94 Dodge Caravan won't stop running hot

[huntersdada]

Busted the main hose last week, serpentine belt slipped off somehow (I guess from all the anti-freeze).

Replaced the belt and hose, filled with about a 70/40% mix of AF/water.

Doing fine, but still running hot when idling for more than a few minutes.

Any ideas?


Edited to add...3.3 ltr V-6

 

[The Mountain]

Thermostat busted? Water pump not pumping? Temp sensor for the fan not working? Coolant system need to be flushed? Radiator clogged with insect carcasses? Check these in reverse order (bug problem is easiest, thermostat most involved).


If the radiator is dirty, go to a do-it-yourself wash bay and use the high pressure sprayer on it. Open the hood and spray into the rad from the back (going from the front only pushes the gunk further into the cooling fins).

If that isn't it, go somewhere where you can get the cooling system flushed (preferably power-flushed). That should clean out any sediment that has built up in both the rad and the engine block. This is actually a pretty simple procedure, but it is messy, and has a high potential for dumping coolant all over the ground. Shops have equipment to catch any and all coolant, and can send it off to be recycled. Yes, you will have to buy more coolant, but then, an engine is so much more expensive (and dodge minivan engines aren't exactly paragons of durability).

Your local library should have a repair manual you can use to look up how to check the sensor for the electric cooling fan (or sneak the wrapper off the appropriate manual at Barnes and Noble ). The sensor itself should be pretty cheap. Alternatively, if you have a mechanical fan (engine-turned), get the motor good and hot, then shut it off and see if the mechanical clutch on the fan is engaged. If you can turn the fan relatively easily, then you need a new fan clutch.

Next, wait for the radiator to cool a bit, until you can comfortably touch the radiator cap, then open the radiator and start the engine. See if the coolant is flowing adequately. If not, your pump is fragged or the thermostat is stuck closed. Unless you are mechanically inclined, that is a job for your local mechanic.


If you do take on either of the last two jobs yourself, use a repair manual. With so much aluminum on today's engines, all it takes is one overtorqued bolt to strip an important thread and ruin your day, and maybe the engine block. Have Heli-Coils handy just in case, and know how to use them.

 

[huntersdada]

Thanks LP...I will try that advice.

Sounds simple enough.

 

[The Mountain]

edited the above for clarity w/regard to different types of cooling fans.

 

[OddOne]

One that's VERY often overlooked, even by professional mechanics:


Check for a bubble or pocket of air in the cooling system.


Strange as it may sound, it's very easy for an air pocket to impede the flow of coolant enough to cause overheating, and it will NOT go away until the air is bled from the system.


Here's how to check for an eliminate air from cooling systems:

1. Start with a cold engine. Take off the radiator cap and top off the coolant in both radiator and overflow tank with coolant or DISTILLED water. Turn ON the heater and set the fan speed to the lowest setting.
2. Start the engine and let it warm to operating temp at idle. Watch the temp gauge at all times, as an air pocket can cause a sudden sharp temp increase! (NOTE: If you don't have a temp GAUGE, it is wise to let a technician monitor the coolant temp with a scan tool. DO NOT RELY ON IDIOT LIGHTS!) If the temp starts to jump rapidly, or gets over 230 deg. F, shut the vehicle down and troubleshoot for cooling system problems (stuck thermostat, failing water pump, etc.)
3. Periodically check the coolant level in the radiator, topping off if necessary. (Some will probably spill out, which is normal for this procedure.)
4. Once the temp reaches the thermostat's opening temp (usually 198 to 220 degrees, depending on the vehicle), top off the radiator again. (You'll know when the thermostat opens, as the radiator's coolant level will suddenly drop, as will the coolant temperature.)
5. The cooling fan should come on once the coolant temp restabilizes, which usually will be 3-5 thermostat open/close cycles. If it does not, shut the vehicle down and troubleshoot the cooling fan.
6. Continue the process until the cooling fan has cycled on and back off AT LEAST THREE TIMES. If watching the temp with a gauge or scan tool, it should become possible to estimate where the fan will come on and shut off.
7. Top off the radiator as necessary and put the cap back on.


Failing to get all the air out of the cooling system is one of the more common points of failure for cooling systems, and one of the most common causes of a vehicle running hot.

oO

 

[The Mountain]

As a follow-up to oddOne's note, don't use distilled water. Distilled water was ok when the engine was iron and the radiator was brass, but now that both are primarily aluminum, yet still have iron present, distilled water actually makes things worse. It magnifies the chemical differences in the metals, causing the water jacket to corrode (turns the system into a giant, weak chemical battery. And yes, I cannot remember the specific term for this). For new(er) engines, use de-ionized water, which you should be able to get at an autozone or similar. You can also use tap water, which will still cause some of the battery effect, and increases the potential for scale to form, but still better than distilled.


Apart from that, he makes a good point, especially since you lost a coolant hose, which is a real easy way to introduce air into the system inside the engine block.

 

[WFK]

If you took the fan blade off did you put it back on correctly? Front/back? (Had an A/C tech do that to me once)

 

[huntersdada]

WFK, I never took the fan blade off...didn't have to...I hope.

 

[rryan]

Oddone is right about air---AND if the radiator is lower than the highest point of cooling in the heads, an air pocket there WILL warp the heads---you can get the system evacuated, or (always worked for me) jack the front of the car WAY up, take the cap off and run it for aminute--shoulld allow the air out.

 

[Turnpike Jim]

Couple of questions
when it first overheated, did you shut it down right away?
How many miles on the engine?

If you ran it overheated for any legnth of time, you probably have warped at least one head and blown the head gasket. If thats the case, have both heads pulled of. If you don't have a lot of miles, you may get away with having them resurfaced. (about $50.00 each for degreasing and resurfacing)

Lot of miles and/or severly overheated? Spend the money to have a valve job/ resurface done. This will insure that the heads are not cracked. Also, those heads tend to drop quides when they get hot (excessive oil consumption/possible valve not closing) This could run several hundred dollars, but lots cheaper than a new car.

Aluminum heads warp if you look at them funny. Hope the problem is one of the easy ones listed in previous posts.

Good luck
Jim

 

[Blu3duk]

another reason for over heating in some of the older dodges can be the smog filter inside of the exhast..... it gets full of carbon, and then nothing can stop it from overheating..... next stop blown head gasket..... which increases the over heating problem..... $2500.00 later you have a new engine...... and a $500.00 car but that is only from experience.

The way to check if that is the problem is to let it get hot.... and open the hood at night, the exhaust glowing red will be a good indication that this may be your problem. Hopefully it is not.