolant between the vanes is thrown outward by centrifugal force. The impeller shaft is supported by one or more sealed bearings. These sealed bearings never need to be lubricated. With a sealed bearing, grease cannot leak out, and dirt and water cannot get in.

The purpose of the water pump is to circulate coolant throughout the cooling system. The water pump is driven by the crankshaft via the drive belt.



Thermostat

The thermostat is a coolant flow control component. It's purpose is to regulate the operating temperature of the engine. It utilizes a temperature sensitive wax-pellet element. The element connects to a valve through a piston. When the element is heated, it expands and exerts pressure against a rubber diaphragm. This pressure forces the valve to open. As the element is cooled, it contracts. This contraction allows a spring to push the valve closed.

When the coolant temperature is below 91°C (195°F), the thermostat valve remains closed. This prevents circulation of the coolant to the radiator and allows the engine to warm up quickly. After the coolant temperature reaches 91°C (195°F), the thermostat valve will open. The coolant is then allowed to circulate through the thermostat to the radiator where the engine heat is dissipated to the atmosphere. The thermostat also provides a restriction in the cooling system, even after it has opened. This restriction creates a pressure difference which prevents cavitation at the water pump and forces coolant to circulate through the engine block.



Transmission Oil Cooler

The transmission oil cooler is a heat exchanger. It is located inside the right side end tank of the radiator. The transmission fluid temperature is regulated by the temperature of the engine coolant that surrounds the oil cooler as the transmission fluid passes down through the cooler.

The transmission oil pump, pumps the fluid through the transmission oil cooler feed line to the oil cooler. The fluid then flows down through the cooler while the engine coolant absorbs heat from the fluid. The fluid is then pumped through the transmission oil cooler return line, to the transmission.



Coolant Heater

The optional engine coolant heater (RPO K05) is rated at 400 watts and supplies 1365 btu/hr. The engine coolant heater operates using 110-volt AC external power and is designed to warm the coolant in the engine block area for improved starting in very cold weather -29°C (-20°F). The coolant heater helps reduce fuel consumption when a cold engine is warming up. The unit is equipped with a detachable AC power cord. A weather shield on the cord is provided to protect the plug when not in use.

jthiesen1169

Ok, so upon further investigation with the car up in the air, there is no coolant running through the radiator at all. The radiator is cold, even when the car heats up to 235F.

I've tried burping the system several times. When I did it when I replaced the water pump, it wasn't that difficult. I just replaced the thermostat but that doesn't mean I couldn't have gotten a bad one out of the box. I'm going to run it without a thermostat and see if that solves it. If not, it appears it's water pump time AGAIN! I just put a new pump in it a year and four months ago.

Has anyone had bad experiences with Bosch pumps? I thought Bosch was a good quality line. It was new and not a rebuild.

Any recommendations for a good quality pump?

73Corvette

https://www.corvetteforum.com/forums...waterpump.html

I hope it's the thermostat...

2FAS4UU

I can see that this has driven you nuts, but as for a solution, I can only offer my advise and experience with the intermittent overheating issue. I had done what many have tried before, fabricated water nozzle wands, air nozzle's, etc. The one solution that worked for me was to pull the radiator 'Out' !! I soaked the radiator down with 'Simple Green' and let it sit for awhile (20-30 min.). I then began the tedious task of taking the bristles of a toothbrush and started pushing them through the vanes(both sides),Whew !! I was blown away by the amount of debris removed, approximately 2 1/2 cups of mostly silty sand fiberous material. It's the only way to know for sure that you have a 'Clean' radiator on the exterior. I then sent it out to a shop and had a flush/pressure check done on it, re-installed it and 'Bam', good to go. And you also need to attack the A/C vanes as well, although it cleaned better with less debris removed. Good luck and take your time, it's worth it !!

P.S. I know this doesn't address the water flow issue, but it's part of the process of a efficient cooling system!! Stat, water pump and/or possible old hoses collapsed.

73Corvette

You are ABSOLUTELY, POSITIVELY, CERTIFIABLY.. correct. There would be quite a few less overheating threads if everyone would do this. I thought mine was perfectly fine after removing the top shroud and just inspecting with a light between the condenser and the radiator...boy, was I wrong, like you mine was packed with crap that wouldn't "blow out" with air and took a lot of soaking and rinsing to get it clean, after I took it out.

2FAS4UU

Thanks for your reply 73Corvette !! I know a lot of people are hesitant or dread to go through this process, but it's one day of work that pays off for the remaining 364 days and years of confident driving to come. It also makes for a good opportunity to detail !! Jus Say'n !!

jthiesen1169

Ok guys,

I'm going to take the radiator out and clean it for sure, but my problem is that I have ZERO flow through the radiator. The radiator is cold the entire time the car heats up until it gets to the red. I also have no flow through the heater core. Turned the heat all the way up, blows outside air temp only.

Here's what I've done so far to try and figure it out and I have tried to burp the system with every attempt:

1. Replace thermostat - Still no flow
2. Remove thermostat out of old spout for straight flow - Still no flow
3. Replace water pump - Still no flow

My only other option is to remove the radiator and have it cleaned out internally. I don't understand how a radiator can just, all of a sudden, completely clog internally. One day the car was running normal temp wise, the next it begins to overheat. It did come on gradually, but all in one day. From rising temps while driving to now just going to the red.

I am at a loss. I just burned $235 and got nowhere. The water pump I put on it previously probably had less than 20K miles on it.

2FAS4UU

JThiesen, you are at that point that makes or breaks. I will tell you that the cleaning process is just good sense to do so you can rule out the clogged exterior vanes on the radiator/A/C core issue. Check your old hoses to make sure that they are not collapsing at running temperatures (do this before taking out the rad). I am having a hard time believing that the inside of the rad is completely clogged, but stranger things have happened, which makes me go back to the hose issue. Installing a 'used' water pump creates questions about no water flow as well, (bad impeller,maybe). Good luck and let us know how and what you found out.

73Corvette

Ok this just doesn't make any sense. If your thermostat is OUT it almost has to be the water pump...there isn't anything else to keep the fluid from circulating...unless 8vtte7 is right.

jthiesen1169

I've only used Dex cool and the color is fine, no mud. I flushed the system about two years ago, then replaced the water pump with a new Bosch pump and thermostat just over a year ago and topped off with more Dex cool.

After reading other threads with guys having the same dilemma, I loosened the plates at each head for the little crossover pipe and some air came out of the right head but not much. Then, once the coolant began to boil internally, only steam would come out and it was like the water pump was pumping air, pushing the steam out faster.

It keeps sucking up coolant. I'll top off the surge tank when it's hot, then once the car cools off, all the coolant from the tank is gone. I've done this about three times now. I didn't get to work on it yesterday, but will give it another shot today. I think I'm going to pull the top radiator hose and pour coolant in it till it stops. This will hopefully fill the pump, heads, and block and maybe get this air pocket out.

Super frustrating. I don't know what even caused the overheating in the first place and now it just pegs out no matter what due to no coolant flowing. When symptoms first started, the car would reach about 240-245F in traffic and both fans would be on high but it was drive-able. Temp would come down under 220F driving above 40mph. Could have been clogged fins causing that or a bad thermostat again.

All I can do is keep troubleshooting and pray it's an easy and inexpensive fix at this point.

I really appreciate all the responses!

runner140*

I'm thinking water pump too.
With the pressure cap off and the motor running, you should see the flow when warmed up.....or an air bubble and needs a super bleed.

jthiesen1169

Took thermostat out with old pump still in place - no flow.

Replaced water pump with new pump, re filled with coolant - no flow.

It has to be an air pocket and the pump is not picking up the coolant. I'm just going to have to fight it until it finally takes the coolant and purges the air out. I love this car, but it can be a BIG pain in the *** sometimes.

2FAS4UU

I feel your pain, but persistence will pay off !! Your situation is a bit bizarre although fixable, does it make you feel like a detective trying to solve a murder !! Just kidding, I really am curious about your situation and hope you find a resolve to it soon. Please post what the problem was after the fix !!

jthiesen1169

If that were the case, wouldn't I feel pressure in the hose coming out of the water pump to the radiator? I feel nothing, no flow, and the only reason the hose is hot is from heat radiating off the pump nozzle. When I pinch the hose shut, there's nothing, no pressure or coolant in there at all.

73Corvette

Looks to me like it would simplest to just remove the radiator, it's a simple task.... your going to clean it anyway, then while you have it out you can put a hose in the upper outlet and see if the water will come out the bottom outlet to check for blockage...

73Corvette

Would the pump "sucking" on the blocked radiator cause the lower hose to collapse?

Lee DeRaud

The heater hoses connect directly to the pump, so that rules out the radiator and thermostat, right?

jthiesen1169

Just how easy is it to take the radiator out? It looks like a pain in the ***. I'm assuming it slides out the top? Is it bolted to the fan shrouds anywhere?

My drain valve on the radiator is busted. It doesn't leak, but I cant' open it now. When I did a flush a couple years ago, there wasn't any sludge or particles present.

Lee DeRaud

So open the big "drain valve": disconnect the lower hose.