2000 Grand Caravan 3.3 Overheating

My GC is overheating. Started as occassionally but now increasing in frequency. I find it will being to overheat after driving on the interstate for half hour or so but I can "calm" it back down but turning on the heat.
I've replaced the following:
1. coolant (no drips or leaks nor am I losing coolant over time)
2. thermostat (twice)
3. temperature sensor
4. serpentine belt and tensioner
5. radiator (last summer)
6. water pump (last winter)

I notice the fans run more often than they should. For example, after a 10 minute ride to work in the morning,. I notice the fans are running as I pull into my parking space.

rw, how about the radiator cap? when started cold how long does it take to overheat? Checked airflow through radiator, making sure nothing is blocking airflow?

I forgot to mention that I had also replaced the radiator cap just recently. There doesn't appear to be any airflow restriction.

rw1644h, the only other thing I can think of at the moment, have you did a backflush of the cooling system? Any other problems with the van like check engine light on?

No CEL's. I connected a scan tool; no faults. Regarding backflush, with the recent work I've done, I've did a prestone flush solution and drained. Also, after that, I've drained the coolant a few times to perform other work. Once by disconnecting hose at water pump. It drained like a torrent. I never power flushed though, if that's what you mean...

rw, kind of unlikely but it does happen is that deposits or sediment settles in the waterjacket of the block and slows or stops coolant circulation, sometimes you have to buy a kit from the parts house and splice it into the heater hose to flush out the block. You have just about covered everything else, does the engine seem to run as good as it always has?

Are you sure its not the gauge or sending unit?

If the sensor is what you're referring to, I just replaced it. Correct me if I'm wrong but isn't there only one coolant temp sensor? I don't see a second sensor/temp switch listed on the major parts suppliers' websites. The gauge needle is moving in an reasonable fashion but I can't say whether the gauge is mis-indicating.

One coolant temp sensor and probably an engine temp sensor to run the gauge. I'm at a loss, you have covered most everything and the fans seem to be working. Try checking the actual engine temp with an infrared thermometer. Good luck

There's one single ECT sensor for the combined gauge and PCM signals. Ask a rad shop what they use as a flush solvent. Did this problem start before all the parts were changed?

My GC is overheating. Started as occassionally but now increasing in frequency. I find it will being to overheat after driving on the interstate for half hour or so but I can "calm" it back down but turning on the heat.
I've replaced the following:
1. coolant (no drips or leaks nor am I losing coolant over time)
2. thermostat (twice)
3. temperature sensor
4. serpentine belt and tensioner
5. radiator (last summer)
6. water pump (last winter)

I notice the fans run more often than they should. For example, after a 10 minute ride to work in the morning,. I notice the fans are running as I pull into my parking space.
Check the oil for radiator coolant. to check this all you need to do is pull out the oil dipstick and look for a "milky" film. Kind of looks like Bailey's Irish Cream. That will tell if you have a bad head gasket. There is another way to tell if it is, what you call a radiator check valve, the thermostat. When the car is cool remove the radiator cap, grab the top radiator hose leading to the thermostat housing, and gently squeeze the top radiator hose. If you see air bubbles in the radiator, the thermostat needs to be changed.
I understand you installed the thermostat twice and water pump. I'm going with bad head gasket...Good luck!

The oil is nice and black, not creamy.

I can drive all day with the heater on high.

I did another CO2-in-the-coolant check with a borrowed "Blue Point combustion Leak tester"; came up negative.

I'm wondering if I have coolant flow blockage to the radiator.

The only problem is a schematic. Searches turned up negative. Even the on-line parts suppliers (even the Mopar ones) don't list all the components. Yeah, the standard stuff is there: radiator, WP, T-stat, etc, but nothing on the bypass and heater hose side of things. So, that being said, I'll start by asking questions.

From the water pump, a hose travels along the front bank. and then where...

From the driver side of the block, a flanged pipe turns ninety degrees and towards the firewall.

Question: With the heater NOT on high, starting at the WP, what is coolant flow path?

Check the belt and tensioner again. It may be slipping at hiway speeds. If I remember that tensioner has a built in indicator on the casting to show if theres enough tension being applied to the belt. The belt might have oil or dirt on it or be a 1/2 inch too long also the radiator might not have enough flow.

Belt tensioner/belt are fine. I replaced them both 3 weeks ago and the same behavior. I would think if its a lack of flow due to slippage, then "heater-on-high" would not relieve the problem.

Does it get hot enough to throw the "check guages" light and chime? Or does it just read hotter than normal?

If if just reads hotter than normal, I'm wondering what kind of radiator they sold you. Does it have one row of vanes or two? Cheaper after-market radiators sometimes have less cooling capacity than originals which cause the vehicle to run warmer. Although, they SHOULD keep the car sufficiently cool.

Another possible problem could be some trapped air.

Good luck.

rw, I'll have to check the hose routing and get back to you but yes maybe you do have a blockage somewhere in the system and when you have the heater on high that creates a little more capacity in the system.

The gauge climbs above normal. It then keeps going to 60%, 70%, 80% then I get nervous and throw on the heat full blast and it comes back down. This behavior is repeatable.


I've been reading on other forums on heavy duty flushes. Suggestions abound, of course. Gunk 2232 and GM P/N 12346500 are common commercial suggestions and, of course, home-made concoctions like cacscade dishwasher detergent.

I think I'll go to a radiator shop and see if they can hook me up with some thing they've used....

Well, I decided to go cheap and simply used some non-sudsing dishwasher powder. Ran it for a few hours, drained, and thoroughly flushed. Result: still overheating.

Before jumping into the head/headgasket job, I wanted to be absolutely sure it was not the cooling system. So, I removed the radiator and took it to a rad shop. They checked flow and immediately noticed the problem: a failure of the baffle that diverts flow through the radiator. The guy told me there was no flow through the radiator; the water flowing in was immediately flowing out. Back to parts store. As the radiator was less than a year old, they just gave me a new one.

Yippy !!!!

rw, way to go!

I want to thank rw1644h for updating his post. I had the exact same problem and was ready to do a head job when I read his post. I installed a new radiator and problem is solved. I had put on all the same things and the old radiator was replaced 35,000 mile ago. So it pays to read these post. Again thanks much rw1644h.