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Discussion Starter #1
New rebuild is pushing coolant out of tne fill neck and builds pressure when cold. I dont appear to be leaking coolant into a cylinder, and i dont have any bubbles in tne radiator when shop air applied to each cylinder using a compression adapter.

My queztion is would this most likely be head gaskets or something bigger? I am really confused as i dont appear to leak coolant on the engine just have what i assume to be compression gas in the coolant.
 

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You said it was freshly rebuilt, have you run it long enough to warm up? The coolant expands as it heats up, so don't fill it quite so full and then run it with the cap on until it gets to operating temp, and the overflow has gone into the recovery bottle. I haven't had one yet that didn't push a little out right at first. If it is building pressure, is it so much that it trips the pressure relief on the cap? Or is it just sending excess coolant to the recovery bottle?
 

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Discussion Starter #3
Yes, it has been hot and has pushed coolant the whole time. It will build enough pressure cold to make the hoses rock hard and push coolant around the cap (not to puke tank). If you run it cold with the cap off with in one minute it will be flowing coolant out the fill neck at a good rate. But I never see any bubbles ant it doesn't overheat. I am just afraid that I will blow a rad hose going down the road! I don't have any white smoke indicating burning coolant either.

Looking for advice before I pull this motor for the 4th time since I started the rebuild!!
 

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Get a good radiator test kit. If it is getting into the raditor, it will go the other way. Doing that hot OR cold, right after a rebuild, I would think there is something with the head gaskets, or a cracked head you didn't spot, most likely in one of the exhaust ports. So when you hook up the test kit, pull the exhaust manifolds and look there for coolant running out. The reason you don't see it coming out the exhaust ot running down the cylinder might be because the pressure there at that particular spot is greater than the coolant pressure ,andthe crack "seals up" when it cools. The heat from the exhaust gasses would also evaporate anything there is to see before it becomes visible. The heat also might be expanding the crack so that it only leaks after it warms up. With exhaust you don't have to wait for the rest of the engine to warm up. If you can't find it cold, start it up, and hold a mirror in front of the exhaust ports one at a time. You might see a slightly wet spot, or see some vapor on the mirror. Good luck, it sometimes gets pretty rough finding that stuff.
 

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Did you get new injector cups with your rebuild? A cracked cup will allow the coolant system to get pressurized by fuel. Tell tale sign is a puking reservoir and coolant smelling like diesel...which could also be a cracked head, but on a fresh rebuild, I'd lean toward a cup problem.
 

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Did you get new injector cups with your rebuild? A cracked cup will allow the coolant system to get pressurized by fuel. Tell tale sign is a puking reservoir and coolant smelling like diesel...which could also be a cracked head, but on a fresh rebuild, I'd lean toward a cup problem.
IDI engines don't have injector cups.
 
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