Ive had my 95 for about 18 mos and put 20K on it or so. We recently came back from a 1500mi or so trip and a couple weeks prior I topped the coolant overflow bottle to exactly the full line when cold. I checked it several times and saw it vary in level,but always lower a little. I have noticed this for the duration of ownership of this truck and also a similar issue with my 93 I had. Today I pooped the hood and the coolant bottle is about 3" below the full line. I have checked this thing high and low for leaks, I cant imaging the ambient temp (32 this am) would make it contract. I have also mentioned a miss after it warms up that is sometimes worst than other times. Ive never heated it up, but I dont know its history. If I had a headgasket leak and it was putting out the fire so to speak with the coolant leaking into a cylinder then wouldent combustion pressures enter the radiator also and cause the obvious? If I do a cooling sys pressure test should there be "0" drop and how long should it hold?
What other tests can I do??
Thanks everyone.
Scott.

 

Buy or what ever a pressure tester and pump up to 20lbs then with the fuel shut off and the turbo disconected from the exhaust manifold turn eng. over and look for coolant in the exhaust man. also look every where els for leaks , how much coolant in how many miles, get an oil analisis, a few thing to check.

 

The best way to look for an internal leak is to have an oil analysis performed. That will let you know if you have coolant in the oil. Then, if that turns up positive you will need to check the oil cooler for perforations, and the head for exaust seat cracks that have opened into the cooling passages or for a leaking headgasket.

The most common way these guys loose coolant from a sound engine is through the compression seal located on the thermostat block (above the alternator on the side of the engine), through the sealing surfaces of the heater core, or out the freeze plug at the back of the engine. However, you may want to inspect the waterpump weep hole and see if you have any staining from a leaky seal.

I do not favor the radiator pressure checks for much other than checking for bad hoses or a bum radiator core. You can accomplish the same thing by getting the engine up to operating temperature and then using a very strong light and inspecting the engine. Internal leaks are best detected using either a compression test or oil analysis.

Generally speaking if the coolant is leaking as slow as you say, you can add a jar of Barr's Leak and stop further leaking, sometimes for years and years.

 

When my headgasket south it was leaking on the passenger side of the block but it never made it to the ground. It just evaporated on the side of the block undneith the manifold.

 

Quantity I`ll say 12 oz`s in 2k miles. Ive looked all over the engine,bellhousing and havent seen anything yet. Ill have the oil tested its due soon for a change. About the "compression seal" on the thermostat block? you mean the gasket. Been awile since I swapped thermos in a 12v but I recall a O ring seal?? only around the thermo itsself. This was a Cummins part.

 

Are you seeing any oil & water mixing ?[rad., crankcase, trans.fluid] the last issue of TDR had an artical about the trans. cooler on the ft. pass. side of the eng. leaking .

 

Nada, I even scriutinize the oil after draning it for a change. It is a stick so no T cooler. No ugly stuff in the overflow bottle either. this Im aware of after a 2.8 chevy with the intake mani problems. I serviced the radiator also 15K ago and it all looked good. If I remember rightl on my 93`s the heat exchanger on the passanger side of the block below the head?? I dont seem to see one on my 95, or am I just looking in the wrong place?

 

If your not getting any fluids mixing this most likly isn't it , but what the artical was refering to is a cast iron part that covers most of the ft. of the block on the passanger side.

 

Apache, my exchanger is on the passenger side below the exhaust manifold.

 

I just finished replacing my head due to numerous cracks in the exhaust seats. I had noticed a slight loss of coolant level over an extended period of time. The last time I towed the water level was low and the engine overheated before I could get it pulled over on the mountain. This put it over the edge and it started blowing water out the overfill on a hard pull. On flat ground it wouldn't push the water out. I had over 20 cracks in the head.

I believe the oil analysis is the best bet for you.

Do you pull a heavy trailer? Maybe the water is being lost mainly when you pull.

 

Could be you have the dreaded "53" block and its leaking just above and behind the tranny heat exchanger!

 

Maybe I have gone brain dead but I dont see any heat exchanger. I remember the one on my 93 looked like a block heater big as day under the manifold.
In regards to when I loose it, this trip we were hauling a camper but it never got hot or even warm enough to make the temp stabilize, it still has the constant swinging temp guage. The only time this stops is in summer at 90+ degrees pulling the cuesta grade with 5K worth of trailer.
Ill check again for the heat exchanger tomorrow when its light.

 

The heat exchanger is under the exhaust manifold. Your best bet is to get a mirror so you can look up under the exhaust manifold.