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theksmith

overheat, did i blow my 4.7L engine?

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engine runs, yay! idles smooth, no smoke from exhaust. currently optimistic.

 

filled her up correctly with water, let it idle for a while and no problems. letting it cool down now. then i will take her for a spin around the block and see what happens.

 

if everything seems ok, i'll have to change the oil and flush the cooling system again with a correct 50/50 mixture (as currently it's just water). then i might look at doing the blok check thing just to feel confident that there are no looming problems. anything else i should do?

 

here's what i think i've learned so far - on the 4.7L, you can fill the radiator all damn day long till it pours back out and you aren't filling the engine with coolant at all. the thermostat is on the bottom and closed when cool, so you aren't getting coolant into the engine that way. then the upper radiator hose actually goes into the engine higher than the radiator, so you aren't getting any coolant into the engine that way unless you have water that pours uphill.

 

the correct way to refill a completely empty 4.7L according to the FSM is first via the "coolant bleed" screw (near where the upper radiator hose goes into the engine), then when that pours back out, re-insert the screw, then add coolant via the radiator filler neck till it pours out, then put the radiator cap back on, then fill the coolant reservoir, then bring the engine up to operating temp, then let the engine cool down and it will suck any more needed coolant from the reservoir, then top off the reservoir again... done.

 

i didn't know all that and thus only filled the radiator after the initial coolant loss, thereby not putting near enough water into the system to get it even half-ass flowing again, and let it overheat a second time. i, nor the computer, knew it was overheating the second time though because the temp sensor is between the "V" in the engine at the top, and needs some coolant flowing over it transferring heat from the engine in order to sense the real temp of the engine. thats why the temp gauge stayed ok yet the engine got hot enough that it couldn't turn over any more and died.

 

also, the 4.7L has aluminum heads that are prone to warpage during an overheat, so at this point, if things are good, then i'll have been very lucky.

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drove around for 20 minutes without problems. and no signs of water in the oil :)

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Oh thank goodness I finally exhaled.

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Good to hear. Fingers crossed.

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drove around for 20 minutes without problems. and no signs of water in the oil :)
I'd still have a pressure test run on the cooling system, and a compression test run, to make sure you do not have a head gasket issue... Better to find out BEFORE you get out in the boonies a long way from a tow...:(

 

Also, I'd suggest you watch the coolant AND oil levels closely for the next few days/weeks...;)

 

Fingers crossed for you that you did not seriously overheat and damage it...;)

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Ditto on still running all the tests. Congrats, seems so far so good!

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You can do a compression test but you could also just pull the plugs and crank the engine with the Fuel injection fuse removed to see if any coolant shoots out. Lay newspaper outside the spark plug holes if it gets wet spots you know that hole is getting water from somewhere.

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Also watch your radiator once overheated if it's got plastic tanks like the tj's they are extremely prone to cracking after an overheat. They'll start out really small then after a couple days can grow to be 3-4 inchs. By that time its spewing onto your driveway again.

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so far everything continues to be ok.

 

my rigged draincock is holding. thought i finally got the $8 back-ordered draincock from Jeep. I'm keeping it and some extra water in the jeep for now.

 

Joe at Absolute Offroad said to watch for:

- oil in coolant (already knew)

- coolant in oil (already knew)

- rough start/idle on first start first thing in the morning (due to possible coolant system at pressure pushing coolant into cylinder thrugh a crack or warped sealing surface while it sits)

 

i have none of those issues, so his point was why even check compression? if we find something a slight bit off, then do i have over a grand to put in new HO heads right now - nope! and if there is something major wrong, then at least one of the above symptoms would show itself.

 

so for now it looks good, and hopefully i didn't take too many years off it's life!

 

i did change the oil and put in some Z-Max. i'm not usually one for additives or particular brands of oil, or for any mystery/magic stuff. but i thought perhaps something was in order due to the likelyhood that i had done 2 things when overheating: 1 - baked some sludge all over the engine's internal goodies, 2 - slightly scored cylinder walls or other surfaces from the fact that the oil at high temperatures breaks down and doesn't really lubricate correctly anymore.

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