I recently installed my water pump and thermostat housing onto a remanufactured 4.0L inline 6 engine. After weeks of operation, I noticed that the engine would periodically leak coolant. It would not always leak coolant. It would only intermittently leak. I was uncertain as to where the leak was coming from: the thermostat gasket, the water pump gasket, or the threads of the metal tubing screwed into the top of the water pump (this tubing takes warm coolant to the cabin air heat exchanger). There just was not enough visibility, with all the accessories installed, to see where the coolant was emerging from.
In response, I replaced the gasket on the thermostat housing (amply applying liquid gasket maker; so much so that it squeezed out the sides of the interface, making a small ‘muffin top’) to determine if it would stop the leaking. It did not stop the leaking. Next, I installed teflon tape onto the threads of the tube (leading to the cabin air heat exchanger) screwed into the top of the water pump (I failed to use teflon tape when I reinstalled the water pump on the remanufactured engine). Since this required the removal of the water pump (because I could not unthread the tubing with the water pump still attached to the front face of the engine) I also replaced the gasket on my water pump (using a paper gasket that had a waterproof ‘bead’ imprinted on it - I only added liquid gasket maker, sparingly, at the screw holes, since the waterproof ‘bead’ did not extend to the screw holes). After these actions, I still noticed that coolant was leaking after engine operation. (It does not appear to leak while it is at rest.) I am still unsure as to whether the coolant is leaking from the gasket of the thermostat housing, the water pump, or the threaded tubing (though I think it is much less likely that the coolant is leaking through the tubing threads, now that I have added the teflon tape).
Separately (but relatedly), a new coolant hose (the one attaching the bottom of the water pump to the bottom of the radiator) popped off the water pump during operation. The logical explanation would appear to be that the vapor pressure in the coolant loop exceeded the hold force of the hose clamp I used to affix the hose to the water pump (perhaps I under tightened this when I installed the remanufactured engine, but I am uncertain). This perplexed me as I thought that the vapor pressure in the coolant loop was limited to ~18 p.s.i. by the radiator cap (these have spring loaded relief valves designed to release fluid and gas to the radiator overflow tank when vapor pressure greater than ~18 p.s.i. is generated). I inspected the existing radiator cap and noticed that the large rubber flange, performing the hold back sealing function on the coolant loop, was slightly increased in diameter (through long periods of compression). I became concerned that the over-diameter rubber flange might be binding with the sidewall of the radiator cap receptacle, thereby intermittently preventing over pressuring from being released from the coolant loop. As a precaution I purchased a new radiator cap.
The coolant still leaks intermittently, even after the radiator cap was replaced. I began hypothesizing that perhaps my tightening of the screws, holding both the thermostat and water pump housings to the front engine face, was done to too small of a torque rating. My large torque wrench has some parallax ambiguity, leading me to believe, for example, that I have it set to 15 foot-pounds, when it may in reality only be 5 foot-pounds. According the Chilton Repair Manual for the 1987 - 2008 Jeep Wrangler, I should have torqued the thermostat housing bolts to 156 inch-pounds, and the water pump hosing bolts to 9 - 18 foot-pounds. I will likely increase the torque on both sets of these bolts and see if this stops the coolant leakage problem.
Open questions for this forum.
1) Does the intermittent nature of the leaking suggest that this is a hold back pressure issue for the thermostat housing and the water pump?
2) Should I simply increase the torque settings of the attachment bolts for both the thermostat housing and the water pump, then observe whether or not the intermittent leaking stops?
3) Is it possible that gasket installation is a far more sensitive process than I currently realize, and that I need to reinstall these gaskets following a much more rigorous protocol?
4) Should coolant gaskets be installed with liberal amounts of liquid gasket maker, or should they be installed with as little liquid gasket maker as possible?
In response, I replaced the gasket on the thermostat housing (amply applying liquid gasket maker; so much so that it squeezed out the sides of the interface, making a small ‘muffin top’) to determine if it would stop the leaking. It did not stop the leaking. Next, I installed teflon tape onto the threads of the tube (leading to the cabin air heat exchanger) screwed into the top of the water pump (I failed to use teflon tape when I reinstalled the water pump on the remanufactured engine). Since this required the removal of the water pump (because I could not unthread the tubing with the water pump still attached to the front face of the engine) I also replaced the gasket on my water pump (using a paper gasket that had a waterproof ‘bead’ imprinted on it - I only added liquid gasket maker, sparingly, at the screw holes, since the waterproof ‘bead’ did not extend to the screw holes). After these actions, I still noticed that coolant was leaking after engine operation. (It does not appear to leak while it is at rest.) I am still unsure as to whether the coolant is leaking from the gasket of the thermostat housing, the water pump, or the threaded tubing (though I think it is much less likely that the coolant is leaking through the tubing threads, now that I have added the teflon tape).
Separately (but relatedly), a new coolant hose (the one attaching the bottom of the water pump to the bottom of the radiator) popped off the water pump during operation. The logical explanation would appear to be that the vapor pressure in the coolant loop exceeded the hold force of the hose clamp I used to affix the hose to the water pump (perhaps I under tightened this when I installed the remanufactured engine, but I am uncertain). This perplexed me as I thought that the vapor pressure in the coolant loop was limited to ~18 p.s.i. by the radiator cap (these have spring loaded relief valves designed to release fluid and gas to the radiator overflow tank when vapor pressure greater than ~18 p.s.i. is generated). I inspected the existing radiator cap and noticed that the large rubber flange, performing the hold back sealing function on the coolant loop, was slightly increased in diameter (through long periods of compression). I became concerned that the over-diameter rubber flange might be binding with the sidewall of the radiator cap receptacle, thereby intermittently preventing over pressuring from being released from the coolant loop. As a precaution I purchased a new radiator cap.
The coolant still leaks intermittently, even after the radiator cap was replaced. I began hypothesizing that perhaps my tightening of the screws, holding both the thermostat and water pump housings to the front engine face, was done to too small of a torque rating. My large torque wrench has some parallax ambiguity, leading me to believe, for example, that I have it set to 15 foot-pounds, when it may in reality only be 5 foot-pounds. According the Chilton Repair Manual for the 1987 - 2008 Jeep Wrangler, I should have torqued the thermostat housing bolts to 156 inch-pounds, and the water pump hosing bolts to 9 - 18 foot-pounds. I will likely increase the torque on both sets of these bolts and see if this stops the coolant leakage problem.
Open questions for this forum.
1) Does the intermittent nature of the leaking suggest that this is a hold back pressure issue for the thermostat housing and the water pump?
2) Should I simply increase the torque settings of the attachment bolts for both the thermostat housing and the water pump, then observe whether or not the intermittent leaking stops?
3) Is it possible that gasket installation is a far more sensitive process than I currently realize, and that I need to reinstall these gaskets following a much more rigorous protocol?
4) Should coolant gaskets be installed with liberal amounts of liquid gasket maker, or should they be installed with as little liquid gasket maker as possible?
