1998 mustang irregular rpm's showing hot - Ford Mustang Forum
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post #1 of 19 (permalink) Old 06-11-2011 Thread Starter
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1998 mustang irregular rpm's showing hot

98 mustang was overheating, jerking, running rough and just not sounding healthty. New wires, plugs,thermostat, Air Filter you name it has been replaced along with a radiator, hoses and battery within the past two months. Once the tune up was completed it jerked a little then ran fine for 10 minutes... It started to shake rpm's became irratic then started to go hot. Lifted the hood nothing was leaking everything seemed fine, everything was just unbelieveably Hot.

When I turn the ac on the car almost dies... Should be hooking it up to a diagnostic in a few days. Was just wondering if anyone had any ideas? Any help, suggestions would be greatly appreciated. Thank you

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post #2 of 19 (permalink) Old 06-12-2011
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How did you bleed the air from the motor? The V6 will overheat unless all of the air is removed from the motor cooling system.

Confirm that the cooling fan runs.

Any "play" in the water pump bearings?

Any blockage in the exhaust system?


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post #3 of 19 (permalink) Old 06-12-2011 Thread Starter
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Water Pump and exhaust seem to be fine. Fan is kicking on at the right time. It doesn't get "hot" anymore... the temp starts to go up but seems to settle (dont want to run it that long) It is idling really hard and doesn't have the same get up and go. And I'm sorry I don't follow the bleeding air thing, could you fill me in?
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post #4 of 19 (permalink) Old 06-12-2011
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So since you don't know anything about how to remove the air from the motor, should we assume that you just put coolant in until it the overflow tank was full?

If so, there is air trapped in the motor and likely this is your problem. Why? The older V6's use a coolant sensor. If the sensor is in contact with air it will read LOW (the sensor is reading the temperature of air and not the coolant). The air also delays the T-stat opening and blocks the flow of coolant.

This is a HUGE problem on the V6. Which is why Ford switched to a CHT sensor in later MY's.

Search on V6 coolant refill procedures.

Should also consider running a compression test.

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post #5 of 19 (permalink) Old 06-13-2011 Thread Starter
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Been reading since you replied to the thread everyone seems to say something different. Does a 98 3.8 L have a bleeder valve? Do I just jack it up... Turn the heater on with the radiator cap off? What you said made complete sense as an explination for everything, just want to know for sure before I do it. Your help is much appreciated. Thanks
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post #6 of 19 (permalink) Old 06-13-2011
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V6 coolant fill procedures

***NEVER run the motor with the motor vent open. This will draw air into the cooling system completely defeating the entire process.

>>
Filling — 3.8L without RADKITPLUS

CAUTION: Vehicle cooling systems are filled with Motorcraft Premium Gold Engine Coolant VC-7-A (in Oregon VC-7-B) or equivalent meeting Ford specification WSS-M97B51-A1 (yellow color). Always fill the cooling system with the same coolant that is present in the system. Do not mix coolant types.

CAUTION: Engine coolant provides freeze protection, boil protection, cooling efficiency, and corrosion protection to the engine and cooling components. In order to obtain these protections, the engine coolant must be maintained at the correct concentration and fluid level in the degas bottle.
When adding engine coolant, use a 50/50 mixture of engine coolant and deionized water.
To maintain the integrity of the coolant and the cooling system:
Add Motorcraft Premium Gold Engine Coolant VC-7-A (in Oregon VC-7-B) or equivalent meeting Ford specification WSS-M97B51-A1 (yellow color). Use the same coolant that was drained from the cooling system. Do not mix coolant types.
Do not add/mix orange-colored Motorcraft Speciality Orange Engine Coolant VC-2 or equivalent meeting Ford specification WSS-M97B44-D. Mixing coolants may degrade the coolant's corrosion protection.
Do not add alcohol, methanol, or brine, or any engine coolants mixed with alcohol or methanol antifreeze. These can cause engine damage from overheating or freezing.
Do not mix with recycled coolant unless it meets the requirements of Ford specification WSS-M97B51-A1. Not all coolant recycling processes meet these Ford specifications. Use of such coolants can harm the engine and cooling system components.
NOTE: The addition of Motorcraft Cooling System Stop Leak Pellets, VC-6, darkens Motorcraft Premium Gold Engine Coolant from yellow to golden tan.
1) Place the heater temperature selector in the maximum cool position.

2) CAUTION: On 3.8L engines, the vent plug must be removed before radiator fill or the engine may not fill completely.
NOTE: It is important to maintain engine coolant concentrate between 40 percent or -24C (-11F) and 60 percent or -52C (-62F).
Fill the engine cooling system with 50/50 mixture of water and engine coolant.

3) After filling the engine cooling system, add coolant to the vent until full. Install the vent plug.

4) Leave the pressure relief cap off and run the engine until it reaches normal operating temperature.
5) Stop the engine and add the correct engine coolant mixture to the degas bottle/coolant expansion tank until the coolant level is between the COOLANT FILL LEVEL marks.
6) Turn the engine off and allow the cooling system to cool. Check the level in the degas bottle/coolant expansion tank, and add a 50/50 mix as needed.

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post #7 of 19 (permalink) Old 06-13-2011 Thread Starter
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There is quite of corossion build up on the radiator cap and down the radiator, would be best to flush the entire system as well?
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post #8 of 19 (permalink) Old 06-13-2011 Thread Starter
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The vent plug will not even loosen, there is no give on the damn thing

Last edited by napolez; 06-13-2011 at 03:30 PM. Reason: typo
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post #9 of 19 (permalink) Old 06-13-2011 Thread Starter
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15 mm did the trick, I'll repost with an update, thanks for all the knowledge.
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post #10 of 19 (permalink) Old 06-13-2011 Thread Starter
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Update: Got it flushed, got the air out of the coolant system... started right up, idled great.Took it down the road for about 10 minutes, car started to rattle again with the rpm's real touchy. Opened the hood my overflow tank was Boiling... Boiled for about 5 minutes, then the radiator sucked it all up. Really thick dark brown reddish corosion in both tanks. Does this mean water pump?
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This could be:

Bad radiator cap. Not holding pressure.

Clogged radiator. But since the radiator has been replaced, this seems unlikely.

Incorrect anti-freeze percentage. Too much anti-freeze or too much water.

Bad T-stat or T-stat installed backwards.

Cooling fan not running.

Blocked exhaust.

Bad head gasket or cracked block. Run a compression check. Perform a cooling system pressure test.

Bad water pump. Check bearings for play. Any coolant from the weep holes?

Based upon all the stuff already replaced, the general poor running of the motor, and the fact it has overheated in the past points to more serious base motor issues.

Running a coolant system pressure test will let you know if there is a bad head gasket.

A compression test will also help narrow this down.

There is also a test for hydro-carbons in the coolant. This would indicate a bad head gasket.

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2000 GT coupe (Craigslist project. Fixed. Now my DD). Windsor to Romeo swap.
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Here's a picture of the V6 vent tube just in case you don't know where it is.
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2003 GT Convertible (sold & missed)
2000 GT coupe (Craigslist project. Fixed. Now my DD). Windsor to Romeo swap.
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i think thats what the problem was with mine but a bit different. my car was idling and running fine, but after about 10 minutes i could watch the thermostat just climb until it was almost red lining. when i would pop the hood the coolent in the rad would be boiling, fans were on, and after about 5 or so minutes all the coolent would be out of the radiator and in the overflow tank. i would add more coolent and same thing. also my heat would blow cold constantly except when i would stop after it had been running hot and add coolent to proper level heat would blow for a few minutes then back to just air. any sugestions
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Just wondering if you realize that every time the coolant boils over this creates air inside the motor? As such, the V6 coolant re-filling procedure needs to be repeated.

When working on cooling system problems, the first step should be to confirm that the cooling system is in good repair.

Then rule in/out a blown head gasket.

2003 GT Convertible (sold & missed)
2000 GT coupe (Craigslist project. Fixed. Now my DD). Windsor to Romeo swap.
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post #15 of 19 (permalink) Old 03-26-2013 Thread Starter
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turns out it was a blown head gasket. got it re machined and it ran like a beast after that.

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98 mustang , irratic rpm's , weak idling

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