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Discussion Starter #1
I have a 2001 Intrepid, 3.2. Last year I had the following replaced on the car:

Upper and lower radiator hoses
Radiator (filled with HOAT 50/50 coolant)
Thermostat (Mopar) - not installed backwards
Heater tube
Upper intake gasket
Serpentine belt
Both cam seals because of oil leak
Water pump not replaced because fairly new, however, the pump o-rings were replaced due to coolant leak
Switched the upper intake from my 3.2 Concorde because the one from the trep in better condition.

After work completed car overheats, but needle moves below halfway when turn on heater. Each time overheated, the system bled until no bubbles.

No loss of coolant and no milky color of inside of oil filler cap, therefore, head gasket likely not blown. Heater blows hot, so likely not caused by a bad heater core.

No air bubbles in coolant at the bleeder port, today. Coolant level in reservoir is consistent. Today, overheated after a 5 minute drive 40 F degrees outside. Upper radiator hose warm, and radiator cold too.

Any ideas as to cause of engine overheating?
 

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Water Pump. Possible impeller slipping on shaft.

What brand water pump and what part number?
 
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If you have a cylinder leak to the cooling system, you won't get oily residue in the coolant. There are tests designed to detect a cylinder leak. I've been out of circulation for a while, but these tests use coolant additives to detect the presence of compression gasses. I'm sure they've improved since I last used them years ago.

Add to the case a cylinder leakdown test when engine is warm. That's my bet.
 

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Discussion Starter #5
Water Pump. Possible impeller slipping on shaft.

What brand water pump and what part number?
After discussing with mechanic, it could be a Gates water pump because the timing belt is a Gates and they are usually purchased as a kit, and both looked in excellent condition.
 

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Discussion Starter #6
If you have a cylinder leak to the cooling system, you won't get oily residue in the coolant. There are tests designed to detect a cylinder leak. I've been out of circulation for a while, but these tests use coolant additives to detect the presence of compression gasses. I'm sure they've improved since I last used them years ago.

Add to the case a cylinder leakdown test when engine is warm. That's my bet.
The coolant level was unchanged after arriving home so it's a low probability it's a cylinder or head gasket leak.
 

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Good suggestions.

I'm thinking add to the possibilities that thermostat is sticking closed (was it tested in pan of water on stovetop before installed?).

(Keep in mind that the heater core loop is open all the time (meaning no coolant flow restriction, i. e., no valve in the coolant loop) - heat output to cabin controlled by cabin air being directed thru (heat "on") or diverted around (heat "off") heater core.)

To rule in/out impeller slipping on shaft, idle cold engine, then while squeezing upper rad. hose slightly shut with hand, speed engine up. If definitely feel upper rad. hose expand due to increased pressure from water pump when rev'ing engine, impeller probably not loose on shaft. If not much or no change in pressure felt in upper rad. hose when rev'ing engine, impeller may be loose or missing (exploded).
 

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Am I properly remembering that these 3.2L and 3.5L engines were upflow systems? If the radiator is cold and the upper hose is warm or hot, (Trying to remember the last comment in the OP), then I suggest a restriction either in the radiator, or that properly installed t-stat.

Saw this on another site. Hopefully, it won't be this involved...

 

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Discussion Starter #9
Good suggestions.

I'm thinking add to the possibilities that thermostat is sticking closed (was it tested in pan of water on stovetop before installed?).

(Keep in mind that the heater core loop is open all the time (meaning no coolant flow restriction, i. e., no valve in the coolant loop) - heat output to cabin controlled by cabin air being directed thru (heat "on") or diverted around (heat "off") heater core.)

To rule in/out impeller slipping on shaft, idle cold engine, then while squeezing upper rad. hose slightly shut with hand, speed engine up. If definitely feel upper rad. hose expand due to increased pressure from water pump when rev'ing engine, impeller probably not loose on shaft. If not much or no change in pressure felt in upper rad. hose when rev'ing engine, impeller may be loose or missing (exploded).
The thermostat was replaced twice last year...1st with a Carquest brand, and when car continued to overheat, it was replaced after car driven only a few times with a Mopar that I purchased from the Dodge dealer. It was not tested before installation...any need to do that because it's OEM? The Carquest thermostat was tested after removed and it was stuck.
 

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The thermostat was replaced twice last year...1st with a Carquest brand, and when car continued to overheat, it was replaced after car driven only a few times with a Mopar that I purchased from the Dodge dealer. It was not tested before installation...any need to do that because it's OEM? The Carquest thermostat was tested after removed and it was stuck.
OEM parts are not 100% immune from quality issues.
 

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Am I properly remembering that these 3.2L and 3.5L engines were upflow systems? If the radiator is cold and the upper hose is warm or hot, (Trying to remember the last comment in the OP), then I suggest a restriction either in the radiator, or that properly installed t-stat.

Saw this on another site. Hopefully, it won't be this involved...

Both Brandon and I posted in that thread. :)

What do you mean by "upflow systems"? I can guess, but, ignoring the heater core loop, the flow is from the intake manifold, thru the upper rad. hose, thru the rad. (from passenger side to driver's side), thru lower rad. hose, into thermostat housing, thru thermostat, into engine block.

Couple of comments:
• That is one of a handful of threads on the 300M Enthusiasts Club forums in which a problem apparently unique to 300M Special engines is mentioned, which was casting slag being left (at the factory) in some of the main coolant passages in or leading to the driver's side head, which over time, either collected together or otherwise clogged in the head passage, causing an almost impossible-to-diagnose overheating problem.
• Reading that thread brings up two other things to consider: (1) Are the radiator cooling fans working properly (I actually meant to mention that in my previous post), and (2) even though the system is "filled", was it filled according to the procedure spelled out in the FSM using the bleed valve and reservoir over-fill method of filling to ensure no air and a reserve volume of coolant in the overflow compartment of the reservoir?

So eagle4x - (besides all the other possible causes already mentioned) was the system properly filled, bleeding the air and overfilling the reservoir as prescribed in the FSM to ensure full displacement if any air in the system and reserve volume of coolant in the overflow chamber of the reservoir?
 

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The both radiator cooling fans operate correctly. When the last repair work was done, the car was idling in the yard while I bled air from the system, checked for leaks. The coolant temperature gauge indicated just above the second line. I'd say thats about 40% scale. It stayed there while the car ran for about 30 minutes. That 40% mark is where my 'trep runs. Air temperature was about 55° F. For the time being, I'm assuming the thermostat is good. Yes, I know about "out of box" failures with OEM parts. Or failures with 5 or 10 miles.
The coolant system was filled according the FSM, except I didn't use Miller Tool xxxxx. However, yesterday, when the car ran hot, I checked for air at the bleeder port. I use a clear plastic hose on the bleeder so I can watch for air bubbles. Ran the engine and it was continuous fluid coming out. No bubbles.
I like the suggestion about squeezing the upper hose to check for a slipping impeller.
 

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Both Brandon and I posted in that thread. :)

What do you mean by "upflow systems"? I can guess, but, ignoring the heater core loop, the flow is from the intake manifold, thru the upper rad. hose, thru the rad. (from passenger side to driver's side), thru lower rad. hose, into thermostat housing, thru thermostat, into engine block.
I don't remember it flowing that way.

I think this is what cased so many t-stats to be installed backwards. Since the flow was from the bottom of the radiator to the top. Which was opposite norm for dozens of makes and models. Since the t-stat was a separate channel from the bypass, in the t-stat housing, coolant was unrestricted to the heater core. I think this was to allow a faster cabin warming.
 

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The both radiator cooling fans operate correctly. When the last repair work was done, the car was idling in the yard while I bled air from the system, checked for leaks. The coolant temperature gauge indicated just above the second line. I'd say thats about 40% scale. It stayed there while the car ran for about 30 minutes. That 40% mark is where my 'trep runs. Air temperature was about 55° F. For the time being, I'm assuming the thermostat is good. Yes, I know about "out of box" failures with OEM parts. Or failures with 5 or 10 miles.
The coolant system was filled according the FSM, except I didn't use Miller Tool xxxxx. However, yesterday, when the car ran hot, I checked for air at the bleeder port. I use a clear plastic hose on the bleeder so I can watch for air bubbles. Ran the engine and it was continuous fluid coming out. No bubbles.
I like the suggestion about squeezing the upper hose to check for a slipping impeller.
Fair enough.

On the fill and bleed, it's not good enough to fill the reservoir and have no air bubbles coming out of the opened bleeder. Because there may be pockets of air trapped in hills and valleys in the system, there may be some air still in the system even though no bubbles at open bleeder. If you don't create a scenario where you somehow force additional coolant into the overflow section of the reservoir, that trapped air won't work itself out on subsequent warm up/cool down cycles (circulating and trapping air thru the reservoir from the heater loop while the engine is running for several minutes at non-idle road speed, and then sucking new excess coolant from the overflow section when it cools back down - resulting in displacement of the last bit of air that would have remained in the ststem if you didn't start out with additional coolant in the overflow section).

I realize you may already realize what I just explained, but I don't know that for sure, so hopefully you understand where I'm coming from in making sure the idea behind the overfill part of the procedure is clear. I know sometimes people get offended when they feel like you're treating them like they're a dumb **** when they're not, but that's not my intent. :)

You can simulate the effects of the special tool by holding a funnel tight (to seal) against the very top of the fill hole of the reservoir with the overflow hose clamped closed with a hemostat (or similar), overfilling into the funnel with a couple cups of coolant, and then releasing the hemostat and allowing the excess coolant to drain thru the overflow tube into the overflow compartment. The trick is figuring out a way to seal the funnel against the tippy top of the reservoir opening, and not down one level below the overflow tube port. You just have to figure out a way to accomplish that if you don't have the special type of funnel to do that. (Another way would be to inject a couple of cups of coolant into the overflow port with a syringe beyond the reservoir already being mostly full.)

HAVING SAID ALL OF THAT, I'm not saying that air in the system is the problem. 🤪
 

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I have to assume that Cruzcar, as a mechanic, probably has one of those funnels that mounts directly on the filler neck of the recovery bottle. If not, then I highly recommend you get one. This type of filler often comes with multiple neck adapters which is helpful for other brands besides the LH.

If I wasn't so digitally lazy, I would post a picture of it.
 

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Fair enough.

On the fill and bleed, ..........................

.........HAVING SAID ALL OF THAT, I'm not saying that air in the system is the problem. 🤪


Even though air is likely not the current issue, I appreciate the bleeding air explanation. Been doing mechanic work for 40+ years, I amaze myself at how dense I can get, sometimes. My nemesis with these LH cars is bleeding the air efficiently. I have a copy of the FSM and will review that.

I'm gonna have to rig up something or get that special tool if I"m going to keep working on these cars.
 

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With this image, I am at a loss to figure out how coolant can move from top to bottom as Peva said. If all the hot coolant was flowing from the top hose and then through the radiator, it would not be able to reach the thermal sensor in the t-stat.
 

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I have to assume that Cruzcar, as a mechanic, probably has one of those funnels that mounts directly on the filler neck of the recovery bottle. If not, then I highly recommend you get one. This type of filler often comes with multiple neck adapters which is helpful for other brands besides the LH.

If I wasn't so digitally lazy, I would post a picture of it.
Well, you assumed wrong. :) I"m a cheapskate sometimes. I really didn't think I needed it for one car. But, now more of these LH cars have shown up on my radar.
.
 

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Well, you assumed wrong. :) I"m a cheapskate sometimes. I really didn't think I needed it for one car. But, now more of these LH cars have shown up on my radar.
.
If I knew where I put it, I'd send you the one I got for my brother. He went through a number of cooling issues on a LH that he had, but had sold the car before I had the chance to give it to him.
 
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