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Temperature gauge fluctuating

Kevin Tinoco

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I have a 1996 Explorer 4.0 with 292k miles and i have been having this problem for a few weeks ever since I got the head gaskets replaced where once the temp gauge gets close to half it would drop down to about 1/8 and then it would go up and down again,it will always be fluctuating in that area.
Parts I have replaced since then are:thermostat,coolant temperature sensor,temperature sending unit,water pump,radiator, and radiator cap and it is still fluctuating. I don’t know what else it could be at this point.
 


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koda2000

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Might be a cracked head.
 








koda2000

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Would that cause white smoke to come out of the exhaust? Because I don’t see any

Not necessarily. White smoke means your getting coolant into the combustion chamber. If you're getting exhaust into the cooling system it can cause temp fluctuations, because the temp sender and sensor do not read correctly when they're not constantly submerged in coolant.
 




Kevin Tinoco

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Not necessarily. White smoke means your getting coolant into the combustion chamber. If you're getting exhaust into the cooling system it can cause temp fluctuations, because the temp sender and sensor do not read correctly when they're not constantly submerged in coolant.
So if it has a cracked head like you say do you think that k seal would work?
 




koda2000

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So if it has a cracked head like you say do you think that k seal would work?

No, no sealant will work when you're leaking exhaust into the coolant. If you're leaking coolant into the combustion chamber maybe it would work, but if exhaust into coolant, you're talking about 160 PSI of cylinder pressure going into 16 psi of coolant pressure.

K-Seal customer support says that if you can run the offending cylinder with the spark plug removed for 20-30 mins their product might work, but I still doubt it. You should have had the cylinder heads checked by a machine shop before reinstalling them after the head gasket replacement. The 4.0 OHV heads are prone to cracking, especially after overheating. Machine shops have ways of checking for cracks (through a process called magna-fluxing) which can be very hard to see with the human eye. A crack between the valve seats is not uncommon.

There are also ways to test your coolant for the signs of exhaust (bubbles periodically burping into the expansion/reserve tank). There is also a way to test the coolant itself.
 




96eb96

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So if it has a cracked head like you say do you think that k seal would work?
I have the same truck as you and k-seal worked fine for me. Stopped the floating gauge too. Maybe the head gasket wasn't installed correctly or the head wasn't inspected properly for cracks when you originally had the problem. Offending cylinder may also crack the plug. Do you have any misfires?

YMMV.
 




Kevin Tinoco

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I have the same truck as you and k-seal worked fine for me. Stopped the floating gauge too. Maybe the head gasket wasn't installed correctly or the head wasn't inspected properly for cracks when you originally had the problem. Offending cylinder may also crack the plug. Do you have any misfires?

YMMV.
I have no misfires it runs good but I forgot to say that the coolant level also drops every morning I have to top it off so would that still be a cracked cylinder head?
 




Kevin Tinoco

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I have the same truck as you and k-seal worked fine for me. Stopped the floating gauge too. Maybe the head gasket wasn't installed correctly or the head wasn't inspected properly for cracks when you originally had the problem. Offending cylinder may also crack the plug. Do you have any misfires?

YMMV.
I have no misfires it runs good but I forgot to say that the coolant level also drops every morning I have to top it off so would that still be a cracked cylinder head?
 




96eb96

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No

I have no misfires it runs good but I forgot to say that the coolant level also drops every morning I have to top it off so would that still be a cracked cylinder head?
Mine was like that for a long time, lost a bit of coolant(not every day though), eventually there were terrible misfires. Suggestion is to get forscan software (free for your pc) and an OBD II adapter (BAFX one works well for these trucks) and monitor the individual cylinder pids for misfire. The bad cylinder will be an outlier. You may see 20 where the others have 2-5. You will not notice this when you drive because the crack is very tiny, but coolant is getting in. Another thing is to drain off some coolant, and see how much it rises in the radiator when it starts up.

You could have other external leaks, like the freeze plugs or lower intake gasket.
 




Kevin Tinoco

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Mine was like that for a long time, lost a bit of coolant(not every day though), eventually there were terrible misfires. Suggestion is to get forscan software (free for your pc) and an OBD II adapter (BAFX one works well for these trucks) and monitor the individual cylinder pids for misfire. The bad cylinder will be an outlier. You may see 20 where the others have 2-5. You will not notice this when you drive because the crack is very tiny, but coolant is getting in. Another thing is to drain off some coolant, and see how much it rises in the radiator when it starts up.

You could have other external leaks, like the freeze plugs or lower intake gasket.
Well I have put a cardboard under the truck multiple times overnight and while idling and I see no external leaks,but I will consider everything you have said and hopefully I can find out what the problem is,and another thing is that the other day I started it when it was cold and it ran for about 3 minutes it was still cold and I opened the radiator cap to check the coolant level and coolant came out like crazy,there was too much pressure so I’m guessing that’s more evidence for a cracked head
 




fast_dave

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Kevin Tinoco,

Just saying since it's simple, costs $0.00, and I haven't seen it mentioned.

Have you turned your heater on while filling your cooling system and after it's topped off, taking a few laps around town - with the heater on - so as to purge the air in the cooling system which was introduced when the head gasket was replaced?
 




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