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Cooling System Repairs

Air bubbles (by Kestas Smalinskas)

Many Mopar owners have serviced their cooling systems, only to experience problems shortly afterward:

- The engine never reaches full operating temperature, or

- The temperature gauge fluctuates wildly

If the engine doesn't reach full operating temperature, chances are that you replaced the thermostat with one that has an air bleed valve (also known as a jiggle pin, or check valve). This may also set a Code 17 (engine stays cool too long) when you check your onboard diagnostics. The air bleed valve on the thermostat was designed for the 3.0L to allow air out of the cooling system when refilling after service (undoubtedly to avoid the problems discussed in the next paragraph). Unfortunately, it allows too much coolant to circulate through the system and hinders proper warm-up of the engine. This is more noticeable in the cold climates. Get rid of that thermostat. Get one without the air bleed valve.

If your temperature gauge fluctuates wildly after cooling system service, chances are you haven't burped all the air out of the system. Open a high point on the engine side of the cooling system or crack open the thermostat with a screwdriver while filling with coolant (a patented John Auto Tech technique). This should remove the air. The thermostat housing on the 2.2/2.5L engine has a "drain-and-fill" plug at the top for this purpose. If you can remove it - fine. But many have reported problems with the threads seizing. On my cars, I just let it purge itself, topping off the coolant every morning until it stays full.

On 3.0L engines, make sure the thermostat is rotated to the proper position in the housing. The bridge of the thermostat must be aligned with the cast rib (north-south).

Of course, if your thermostat has started to fluctuate wildly, and you haven't recently serviced your cooling system or lost any coolant, then you probably have a bad head gasket which leads us here.

Air redirection

Many people with K-platform cars, built all the way into the 1990s, ("EEKS" - extended K-cars) find that, on hard acceleration, the air will switch from vent or heat to defrost. This is because the system is powered by vacuum (air pressure), and under acceleration, there is less vacuum available. A new and revised part (4677204 - remember that, it's very hard to find in the parts book!), which looks like a 35mm film canister with hose attachments at each end, is available to replace the original tiny triangular piece. It also has better quality attachments to prevent leaks.

On most EEK! cars the check valve is right near the master cylinder and comes out of the brake booster. On some it may be underneath the instrument panel. This is a two minute repair and a $5-$10 part.

Flushing the system

Hank Orsel wrote (slightly edited):

  • The bleeder plug is aluminum in the aluminium head. It [can be] impossible to get out. I had a remanufactured head put on my car, and it was seized. My Dad and I took the thermostat out, and placed a magnet wrapped in a rag in the 'water box' (to catch metal shavings). We then drilled and tapped where the old plug was, and put in an air hose fitting. It was all we had, but turned out to be a great idea. Now I just have to start the car, and push the male end into it. This opens it, and when a little coolant spurts out, I'm done.

    Flushing instructions from the factory service manual, for 1987 front wheel drive vehicles (in my words)

    Drain radiator using valve on bottom-passenger side of car. To change the thermostat: Undo upper rad hose at 'water box' and catch coolant. (100 ml or so) Pull thermostat. Otherwise I wouldn't bother the hose. Coolant capacity for my '87 LeBaron coupe (J) is 9.0 us qt. 8.5 Litres

    You can use a flush kit now if you want.

    Fill radiator half full with 100% coolant. Now the other half with 100% water. Watch the air-bleed hole. Plug the hole when coolant flows from it, then continue. Fill the overflow bottle with 50/50% coolant/water to about a half-inch over the MAX mark (the over-filling is to replace air in the system). Replace all caps and covers.

    Start engine and look for leaks. Let engine run untill it gets hot enough to open the thermostat. Open the air-bleeder once more to examine the level. If there is air, add to radiator until coolant flows. Replace the bleeder plug.

    The radiator should end up about full to the top of the chamber, or to the bottom of the cap. And the overflow bottle between MIN and MAX marks.

    Keep an eye on the level for a couple days afterwards.

Ed Hennessy wrote:

  • In the thermostat housing, there is a purge plug (a threaded pipe plug). Remove that when you drain the radiator, and leave it out as you start filling the radiator, and this will let the air out. When coolant trickles out the hole, put the plug back in.

    Alternatively, fill the radiator, then start the car with the cap off and let the water pump circulate the coolant for 5 or so minutes. Then top the radiator off, and let it circulate. You'll probably have to top it off once or twice more after it circulates.
Ed Treijs wrote:

First of all, the [FWD] Chrysler [heater] cores seem to plug up easily. Do NOT use any stop-leak type products on these cars!

Blowing the core out with compressed air, a number of times, seems to have pretty much unplugged my core. This was from a HD air compressor at a garage, not some cheapo home unit. I've heard of people blowing out heater cores using carwash pressure sprays, but I'd rather not try to empty and refill (and purge!) the heating system in a carwash bay. Plus if your core is weak, I wonder if the pressure spray won't have enough force to blow it out.

If the inlet hose is hot, and the exit hose is cool, and especially if the heat increases when the engine is revved and drops way off at idle, then the core isn't flowing enough. (Steven Thurber noted that these symptoms could also indicate a leaky bypass - Ed agreed).

The system should be full of coolant, and properly purged of air bubbles [Webmaster note: this may also prevent premature head gasket failure].

Next, I don't know about Shadows, but the K-bodies use a funky upper (intake) heater hose. The factory hose has a number of curves molded in. Using a length of regular ol' heater hose pinches the hose no matter how you try to run it. Doesn't help.

If the coolant/water ratio is off too far, like 70% coolant, then the heat transfer is reduced.

As long as the computer doesn't come up with a code 17 (engine runs too cool) your thermostat is likely all right.

Check that the heat door is opening fully. When you whack the temp control lever to full hot, you should hear a thump from under your dashboard as the air-control door hits the stop. If you don't hear this, get underneath the dash and look for the control cable and crank arm assembly. The cable CAN be convinced to shove over a bit.

The specs for heater performance testing, by the way, are:

  • With engine fully warmed and idling, select defrost, max the temp, and put fan on high; heater (foot) outlet air should be a minimum of 144/147F if outside temp is 60/70F (1977 Pontiac service manual said 130 degrees F is "hot).
Ed Treijs wrote about weatherstripping:

My temp control cable feels stiff and the response is rubbery. Moving the lever a little bit results in no change; move it a larger amount and the door kinda jumps to a different setting. Are there any likely *and easy* lubrication points? I don't feel like trying to pull the control head or the heater box, because that looks like a big pain and I'll probably just break something. (1987 Reliant)

  • Steven Thurber noted: The control box is not hard to pull and there is a lube point on that end. Usually the problems are on the other end. Not too hard to pull the whole heater-a/c box per the FSM procedure (I have done it three times on various K-cars) but it is time-consuming if the car has a/c. You could try working the blower speed for a certain amount of fine-tuning.

In a brisk crosswind, there were so many cold drafts inside my Reliant wagon that it was rather unpleasant no matter how much heat the heater put out. The weatherstripping on these cars works okay if it's installed correctly, but after 10 years things go out of whack. Add in that the door hinges go bye-bye, and at least on my car new bushings and pins didn't completely fix the looseness (helped a lot, though).

I took a tube of Permatex weatherstrip adhesive (messy gummy stuff) and went wild.

The big problem is the bottom of the door, where the weatherstrip starts to tilt outwards, or even come loose and droop out the door opening. Anyway, I glued it all down so it sat square, and the curved lip engaged the doorsill.

There were a few gaps along the door sides, especially in the door-to-window frame transition; they were not huge, but got glued anyway.

I "precision adjusted" the doors by moving the door latch post inwards and upwards. They no longer look to line up as if the car was a Mercedes, but there's no more wind noise from the back upper corner at highway speeds.

I took out the rubber flaps which are at the bottom of the doors, at least on K-cars. They aren't part of the door trim, but are installed underneath the trim. I pulled out the bottom of the door trim,
and pulled the rubber flaps off the metal trim clips. The flaps tend to take a set, and after 10 years they're kind of facing outwards at all times, and don't really seal that well against the door sill. What I did was transfer them side-to-side, where they were now facing *inwards*. (Flipping them back to front doesn't work, because the trim clip holes aren't symmetrical front to back.) I had to take extra care in closing the doors the first few times to keep the rubber from jamming at the front edges bending in funny ways; however it didn't take much at all to acclimatize the rubber to its new position.

Final result--a car which should stay a lot warmer (combined with making changes to the heating system like replacing the thermostat). The K-wagons, with extra volume and glass area, are particularly bad for heat. I drive mine with the rear seat down, so as to better hear the speakers and load my mountain bike. This results in cold air from the cargo area sluicing forward between the bucket seats and into my lap. However, with the drafts cut way down, this should not be as annoying as it was last winter.

Avoiding cracked heads

Ron wrote: The correct way to purge the cooling system on the 2.5L is to first remove the threaded plug on top of the thermostat housing, then fill the radiator with coolant until the coolant can be seen in the plug hole, then replace the plug in the housing and finish filling the radiator. If you are losing antifreeze and you can not find any external leaks you may be looking at a bad head gasket. If you end up replacing the gasket make sure to check the head for cracks.

Tom Johnson wrote: I've seen 2.5 engines overheat...when there has been a pocket of air trapped somewhere in the coolong system ( probably in the head). Last time this happened to me I parked the car on a moderate incline, so that the radiator opening was uphill from the engine. I then idled the engine until it warmed up, turned the heater temp control up all the way and toppped off the radiator. The cooling system 'burped' out some air, I topped it off again with coolant, and from then on there was no more overheating.

Heater core leaks

Someone posted that their car overheated due to a stuck thermostat. After the problem was fixed, smoke started to come out of the heater vents, smelling of antifreeze. It slowed down after a few minutes but continued to come out after several days.

Dan Stern wrote that the smoke was probably "Mostly steam with some smoke from where the antifreeze hits the very hot heater fan motor resistor (used to provide different voltages to run the fan at different speeds, and located inside the heater box so the airflow will cool the resistor and prevent it from burning up)."

Edward Hennessy wrote:

What probably happened is that the cloud of steam from overheating got drawn into the cowl vent and into the heating system (much like any outside air would get sucked in and come out the heater vents--ever follow a city bus?).

Assuming your heater core has not sprung a leak (you'd get coolant puddles in the footwells if you did), that's probably all. It has just coated the ductwork, and is working its way out. You'll have to clean the windows really well to get rid of the coating.

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