Blowing water pump bypass hoses

Bill Spain · #1 (**permalink**) 08-31-2007, 09:52 PM

I just brought home my 302 powered Cobra. It was a 95 degree day and the coolant temp was below 200 for 3 1/2 hrs, i.e. no problems. The next day I went for a short ride and when I stopped and shut off the engine, the rubber hose cap that block off the water pump connection that typically goes to the heater blew apart and dumped my coolant. I bought a new bypass hose cap and put it on. I took a 30 minute ride with the coolant temp at about 180. When I stopped the new hose cap blew apart. Tried a new one and the same thing. The temp is OK until I stop and turn off the engine, then it heat up and builds enough pressure to blow apart the hose.

Any suggestion on what to check first.

Thanks for your input.

Michael C Henry · #2 (**permalink**) 08-31-2007, 10:33 PM

That is a thermostat bypass hose. Replace it with a length of good quality hose preferably sillicone. Make sure the new hose is as long as possible to fit in the space , the metal tube ends are clean and smooth. use good hose clamps of the correct size, Do not over tighten the clamps , you can allways tighten them more later if necessary.
My brotherinlaw once had an 84 F250 that had problems from the start. Turned out that hose had a blister between the layers that affected the inside only and wasn't visable from the outside. The blister would shrink after cooling but when taken off immediately after running, was apparent and the blister had the flow blocked. Replacing that piece of hose fixed that problem.

Jac Mac · #3 (**permalink**) 08-31-2007, 11:07 PM

Assuming the T/Stat by-pass hose is fitted as normal that WILL be the HEATER fitting that has a blanking cap fitted. To avoid this happening on race engines we remove the factory pressed in hose fitting & tap the W.P. housing for a screw in plug. Most of those rubber blanking plugs do not have any braid or weave in their construction to prevent failure when hot, therefore they wont stand as much pressure as a piece of heater hose.

Jac Mac

Rick Parker · #4 (**permalink**) 08-31-2007, 11:08 PM

Bill are you blowing the curved bypass hose or the cap on the other waterpump port?

vettestr · #5 (**permalink**) 09-01-2007, 12:57 AM

I have seen pressure problems created from incorrect expansion tank installs. You said car is new to you so no history or way to know if this was a purchased problem or not.
In short one way to determine if I am right or way off base is an easy test. With a cold engine only do not try this warm or hot. If the remote expansion tank is plumbed right you can start engine without the cap on it and it should leak nothing for a moment or two. If plumbed wrong the missing cap will puke coolant as soon as you start the engine so be ready to shut it off quick. If all is correct the remote expansion tank only has pressure when coolant is heated and then to about the level of whatever cap you have.
If it pukes coolant we can then get into the plumbing. If it does not leak no sense going through the whole 9 yards.

Bill Spain · #6 (**permalink**) 09-01-2007, 04:22 AM

Jac Mac sounds like you figured out my problem. It's not the thermostat bypass hose that is blowing up but the rubber cap clamped to the lower heater fitting. The rubber cap does not look very substantial, but I never expected that it would blow if everything else was operating properly. I thought it might be the wrong radiator cap. Anyone want to suggest what I should be running for a cap? I have read everything from 12# to 16#. I also read that Stant is the best.

First thing I will do is remove the water pump and install a plug. Jac Mac from your post, I assume the pressed in fitting will come out and I can tap the hole for a 1/4" npt plug?

Vettestr I will also perform the test you recommended to see if my expansion tank is installed properly.

Thanks everyone!

Ron61 · #7 (**permalink**) 09-01-2007, 05:41 AM

I ran a 16 pound cap and never had any problem. I also had a screw in plug in the heater hose outlet as I just never trusted the rubber cap on that smooth tube.

Ron

Rick Parker · #8 (**permalink**) 09-01-2007, 10:57 AM

13# cap should be plenty unless you are running straight coolant and pushing temps above 200-210 degree temps constantly as OEM production cars are currently. Higher ratings put more stress on hoses and gaskets.

Jac Mac · #9 (**permalink**) 09-01-2007, 02:06 PM

Quote:

Originally Posted by Bill Spain

Jac Mac sounds like you figured out my problem.

First thing I will do is remove the water pump and install a plug. Jac Mac from your post, I assume the pressed in fitting will come out and I can tap the hole for a 1/4" npt plug?

Vettestr I will also perform the test you recommended to see if my expansion tank is installed properly.

Thanks everyone!

Bill,

It will be either 1/4 or possibly 3/8, some pumps have a larger pipe that is swaged down to the heater hose size. If the pump is relatively new it may help to 'nick' the ID of the tube in the pump body with an old hacksaw blade to help collapse it and aid its removal.

Vettstr is correct also in the expansion & header tank concern. I dont know what you have in this area, but if you are thinking of running a remote header tank the fitting you are about to block off would become the recovery from such a system.

Jac Mac

Bill Spain · #10 (**permalink**) 09-02-2007, 08:30 PM

Well I have the water pump off and was able to remove the lower heater hose fitting. The resulting hole is almost 3/4" so looks like I will be tapping it for a 1/2" -14 NPT plug. Having trouble buying a tap because of the Holiday.

Question: when I reinstall the new gaskets on the water pump (both sides of the backing plate) and the thermo housing, should I apply any gasket sealer or just install dry. Also bought a new Stant 180 degree thermostat. I will drill a 3/16 hole at 12 o'clock before installing.

Rick Parker · #11 (**permalink**) 09-02-2007, 10:13 PM

Drill the hole only if you are eliminating the bypass hose from the thermostat housing to the waterpump, otherwise any necessary flow will be handled by the small hose. Use some sealant sparingly.

Bill Spain · #12 (**permalink**) 09-03-2007, 06:15 AM

Rick,

I have read in other posts that the hole in the thermostat at 12 o'clock helps trapped air to get out of the system. It is not for allowing necessary flow when the thermostat is closed.

Comments anyone?

Bill Spain · #13 (**permalink**) 09-04-2007, 07:44 PM

Bought a 1/2 pipe tap today and found a 1/2 hex socket plug. Drilled, tapped and plugged the heater hose connection on the water pump. Everything back together. Took a few times of filling the system, running up to temperature and filling again to get all the air out. Everything seems to be working fine.

Thanks to everyone for the advise. Could not have done it without you.

ox_ford_guy · #14 (**permalink**) 09-23-2007, 10:11 AM

Bill.....I had a similar problem. Those rubber blanking caps are not reinforced and cannot take higher heat and pressures.

As long as the curved hose is in place (thermostat bypass hose) I agree that tapping out the pump is likely your best solution.

However, another approach is possible:

On my Cobra, I clamped a 3" long piece of reinforced heater hose on the heater fitting with a male pipe fitting (with flanged hose clamping area) and pipe threads on the end. I then plugged the pipe thread end with a female cast iron pipe cap.
Got the pieces at NAPA and home depot.

Is mostly hidden by the pump on my 351w, looks fine and has worked out well so far.

Good luck...ox_ford_guy