How much water pressure in block ahead of thermostat?

[AlanCasida]

OK this is kind of a long story so bear with me. Since I have kind of retired my Galaxie from race duty I decided to hook the heat and a/c back up. While on a drive the heater hose had come off the heater control valve and the motor got really hot. Upon inspection I found trails on the sides of the block where coolant had escaped past the head gasket. So I did a compression check and all the cylinders checked ok but as a precaution I pulled the heads to look at them. Using a straight edge and feeler I saw there was just a minor gap(maybe .005) in the surface but after conferring with a friend I put it back together as is. I got it all back together only this time I had the heater hoses backwards from before and the output hose coming out of the intake went to the heater core first. I went for about a 6 mile drive and on the way back home I stood on it pretty good and all of sudden a bunch of coolant started running into the floorboard. Again I got the car pretty hot getting home. It was a leaking heater core. When I pulled it I found that it was all bulged out and one of the tubes had split. It was not rotted. I had the heat turned off so it was dead headed. I replaced it but before I hooked it up I wanted to see what kind of pressure I was getting inside the motor. So I hooked up an electric oil pressure gauge dead headed in the water port on the intake and a mech water pressure gauge on the extra port on the t-stat. With it fast idling at about 2000 rpm in the shop it had about 25-30 psi in the block with the t-stat closed. When the t-stat finally opened it dropped down to near zero. I went for a short drive and when I ran the motor up to maybe 3500 rpm while driving the psi in the block went to near 50 psi. When I got back home I was revving it up in the shop and the gauge after the t-stat was reading around 10 psi and in the block it would go up to around 30. I guess what I am trying to find out is that normal? I have never checked anything like this before. I think the restriction in the t-stat might cause some pressure differential but I have no idea how much. I think if I put the coolant line coming out of the intake on the heater control valve first would help to keep the core from getting too much pressure too. But I am also wondering if I might have warped the heads when I got it hot and that is causing the extra pressure. The first time I got it REALLY hot.  I just don't want to blow a freeze plug out. Any input on this would be greatly appreciated and sorry for the really long post.   

[pbf777]

............. what I am trying to find out is that normal?

 Yes, this is another function of the variable drive rate mechanical pump; which by the way is not replicated with the substitute electric pumps, and is why these (electric) should not be used in anything but 'short-duration' run engines (e.g. drag cars).   

 Oh, and .005" in the length of warpage, of these heads, is pretty much the limit (still not advisable) to ignore.   

 Scott.

[AlanCasida]

I think I’ll put my gauge on my 66 f100 and do a comparison. I may be just chasing my tail.

[2ndgear]

Alan I had the same problem that my heater core would leak after replacing it.
What I found my problem was that the fitting coming out of the intake manifold
was the wrong one. The fitting is a special one that has a stand pipe on it. If you
dont have the correct fitting there will be to much water pressure to the heater core
which will cause the core to leak. Hope this helps.

[shady]

sounds to me like the heater core was frozen up at one time and reversing the hoses pushed it over the edge.

[My427stang]

Although ballooning could of course come from freezing, I have seen the wrong fitting blow a heater core, and now if I install an aftermarket or brass fitting I modify it with a standpipe.

Ford felt they were needed and I believe it's either the creation of steam pockets that can't purge until the heat is run, or the flow amount when the thermostat is closed (which seems less likely)

I have never put a gauge on one, but I do agree your numbers sound high.  If you are running an aftermarket fitting, for giggles,  just epoxy a stand pipe with the proper OD right into the fitting and have it almost touch the floor, it won't help the total pressure but can keep it in water, not air, during filling and opening of the stat and cant hurt.  Additionally, you can drill a 1/16 hole in the thermostat to allow it to purge any air at start and reduce that pressure a bit.  I have gone up to 1/8 without any negative thermostat operation, and I have seen much more, but huge holes aren't needed in my experience

[MeanGene]

in '77 with my first 427, in my 69 Mach1, first time I nailed it hard, went to 7300 and then the windshield fogged up and the stink from antifreeze, blew the heater core. I have been using a 6" piece of copper tubing as a restrictor in the line to the heater ever since, no more problems

[Rory428]

When I first put my 59 on the road with the fresh 428, the first time I wound it out, the heater core puked all over the floorboards. (Luckily I didn`t have the new carpet in yet!). Having no idea if it was still the original 60+ year old core, or not, I had a new heater core made, and have had no issue since. I have the curved 428CJ reproduction intake manifold heater fitting, which has a crimped standpipe in the bottom.
Alan, do you have the stock type short bypass hose between the water pump and the front of the intake manifold? If so, I always thought that hose would prevent any excess cooling system pressure from building, and that any pressure above the radiator cap rating, would release past the rad cap.

[FrozenMerc]

Alan,
    What you are seeing for pressure is normal in my experience.  I built a water pump dyno at my last job for developing water pumps on small engines (generally less than 1200 cc).  The dyno had an electric motor that drove the pump, and then there was a mock cooling system with a throttling valve in place of the thermostat in order to control head pressure at the pump.  With the throttling valve nearly closed, and flow restricted to just a trickle, it was not uncommon to see steady head pressures of 50 to 75 psi, depending on the pump specs.  Add in the water hammer effect from a rapidly closing thermostat due to a rapid cool down (think about splashing through a deep puddle), and it was easy to see coolant pressures spikes exceed a few hundred psi between the pump and thermostat.  I have seen situations were the impeller would actually be knocked off the shaft.

[AlanCasida]

I just put my gauge on my '67 F250 w/390 and I got similar readings. At 70 mph around 3000 rpm I was getting around 47 psi. However, when I shut the truck off my gauge maintained about 22 psi. The pressure should have equalized with the radiator by then and been lower than the rating of the cap. What this tells me is using an oil pressure gauge might have been the ideal thing to use. What it also tells me is I got similar readings from a known good source so I am probably good. Much to do about nothing! I do have the intake bypass hose hooked up but the heater hose fitting is not restricted. I am going to either get a restricted fitting or make a restrictor for what I have. Plus I will make sure I have the pressure hose going to the heater control valve first so it doesn't deadhead in the heater core.
Thanks for all the input, I really appreciate it.

[pbf777]

................ so I am probably good. Much to do about nothing!

     Yep!

     But, realize that for yourself and others who may have been unknowing of such, the education, as always, is invaluable.   

     Scott.

     

[jayb]

Somewhere in the Ford SOHC manual or documentation is a statement that at high RPM, water jacket pressures exceeded 90 psi.  So I don't think what you are seeing is unusual, Alan.

Also, I take exception to the comment that electric water pumps are not suitable for the street.  I've been running them on my race cars at Drag Week, and in my daily summer driver, for years.  In fact, the constant flow provided by the electric pump is a big advantage, in my opinion.  With an electric pump on your engine, Alan, I don't think you would ever have experienced the problem that you did.

[Cyclone03]

Although ballooning could of course come from freezing, I have seen the wrong fitting blow a heater core, and now if I install an aftermarket or brass fitting I modify it with a standpipe.

Ford felt they were needed and I believe it's either the creation of steam pockets that can't purge until the heat is run, or the flow amount when the thermostat is closed (which seems less likely)

I have never put a gauge on one, but I do agree your numbers sound high.  If you are running an aftermarket fitting, for giggles,  just epoxy a stand pipe with the proper OD right into the fitting and have it almost touch the floor, it won't help the total pressure but can keep it in water, not air, during filling and opening of the stat and cant hurt.  Additionally, you can drill a 1/16 hole in the thermostat to allow it to purge any air at start and reduce that pressure a bit.  I have gone up to 1/8 without any negative thermostat operation, and I have seen much more, but huge holes aren't needed in my experience

I thought I was the only one who does this. I use 1/8” pipe nipples cut to length about 1/2” off the intake floor. I just thread the heater hose fitting 3 or 4 full threads.

[CDXXVII]

Plus I will make sure I have the pressure hose going to the heater control valve first so it doesn't deadhead in the heater core.
Thanks for all the input, I really appreciate it.

My unmodified Galaxie has no heater control valve in the line going to/from the heater core. The flow is on even with the heater off.

[AlanCasida]

Plus I will make sure I have the pressure hose going to the heater control valve first so it doesn't deadhead in the heater core.
Thanks for all the input, I really appreciate it.

My unmodified Galaxie has no heater control valve in the line going to/from the heater core. The flow is on even with the heater off.

What year is your car? My '66 Galaxie factory a/c car came with one.