M1008 collant leaks

[MyAngry85]

So i bought an '86 M1008 awhile back. I swapped my 1 year old heavy duty radiator and thermostat from my M1009 and put put in all new hoses. First coolant started leaking from the water pump seal found two loose bolt at bottom of pump, leak gone. Then found a leak at the upper rad hose at the thermostat, tightened hose clamp, leak gone. Now it seems I'm loosing coolant at the seam where the fins meat the tank on my practically new radiator. Kind of at a loss. Any ideas or input would be great.

On a side note polyurethane motor mounts are a terrible idea. they caused a lot of loose bolts on my 6.2, went back to the rubber.

Thanks.

 

[ralbelt]

I would take the radiator to a good rad shop and have it repaired. If its only a year old I would not want to put sealer it. Get it done right.

 

[overlordofmars]

Get a radiator pressure tester fast ! Forget the fact you have a 16 pound cap, they jam. I had one truck build up 38 pounds of pressure when at fast idle due to a leaky head gasket allowing pressure into the cooling system. Blew 2 radiators apart before I found the cause.

 

[MyAngry85]

How can I tell for sure if it's a head gasket? Is there anything else that can cause that much pressure? And if there is enough pressure to blow the radiator why wouldn't the cap be opening? Thanks guys

 

[doghead]

Does your radiator have a warranty?

A system pressure tester can be used to see if your making pressure(above what it should) as well as for leaks.

Caps can be tested too.

 

[overlordofmars]

Sometimes the radiator cap spring does not let off at the desired pressure. ( especially those Chinese crap ones ) Just five to ten pounds too much pressure can cause leaks and blow outs due to over cooling pressure. YOU also have to remember your reserve tube that that cap releases to is just usually 1/4 of an inch !!!! Get a severe head gasket leak under high rpm it can create pressure too fast for that small tube size to vent fast enough. In other words the pressure and flow would climb too fast, with too much volume under high rpm for it to escape through such a small channel. Thus under highway speed your engine coolant pressure could be over 50+ pounds ! I used to put a coolant pressure tester in place of the cap and run the engine at high rpm, watch the gauge and see of I had a compression to coolant leak under high engine rpm..

It does sometimes happen. I have over 20 years working on the 6.2 it can be a beast!

 

[MyAngry85]

Ah now that makes alot of sense! Thought I got a real find, truck only has 37,000 miles and a rebuilt engine stamped '91. I guess my next step would be a comp test? Or is a coolant pressure test a better route?

 

[biggestc69]

Napa sells a kit that will check and see if hydrocarbons are getting into your coolant. I had one radiator start leaking on me. Bought a new one and a week later it started leaking. Cap tested good so I was worried about a shot headgasket. Went to Napa and bought the kit (I dont have a part # right now but I can get ya one if ya need it) and tested it. It came back negative so I took the new leaking radiator back to the shop I purchased it from. Lucky for me it was a bad crimp on the plastic tank on the side. Been going about 4 months now leak free.......knock on wood.

 

[biggestc69]

Napa part 700-1006. Combustion leak test kit

 

[MyAngry85]

So I finally got to work on the M1008 today. Did a compression test, all cylinders checked out except for the rear on each bank. Pass side rear was 350 psi and drive rear was 310 psi. All other cylinders read between 400 and 450psi. Can i assume my head gaskets are good?