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Mark, Auto Service Technician
Category: Car
Satisfied Customers: 11332
Experience:  22 Years Experience...Factory Trained and Certified
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300M: temp gauge..water pump, timing belt, radiator..temp sensor

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While driving my 300M a 3.5L, and very suddenly temp gauge went high, pulled over to check and the engine was very hot. I brought it to my local dealer, and they replaced the water pump, timing belt, radiator, radiator cap, temp sensor and thermostat. All of these parts were replaced several times with the new Mopar parts, and my car is still over heating. They even performed a cylinder leak down test, twice and the test didn't show any signs of head gaskets being bad. There are no bubbles present in the overflow tank. The car doesn't lose any coolant. The upper hose gets very hot and the fans turn on when they're suppose to, but for some reason the lower hose stays cold. They cleaned all the coolant passages by flushing the system with a cleaner. But if we remove the thermostat, the car doesn't overheat, and you can feel both hoses getting hot and you can feel the circulation going well. They're saying they also did a combustion leak test, and it showed no gasses in the coolant system. At this point they don't have any ideas as to what might be causing this problem. I already paid them over $2200, and it's still a mystery! Any help from experts like you would be very appreciated!!! Thanks in advance.
I distinctly remember having an identical problem with one of these in our dealership.

Every test we did, passed, and the source of this issue was eluding everything we tried...................much like your situation.

After replacing many parts and double and triple checking everything, we opted to pull the cylinder heads off and have them checked by a machine shop for potential cracks even though we had no indication there might be it seemed to be the only thing that it could be.

The end result, was that one head had a very small crack that was not detectable using the normal methods. After replacing that head, the problem was cured.

I hope this information is helpful and let me know if you need further assistance with this.

Mark and 2 other Car Specialists are ready to help you
Customer: replied 5 years ago.
Thanks for the info. So you are very positive that is what's causing this cooling system problem on this 3.5L engine? Were you guys able to see that problem, as soon as you pulled the heads? Would you think that a bad lower intake manifold gasket can be bad, that might also cause this over heating, because it does have coolant passages? Just thought I ask...
I'm only relaying a personal experience that is virtually identical to the one you are describing. We had exhausted all other options, so the process of elimination theory led us to beleive the problem was going to be with one of the heads or head gaskets.

We weren't able to see the crack initially, so that is why we sent it to a machine shop and they were able to locate the crack with the equipment they have.

If the intake was leaking you would be having an external leak, that should either be visible or at least leave some staining on the outside of the block to indicate the presence of a leak.

I hope this information is helpful and let me know if you need further assistance with this.

Mark and 2 other Car Specialists are ready to help you
Customer: replied 5 years ago.
What can also be the cause of no coolant circulation in the cooling system? By that, I mean, the lower hose stays cold. Thanks.
That is what happens when there is a combustion chamber leak into the cooling system from a head issue or head gasket issue.
Customer: replied 5 years ago.
So once I pull the heads off, and scrape the old gaskets off, how would I know if the engine block is warped? Even though I will have the heads checked out by a machine shop specialist.
I've never seen a block get is always the head.

Customer: replied 5 years ago.
Is there a special way to tell if the block is cracked, after the heads are pulled off?
Not without pulling the engine out, and sending it to a machine shop for testing.

There isn't anything you can do yourself aside from a visual inspection, but having said that you aren't likely to "see" anything because the leak you have is so small.

There are a variety of crack inspection techniques that can be used by themselves or in combination with other techniques to find cracks in castings and other components. These include magnetic particle inspection, various types of penetrating dyes, pressure testing, vacuum testing, ultrasonic (acoustic) testing and even x-rays.

I hope this information is helpful and let me know if you need further assistance with this.

Customer: replied 5 years ago.
I just had the heads resurfaced on Dodge Intrepid 3.5L. Everything was put back the way it came off. I had to remove the cams sprockets to remove the heads! How do I reset the cams so that I can start the car for the first time?
The is a special tool that needs to be bolted to the rear of the camshaft to lock it in place before the sprockets are tightened to the cam. You will either need to try and rent these locally or purchase them to finalize the installation.

The tools are number 7999 in the following document.

Customer: replied 5 years ago.
I have that tool, but it seems like its only made to hold the cams in place when you're tightening the sprocket bolts. But it's not meant to guide me in the right direction to make sure that i set both cams in there neutral position. Some illustrations tell me to set Top Dead Center on the crank and then align both cams in between the two dotted marks and it should start. Then others show that the passenger cam sprocket in the middle and driver's cam sprocket 45 degrees from the center dotted lines! Please advice me.
Both cam marks need to be in between the 2 dots.

Customer: replied 5 years ago.
So you're saying that is the correct way to align after everything was apart? Even though the number one cylinder is in front on passenger side, and when the driver's side is also aligned in the center as well, that won't cause the valves to bind? Then why do the other websites show the driver's side sprocket showing 45 degrees clockwise from the center?
Yes, there is only one way to line these up and that is the pic I sent you.

I don't know what else you're looking at, but if it is different than my pic, then it is not for this particular engine.
Customer: replied 5 years ago.
Ok I'll try setting it up by following your picture. But that other illustration that I was talking about is from a Haynes repair manual for the 3.5L Chrysler/Dodge engines.
Ok, let me know if you need anything else.
Customer: replied 5 years ago.
When I try to move the "left" cams procket to line up between the two dots on the back of the timing cover, what I notice is that two intake valves are open and two exhaust valves on this cylinder head. Is that actually normal?
Yes it is.

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