Hi All,

My vehicle is a:
2008 Dodge Grand Caravan SXT
3.8L V6
145,000 miles

I am experiencing intermittent overheating. Below I'll give a detailed explanation of the symptoms followed by my troubleshooting steps and suspicions. I'm hoping someone can give me some direction on what to do next ...

Details: My caravan started running hotter than normal a couple months ago, it started by going from 1/2 on the temp scale to 3/4 then back down to 1/2 and I didn't think much of it. After a few weeks of this, I suspected that the thermostat was sticking so I replaced it and the symptoms remained. The temp never went above 3/4 so I didn't worry about it much (of course this was during the winter months) however in the past week the temp has spiked to max and the coolent temp light came on, however as I was beginning to pull over the temp quickly dropped back to 1/2 and then stayed under 3/4 for the remainder of the drive. I thought it was peculiar how quickly the temp went from max to 1/2 and I still an unsure what that means.

This past weekend we had to take the van on a longer trip and at highway speeds the van spiked again to max, and I turned on the heater full blast and it brought the temp all the way down to 1/2 where it stayed for the remainder of the drive. So the best I can tell, right now, if I leave the heater on full blast the temp will stay consistantly at 1/2. But, it is getting HOT here in Virginia and this is going to get old quick!

Troubleshooting Steps:

1. Checked Coolant Reservoir --> It is on Max
2. Looked for leaks, no noticable leaks and the Coolant Reservoir is max so I ruled that out.
3. Checked for debris blocking airflow through radiator --> Radiator looks clean
4. Removed thermostat and tested using boiling water --> Stat opened fine before boil (195 degree stat)
5. I left the thermostat out for testing, started the car and was able to get the car's temp back up to 3/4. When doing this I observed that the electric fan cut on as expected. I could also feel the upper coolant hose heat up as the coolant was moving into the radiator.
6. Worth noting, the radiator was replaced about 2 years ago (someone backed into my car), so the rad is fairly new, as is the coolant.

Suspicions:
At this point I'm suspecting the following:

• failing water pump (not moving the coolant through the engine fast enough). Maybe it has been failing over the past couple months which would explain the deterioration in the cars cooling performance (of course the weather warming up could explain that as well)
• Maybe a bad radiator cap (since I don't notice a difference in the radiator reservoir level when the car is hot or cold). Maybe the return valve isn't letting coolant back in the system when the car cools.

So those are my symptoms, troubleshooting and suspicions. I'm getting ready to buy a new water pump and rad cap, but I thought I would post here to see if anyone experienced anything similar.

Are these symptoms consistent with a failing water pump?

Also I have seen some videos on the water pump replacement and it looks pretty doable for a back yard mechanic, thoughts?

Thank you in advance for your time and any help/direction you may be able/willing to provide.

-Mike

 

Have you checked the coolant level in the radiator? The reservoir being at max does NOT guarantee that the radiator is full.

The coolant level in the radiator is the next thing I would check.

 

Although your symptoms aren't consistent with low coolant it's a good idea to check that as suggested above since it's inexpensive. Try replacing the radiator cap too since that's also pretty inexpensive, especially if you know that the cap wasn't replaced with the rad (they aren't always replaced and they don't necessarily have to be).

If neither of those do the trick I would suspect a coolant blockage in the radiator or the hoses to/from it. I say this because you report that the temp goes down to normal with the heater on high. Check that your two rad hoses haven't collapsed, which can result from a bad rad cap. Water pump is also a possibility though usually the pump leaks if it goes bad and that doesn't explain why the temp goes down with the heater on high.

 

kuyabribri & georgef,

Thank you so much for taking the time to reply. I am embarrassed to admit that I had not checked the coolant level in the Radiator. I have always thought the reservoir gave you an indication of the overall fluid level in the system, and never bothered with the Radiator cap since the car was usually hot when I was looking at the cooling system.

So after I saw your posts I went out to the van and opened the Rad cap and couldn't see any fluid. So I ran out to Walmart and got some 50/50 and a new cap, and dumped at least a half-gallon of fluid into my Radiator before it filled up..... ugh! I put on the new cap and started the car. So far so good, I don't see any leaks and the van temp is not going above 1/2. I also noticed this morning that the reservoir level had dropped (which I haven't seen in quite some time), so it looks to be returning coolant back to the system.

Should I worry about how my coolant got so low, or is that to be expected if you have never checked it.

Thanks again for your help!

-Mike

 

Good to hear you're making headway. The rad cap regulates coolant flow to/from the tank so if it was bad it's not surprising that you saw the tank level go down after replacing it. If the cap was bad your missing coolant likely boiled off but you should still keep an eye out for leaks. Place a big piece of cardboard under the car when parking it overnight. You should also keep an eye on the fluid level for the next couple of days as air makes its way out of the system.

 

Will do, thanks again for the quick response. I'll keep you all updated with any changes.

 

FYI to all,

My In-law's 2004 Caravan 3.3L was having similar problems.

I had a look at the rad (full), reservoir (just below Max.), changed the thermostat (which I found out requires a special gasket or it WILL leak), and the problem continued.

Father-In-Law tells me the Check Engine lights been on for three months. I check the code and it tells me something's up with the cooling system.

So I checked the two rad fans manually, and one of them was seized up tight. I couldn't even turn it by hand after it was removed.

This caused the main 40A fuse to blow.

I replaced the fan and the fuse, and they've had no problems ever since.

 

Something I come across quite often believe it or not are water pumps with the blades eaten off of them by improper mixing of coolant or non-HOAT coolant(maybe not non-HOAT but if you aren't using it with these you're an idiot). Also it's insanely easy to warp heads on all generations of C/GC and voyager and probably block surface too even though I haven't had one yet..

All vans with eaten away pump blades will over-heat one-mile down the road, sometimes only if you run AC.

I'd say pretty much all mechanics are just going to throw generic non-HOAT coolant in your van too because they are such legendary experts who if they even know why it should be used make the assumption you'll flush your system routinely and not notice leaks for about 60k where they will profit from the head replacement... This is why I do my own flushes and use Zerex G-05 and save insane amounts of money from logic-bomb mechanic work..

 

Old timers start out with a cold engine, then run the van in park with the radiator cap removed, let everything heat up until the thermostat is open, let the air burp out, stop the engine and fill the radiator to correct level, put the cap back on. I think that will still work for modern engines, but of course, be super careful not to scald yourself.

 

If I have a hose I take the thermostat out and flush the block and radiator on everything I own. I put in a new thermostat every 60k or before long trips since they are pretty cheap new.

The only thing that works with aluminum engines is paranoia and not letting mechanics just put anything in your radiator..

The one good thing with these is that they are push rod engines, so doing head work is pretty easy relativity speaking..