Shaky on startup

[ijag]

For the longest time my 99 v6 ohv explorer shakes for like 10 seconds after a cold start but after it’s warmed it don’t do it and runs fine. I thought maybe a bad iac?
Over the past 3 years this is what I have done to it:
Intake gasket
Radiator
Heater valve
Fuel filter
Fuel pump
Starter
Spark plugs
Plug wires
Coil
02 sensors

 

[koda2000]

For the longest time my 99 v6 ohv explorer shakes for like 10 seconds after a cold start but after it’s warmed it don’t do it and runs fine. I thought maybe a bad iac?
Over the past 3 years this is what I have done to it:
Intake gasket
Radiator
Heater valve
Fuel filter
Fuel pump
Starter
Spark plugs
Plug wires
Coil
02 sensors

The OHV engines are prone to cracking their heads between the valve seats. It could be you have a hair line crack that seals as soon as you get some heat in the head. If this is the case, some here have had success adding a product called K-Seal to the cooling system. Only other option is to replace the head(s) which may be worth it. It's not too expensive or hard to do, but that's up to you. The OHV V6 is a pretty bullet proof engine other than the heads cracking.

 

[974X4BLACKSPORT]

Put a vacuum gauge hooked up to full manifold vacuum at cold at cold start and observe the needle and the amount of vacuum created during those first few seconds after the cold start.

 

[ijag]

The OHV engines are prone to cracking their heads between the valve seats. It could be you have a hair line crack that seals as soon as you get some heat in the head. If this is the case, some here have had success adding a product called K-Seal to the cooling system. Only other option is to replace the head(s) which may be worth it. It's not too expensive or hard to do, but that's up to you. The OHV V6 is a pretty bullet proof engine other than the heads cracking.

Are there any pages you could direct me to for replacing the heads, thanks

 

[koda2000]

Are there any pages you could direct me to for replacing the heads, thanks

IDK that anyone has ever posted a tutorial on the subject. There's probably several video on YouTube. @974X4BLACKSPORT can probably help you.
Before jumping into changing the heads do as he suggested regarding checking engine vacuum at cold start and compare the readings as the engine begins to warm up.

 

[ijag]

Put a vacuum gauge hooked up to full manifold vacuum at cold at cold start and observe the needle and the amount of vacuum created during those first few seconds after the cold start.

Thanks, will try this

 

[ijag]

IDK that anyone has ever posted a tutorial on the subject. There's probably several video on YouTube. @974X4BLACKSPORT can probably help you.
Before jumping into changing the heads do as he suggested regarding checking engine vacuum at cold start and compare the readings as the engine begins to warm up.

Say if it was the heads, would using the k-seal be safe to use or is there some risk in it

 

[donalds]

Never ANY risk using K- seal at ANY time ever

 

[koda2000]

Zero risk with using K-Seal.

 

[masospaghetti]

Are you losing a little bit of coolant over time? It could be a little as a few cups or so every few months. IMO this would strongly suggest a cracked head.

I'm in the process of replacing both heads right now (had the symptoms you described, found a crack in cylinder 4). Happy to help if you have any questions.

Edit: I'll see if I can put together a step-by-step for re-installation since there doesn't seem to be one.

 

[ijag]

Are you losing a little bit of coolant over time? It could be a little as a few cups or so every few months. IMO this would strongly suggest a cracked head.

I'm in the process of replacing both heads right now (had the symptoms you described, found a crack in cylinder 4). Happy to help if you have any questions.

Edit: I'll see if I can put together a step-by-step for re-installation since there doesn't seem to be one.

Yeah I lost some coolant Over the last few months, but I seen my heater core valve was leaking so maybe it was from that? I replaced it and I will check to see if I lose anymore over the next month or 2.
And please the step by step instructions would be of big help

 

[masospaghetti]

Yeah I lost some coolant Over the last few months, but I seen my heater core valve was leaking so maybe it was from that? I replaced it and I will check to see if I lose anymore over the next month or 2.
And please the step by step instructions would be of big help

I'd recommend going to an Autozone and getting their free rental coolant testing kit. It allows you to pressure test your system when it's cold and when the engine isn't running. This is a huge help in finding small coolant leaks.

Not only is it much safer to work around an engine that isn't running (and hot), but small leaks can evaporate due to the hot surfaces before they are easily detected.

Definitely rule out a small external leak before you tear into the motor. Using this method I found a small leak at 3 of the hose connections due to weak factory clamps that I would have never found otherwise.

 

[ijag]

I'd recommend going to an Autozone and getting their free rental coolant testing kit. It allows you to pressure test your system when it's cold and when the engine isn't running. This is a huge help in finding small coolant leaks.

Not only is it much safer to work around an engine that isn't running (and hot), but small leaks can evaporate due to the hot surfaces before they are easily detected.

Definitely rule out a small external leak before you tear into the motor. Using this method I found a small leak at 3 of the hose connections due to weak factory clamps that I would have never found otherwise.

I never used the coolant tester will that rule out a cracked head if it is cracked? Or just hose leaks ect.

 

[koda2000]

Yeah I lost some coolant Over the last few months, but I seen my heater core valve was leaking so maybe it was from that? I replaced it and I will check to see if I lose anymore over the next month or 2.
And please the step by step instructions would be of big help

That's what the K-Seal might help you with. If it stops the leak into the cylinder the problem goes away (at least for a while) and as long as the crack is sealed and doesn't expand, a while can be a very long time. The nice thing about K-Seal is that it remains active in the cooling system to seal future leaks and that it will not clog anything. Certainly worth a try. It stopped a leaking timing cover gasket on one of my 5.0L's and it's hasn't leaked again in probably 5-6 years. I'm planning on flushing the cooling system in that truck this spring and I'll be adding another bottle of K-Seal to it afterwards.

 

[donalds]

I used it it stopped a water pump leak believe it or not
I put a bottle in my new cooling system just because it works so well

 

[koda2000]

If your engine is stone cold and you pressurize the cooling system it should force coolant into the offending cylinder, which will show a loss of pressure, though it may be small.

I'm 95% sure you have a cracked head. The symptoms you report are spot-on for the 4.0L OHV cracked head.

 

[Turdle]

The K seal is a speculative fix no? Have you verified vacuum at cold start compared to warmed engine?

Here's how I would attack the cold start coughing

clean IAC and MAF
Change air filter. Change PCV valve.

Check engine vacuum. Low vacuum when cold means the intake gaskets are hardened again.
Pull spark plugs and read them for signs of coolant being leaked into combustion chamber.

Then, if evidence of cracked head was found use the k seal.

 

[masospaghetti]

I never used the coolant tester will that rule out a cracked head if it is cracked? Or just hose leaks ect.

It will definitely help you find external leaks. If the head crack is bad enough you may see coolant show up in the bad cylinder during the test. (Mine did not show any coolant in the cylinder.) This brings up a good point, that you should check each cylinder after this test by pulling the plugs to make sure you didn't fill it up with coolant.

 

[koda2000]

@Turdle -The OP has been advised twice to begin with checking engine vacuum at cold start and as the engine warms.

I agree that K-Seal would be speculative at this point, but it wont hurt anything either.

 

[ijag]

-Ok I will use the vacuum gauge First what hose is best to use the gauge on the 4.0 v6 ohv?
-After that I will look for coolant leaks with coolant tester if none are found I will use k-seal until it warms up and then I will replace the head
@masospaghetti looking forward to the step by step on replacing it