Blown Core Plug

aeo

Well-known member
300 Tdi. Ran fine all day- normal EGT, normal oil pressure, normal oil temp, normal coolant temp. Parked it after a 45 min drive. Smoke from under the hood. Blew the rear most core plug- on the left side of the block. Completely out. No damage to it, looked like it just fell out. It was replaced about 4 years ago with the engine install/re-build.

Truck is parked outside and hasn't been driven in 6 days, but the front core plug heater was plugged in all the whole time so I can't imagine it froze at any point. And it was in the high 40's today.

Thoughts on what could cause this?

Thanks,
Alex
 

aeo

Well-known member
Seemed fine last time I was under the hood. No weeping, smooth surface.

Its not threaded, it's smooth.
 

aeo

Well-known member
Looks like it was just hammered in. No sealant on the side of the plug. I didn't install it. Mechanic who did 300tdi conversion did.
 

javelinadave

Administrator
Staff member
I'm no expert but what I'm reading is that people put some type of liquid gasket when installing. Perhaps that is your issue????
 

Grnrvrs

Well-known member
If you know that the coolant did not freeze, then there must have been some other form of pressurization that forced the plug out. Two other forms of pressurization could be from over heating it (particularly with a crap rad cap) or a blown head gasket that is allowing combustion pressure into the water jacket.

You say that the temp was normal. Do you know the actual temp?
 

Jeff B

Well-known member
You're talking about the freeze plug closest to the firewall?

I replaced that one last year.
Just a smear of gasket stuff ( orget what kind) and gently tap it in.
I had to remove the starter to get good access on a the Disco-style 300Tdi but that wasnt much of a job.



.
 

aeo

Well-known member
The operating temp was under 200, when I looked at the Madman after I figured out what happened there were no high markers and no alarms had gone off. When I was driving it I did see my EGT was at 1050 for a minute and then I did notice that my oil temp what as 219, it's normally under 200.

I am talking about the one closest to the fire wall. It was just resting below the hole, I would think it if blew from pressure there would be some force to that. The plug looked new, just dirty.

I'm kind of wondering if this is related to the head gasket. At the end of a road trip this summer I had it leaking oil from all kinds of places. I wonder if it overheated and I didn't know it. I had two coolant gauges then- the Madman and the stock one and neither said it was overheating.

Or I'm paranoid and it's just fine and a weird fluke.
 

Roverman2010

Well-known member
Like these, use loctite on the sides.
 

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Roverman2010

Well-known member
If this should happen again you will be best to drill and tap the block and place a retainer across the plug.

Have to do this mod on Jag 6 engines often. Picture for reference. Just hope replacing with a new plug with lots of loctite will work.
 

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RDavisinVA

Technical Excellence Contributor
Just get one of those rubber expandable repair plugs.
Fit it tighten the nut on the stud sticking out, fill the cooling system and drive.
No way to know why it came out.
My guess it froze at some point and fell out later or was over tapped in to a point where it went concave and didn't have enough tension to hold it in place.
 
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