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fmw
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Mar 12, 2024, 10:39 AM
Post #1 of 10
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Overheating Mercury
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My 2001 Mercury Marquis is overheating. I flushed the cooling system and replaced the coolant and thermostat without it solving the problem. My question is about how to troubleshoot to determine whether the problem is the water pump or radiator or something else. OBD scan simply reports cylinder head overheating. What do I do next? Thanks for any help.
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Hammer Time
Ultimate Carjunky
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Mar 12, 2024, 1:13 PM
Post #2 of 10
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Re: Overheating Mercury
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Under what conditions does the problem occur? Is it more of an idle problem or when cruising at 40MPH or higher?
Does using the AC change anything?
How many times you you gotten it real hot?
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fmw
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Mar 12, 2024, 2:04 PM
Post #3 of 10
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Re: Overheating Mercury
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The first occurrence was Friday. I drove 15 miles to the supermarket and half way home I had was seemed like an electrical failure. Nothing worked other than the engine which labored. I got it home safely. On saturday I took the other car to the auto parts store and bought coolant and a thermostat. On Monday I flushed the system and replaced the coolant. I checked with the OBD scanner and got the cylinder head overheating code. I erased the code and took the car for a test drive. After 15 miles the temp gauge began rising past the mid point. I was then 2 miles from home and it is sitting in my driveway. The engine runs normally until it overheats.
Haven't used air conditioning yet this year. I can go out now start it up and get 15 normal miles. That's it. The radiator drains normally and completely. It takes 1 3/4 gallons to fill the system with coolant and that is correct. So maybe no blockage there. I'm wondering if it is the water pump. If coolant isn't circulating it should behave just like it does. Is there a way to troubleshoot the pump without replacing ii?
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Hammer Time
Ultimate Carjunky
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Mar 12, 2024, 2:13 PM
Post #4 of 10
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Re: Overheating Mercury
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Your biggest concern right now is whether permanent damage was done when it overheated. It only takes once.
First, make sure you have gotten all the air pockets out of the system first. This is not easy to do sometimes.
Fill the system with coolant and then drive the car until it reaches normal operating temp. The park it and let it cool COMPLETELY. I mean ice cold. Then check the coolant level and top it off accordingly. Repeat this process as many times as necessary until it doesn't take any more coolant when fully cooled off.
In the future understand that coolant flushes and thermostat replacement rarely have any effect on an overheating problem and shouldn't be you first move. There is another cause somewhere. All doing that does is set you up for air pockets you may not have had before.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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fmw
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Mar 12, 2024, 3:10 PM
Post #5 of 10
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Re: Overheating Mercury
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When I filled the system I poured the coolant into the thermostat housing until it wouldn't take more. Then I filled the reservoir. I checked this evening and the reservoir was empty. I'll get more coolant tomorrow when I'm out. I'm now thinking it isn't the water pump either. I remember when flushing the system I left the thermostat housing loose. When I gave it a little gas coolant would come out of the top of the thermostat housing so there is little doubt that coolant is circulating. There are no DTC's on the OBD scan now so I'm baffled. I'll come back when I can complete your instructions.
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Hammer Time
Ultimate Carjunky
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Mar 12, 2024, 3:26 PM
Post #6 of 10
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Re: Overheating Mercury
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In 50 years in this business I have never seen a water pump be the cause of overheating (without leaking) unless they left water in the cooling system for years and the system was so bad the fins rusted right off.
Forget the codes. You can't fix overheating with a code reader.
Your first priority is to get all the air out of the system and then see how long it lasts before overheating. in my experience this is most commonly caused by a slow leak that slowly reduces the coolant until there isn't enough to keep it cool. The big problems develop when you don't realize it soon enough and cause engine damage. Then the problem just keeps coming back worse and worse.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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fmw
Novice
Mar 13, 2024, 10:58 AM
Post #7 of 10
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Re: Overheating Mercury
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I know the cause of the overheating. The system is losing coolant. The reason, I believe, is a leaking or blown head gasket. I believe it because I saw steam exiting the left side of the hood. I don't want to do this repair myself so I have deposited the car with the local mechanic for the fix. I appreciate your help. Keep up the good work.
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Hammer Time
Ultimate Carjunky
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Mar 13, 2024, 11:36 AM
Post #8 of 10
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Re: Overheating Mercury
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No, steam exiting the hood does not indicate a head gasket problem.
It indicates a leak in the cooling system. You need to have the cooling system pressure tested to find that leak and repair it.
I'm not saying you definitely don't have a blown head gasket in addition to the leak. I'm just saying the steam you saw was not an indication of one.
The engine you have is notorious for cracking the plastic intake manifold which is not that serious to repair.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
(This post was edited by Hammer Time on Mar 13, 2024, 11:37 AM)
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fmw
Novice
Mar 25, 2024, 3:14 PM
Post #9 of 10
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Re: Overheating Mercury
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As it turns out, the leak was at the water pump.
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Hammer Time
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Mar 25, 2024, 3:20 PM
Post #10 of 10
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Re: Overheating Mercury
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Yep, pretty common failure
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