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Cucv coolant leak at rear of block

CBrinker

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One of my cucvs has a coolant leak that seems to be from the rear of the motor. I can’t really see exactly where it is coming from so I thought I would check here to get some ideas of what it could be. It seems to run down and onto the leaf spring sometimes and sometimes it runs down on the bell housing. It is a steady leak and leaves a massive puddle on the concrete under it. Thanks
 

cucvrus

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First place i would look is the coolant crosover manifold port gaskets. It has 2 up front on the coolant manifold and 2 in the rear. Left side has a coolant temperature sensor and the right side has a cover plate. They are notorious for leaking. Next would be the freeze out/expansion plugs. They are mild steel and at this point in time acidic coolant could have eaten its way thru. If one is bad they should all be changed. Brass ones will last longer and seem to me to be easier to install. I hope it is not the rear freeze/expansion plugs. But they are replaceable also. Good Luck. Report back.
 

CBrinker

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It is a coolant leak. I will check those things later this week if I have a chance, it definitely seems to be coming off the back of the motor more than the side, but you never know. Thanks
 

cucvrus

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DSCF6119.jpgDSCF6118.jpgI went and looked at a few scrap 6.2 engines I have stored. 3 freeze plugs on each side of the block. No plugs behind the bell housing. There are some small ones in the heads that can leak. Report back once you make the discovery of what is leaking. Fluid can be deceiving. It can travel and drip far from the point of origin. Good Luck.
 

CBrinker

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I finally had a chance to crawl under it and look closer at the leak. All I can tell is that it is dripping off the starter. I don’t see any coolant coming from the back heads and from what I can see there is nothing wet above the starter, so is there a freeze plug behind the starter or a common leaking point that would run off the starter?
 

richingalveston

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freeze plugs are beside the starter not above. it is either a small freeze plug in the heads or the head gasket. I think all the small freeze plugs in the heads are on the ends so it is most likely a head gasket. you can leak fluid but not have a blown head gasket at the cylinder. this is normally caused by corrosion. If the large freeze plugs are leaking then they have to be spraying some to reach the starter or they just drip down to the oil pan and do not reach the starter.
you can rent a pressure testing kit from the local auto parts store, remove the starter and pressure up the system through the radiator to find your leak.
 

cucvmule

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Hello, not knowing history of truck this may be a little long and comprehensive. I have to ask but have you checked hoses at all connections, water will travel from anywhere, everywhere. Heater hoses, clamps tight, check, affirm. Heater hoses, heatercore. The new heater cores are so cheap that a little pressure and leaks become streams.

cucvrus has givin good advise about the rear cylinder head coolant plates, they corrode, leak at the bolts, and loosen from heat cycles. Check and affirm that the bolts are snug, tight. I use coppercoat, or Teflon paste on the bolt or stud threads and silicone around bolts going through the hole to keep from leaking.

Wipe down engine as much as possible at the rear and it may take many times to look at before you can localize and pin down the leak. Day or night, flashlight, real bright light so that you can see everything. You may even take off hood to get a better view from topside. Put heavy towels or rags, or small squares of plywood at the hood corners to keep from cracking glass. You may be the best at removal but it isn't worth the chance.

Do you check antifreeze for concentration? Was the antifreeze good for the lowest freeze point in your area, and below? I ask because one 6.2 that I replaced the owner could not find leak and I took off starter and block had horizontal crack between freeze plugs. Last hurrah block seal, but is it worth the chance?

I hope it is just the coolant plate or heater hose leaking at the clamp. Sometimes it is that simple.
 

CBrinker

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Berlin, Maryland
Luckily i know the history of the truck. My grandfather got it from the military about 20 years ago and did a lot of heavy towing with it, but always maintained it. Its the best running cucv i have and has almost no rust at all. I recently replaced the heater core, hoses, radiator and hoses, crossover tube gaskets and thermostat. I will go through and take the starter off, pressure test it and check the bolts on the plate. Thanks
 

CBrinker

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I checked all that stuff thinking and hoping it would be that since I had replaced it and it could have worked loose a little, but I didn’t get that lucky
 

cucvrus

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I will be fishing at Conowingo Maryland on Friday May 24th if that is near you. I can bring a pressure tester and have a look. But yes head gaskets and cracks can leak externally . ( of course) Does the leak go away with a warm engine? Just putting the information out there if I can be of any help. Good Luck.
 

CBrinker

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Berlin, Maryland
I appreciate the offer, but I’m about 3 hrs away from there. I will probably just buy a pressure tester because I know it will be needed more having 8 cucvs in addition to other vehicles. The leak actually gets worse when the truck warms up and it doesn’t leak when it’s sitting and cold unless the truck is sitting on a slope with the back lower than the front. At first it didn’t leak at all when sitting and cold no matter what kind of slope it was on, but now it does when it’s sitting on a slope like that.
 

CBrinker

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Berlin, Maryland
Well, it looks like my luck has run out lately on the trucks. The m1008 that I daily drive just started leaking coolant from what appears to be the same spot as the other truck. I haven’t had a chance to pull the starter and look at either truck yet to see exactly where the leak is, but it looks like I’ve got some repairs ahead of me. I did go through and check all the hoses and clamps on the daily driver, I had replaced them about 4 months ago and they were still all good.
 

cucvrus

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No luck with the pressure tester you will buying? That is going to be the tell all. It should be able to maintain the 14lbs?? of pressure and not leak down any. But at this point it is all a guessing game. Pressure test it. Water leaks can be very tricky. Any fluid for that part. Good Luck. Worst case scenario is an external head gasket leak.
 

CBrinker

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Berlin, Maryland
The past few weeks have been extremely busy and I haven’t had a chance to do anything at all on the trucks. I have a pressure tester ordered, but it hasn’t come in yet. I’m hoping to work on them next week or the week after, leaks definitely are usually a guessing game. Thanks
 

CBrinker

Member
Steel Soldiers Supporter
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10
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Location
Berlin, Maryland
Ended up being a head gasket on the first truck, diagnosed it but I have not had time to fix it yet. I have been busy with m151s, mules, and mighty mites lately. My daily truck ended up having a fuel leak from the injection pump when I looked closer, not coolant. Looks like I need to put other things aside and do a head gasket job and an injection pump
 
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