99 4.0 ohv extended cab auto 4x4

[kevinmcgowan25]

Hi all I am looking for some serious advice. Currently having an overheating issue, all cooling system components have been replaced by me and are functioning properly. Passes the glove test but is blowing off the top radiator hose. Plan to run truck to operating temp with no cap then try the glove test, cold there is no bounce. I recently changed the timing chain sprockets and guide. Decided to run a compression test to try and find something to work with. bank one all cylinders came up 120 cold and dry. bank two 4=105 5=95 6=120. Then I put some oil in number 5 and it shot up to 150 haha. Bad ring maybe? Wondering do you think I could be off a tooth on the chain. Truck already has aftermarket heads. The truck runs and drives normal, idles fine develops what seems to be a single cylinder miss once it gets hot and starts to overheat. Ive been very careful the trucks gauge has never been past 3/4 and it does work properly had issues previously with the sender but have fixed. The truck has no o2 and is straight piped with 2.5 pipe dual exhaust idles about 1000 cold then drops down a bit once warmed up. I have already rebuilt the entire frame and cab so I plan to keep the truck regardless. I have a leak down test.

 

[RonD]

The heater hoses are the water pump by-pass on this cooling system, so they always need good flow between them

One hose is at the top of engine by thermostat housing, coolant flows out from that hose and thru the heater core and then back to the engine on the other hose, connecting to the water pump
If heater core is plugged up or "by-pass valve" is, then you can get overheating
You can simply loop one of the hose between thermostat and water pump or otherwise connect the two hoses together to see if thats the issue

Compression numbers are very low, but that would cause less power not overheating
Expected is 145-155psi on a 4.0l OHV

No, on the timing chain, 4.0l OHV never had timing chain issues, the 4.0l SOHC did, different engines, but both used in Rangers
4.0l OHV was 1990-2000
4.0l SOHC was 2001-2012


Cooling systems normally run at 14-16psi internal pressure after warm up, that's the rad caps main valve rating, it prevents hoses from "blowing off"
So even it engine is overheating hoses shouldn't "blow off"
The overflow tank would fill up and "overflow" maybe

All liquids expand in volume when heated, just physics
A gallon of coolant at 70degF becomes a 1.25 gallons at 200degF, this is where the internal pressure in the cooling system comes from
So if you run the engine without rad cap coolant should start to overflow from the rad cap opening after about 5-7 minutes as it expands, that normal
If it starts to overflow and continues to overflow as soon as you start the engine then you have a blown head gasket or cracked head, undetected by glove test, which is odd

Blocked radiator tubes and water pump issues also cause overheating

 

[alwaysFlOoReD]

You replaced the water pump? I had an overheat problem and it turned out the impeller had come off the shaft.

And now that I reflect on it, I had frozen the block by having straight water... and fired it up while frozen...oops.

 

[kevinmcgowan25]

The heater core was flushed and flows, new bypass valve have already confirmed it flows. Yes water pump was replaced, belt is routed correctly there is flow through radiator had replaced that and the new one had the seal bust from this unexplainable pressure in the cooling system. This is why I don't understand how the engine is not failing the glove test as there is a insane amount of pressure enough to physically cause the hose to leak and blow off. The combustion leak is not caused until the engine is warm, wouldn't it be the opposite as when the engine heats up it would be less? The cap is not the problem the coolant travels into the overflow tank the coolant is getting steamed. I have always bleed the cooling system properly removing a heater hose and filling until it spills out there is always air in the system aftercool down always a little bit of coolant missing from the system. Seems to be physically steaming itself. Crank cog had two broken teeth back to back and on first start the chain was always noisy on this 4.0 ohv. All keyways lined up when changing sprockets for timing chain.

 

[kevinmcgowan25]

Low compression is why I was mentioning if the chain could be off a tooth, but truck still runs and drives normal so made no sense to me I have another gauge I will try but there is no account for cylinder 5 being down 30 from the rest either way if the gauge is off. No coolant and oil mixing.

 

[RonD]

Remove one of the heater hoses at the firewall when refilling cold engine, that lets out all the air from the engine side
When coolant/water starts to come out hose and core put hose back on
No burping needed

Top up radiator leave cap off
Start cold engine
Should be a burp of coolant/water from cap opening, but that's it
If coolant/water continues to flow up and out of rad cap opening then blown head gasket or cracked head