I have an 86 f150 with the 5.0 efi. The timing cover was cracked so I replaced it with one from a mustang because the truck had already been converted over to a serpentine belt setup when I bought the truck and was already using this setup. Since replacing I keep blowing the water pump gasket that goes between the pump and backing plate. I know how to put on water pump and have tried it with sealant and without. It appears the cooling system is building to much pressure. So my question is would a cap or thermostat cause it to build to much pressure if they are failing. The heater core and radiator are new also. I have also checked and ruled out a blown head gasket. Thanks in advance for the help.

 

A new problem appeared after some recent work in the area? That’s the place to concentrate your efforts, instead of digging deeper elsewhere.

IIRC, portions of the troublesome gasket are clamped tight by the long bolts passing through the pump and timing cover into the engine block. Make sure the female threads in the block are clean and deep enough for the bolts. If crud has built up in the holes, the bolts will bottom out. They will seem properly torqued, but don't provide the required clamping force.

Did you replace the bolts? If so, they may be slightly longer. If possible, use studs and nuts. There would be no concern about the fasteners bottoming out and losing clamping force.

I've used long taps to clean out the female threads, followed by a shot of compressed air. I was amazed how much crud was in there. A little bit of coolant had seeped in and this set up a galvanic reaction with the alloy bolt, cast iron block, and aluminum timing cover. It made quite the crusty mess in there.

 

Ford switched things around sometimes, and things can get mixed up. Some serpentine belt systems had smooth waterpump pulleys, others had grooved waterpump pulleys. The smooth ones turned backwards, the grooved ones turned the same as the old v-belt style.

That being said, it's hard for me to believe the system can build enough pressure to blow a gasket, without spewing first out of the radiator cap. The radiator cap is usually 13 psi, 16 psi at the most. So it should lift and start overflowing long before it blows a gasket somewhere. This is a unusual problem, you re going to have to keep going over it till you find the problem. Like was mentioned you are all around it, it's what you have been messing with obviously. But it's not a common problem.

 

Here's a article I found on the subject. https://www.motortrend.com/how-to/pi...p-interchange/

 

It has the smooth pulley on it and runs counter clockwise. The truck has had this setup since I bought it almost 3 years ago. Works very well and have had no problems from it until now. I will for sure check all my holes like mentioned but I feel certain I’ve cleaned them out with air between each change. I know I did before I put the TC cover back on initially. It’s not sending anything to the overflow tank at all which is why I asked if a bad cap could cause it to build to much pressure. If doesn’t seem to do it at idle. I’ve let it run for 30 min at idle. But once you start driving and rev the engine is when it seems to blow it.

 

You probably have a 13 lb cap and a 10 lb leak.

What did you use for gasket and sealer?

 

Here's my before new water pump install. As well as the gasket sealer I used. That was recommended by someone on here. Zero, leaks. I believe I only used it around the water jackets.

 

I forgot to mention another possibility. I just installed a new water pump on a remanufactured engine. The new engine came with the timing cover already installed. I swapped the hardware from the old engine to the new.

The original configuration was a maddening mix of inch and metric fasteners. Female threads in the block were inch. Any female threads in the original timing cover were metric.

I had replaced the original timing cover several years ago. Some of the through fasteners had seized to the timing cover and snapped when I replaced a failed water pump. The replacement timing cover (Dorman?) had the same metric female threads as what I believe was the original timing cover.

The timing cover that came with the remanufactured engine? It had inch female threads. Very frustrating, and I had to replace the corresponding hardware. But the hardware looked nearly identical, 10 mm versus 3/8” diameter. The difference was only about 5 thousandths of an inch. Thread pitch was very close, too.

The upshot is it’s possible to install the wrong hardware, and get several turns before the threads jam. A 10 mm fastener is slightly fatter than 3/8” and will quickly jam. But a 3/8” fastener will fit loosely in metric threads. You can easily get several turns before it jams due to the slight difference in thread pitch.

This could lead you to believe the bolt is torqued and providing the required clamping force. You could also easily damage the soft aluminum threads without realizing it, especially if using air tools.

 

What did you use for gasket and sealer?[/QUOTE]


I have tried this now with sealant and with the permatex water pump/thermostat housing sealant. I’ve tried it on both gaskets and just on the one between plate and cover. And when I used it I followed instructions and waited 24 hours to add fluid. It held maybe 20 min longer but still blew the gasket that comes between the pump and the backing plate. I’ve tried 3 separate water pumps. I have even ran a straight edge over the cover to make sure it’s not warped. It doesn’t appear to be and if it is it’s not enough to notice with the eye.

 

As far as hardware goes it’s the same hardware that’s been on it and the cover I ordered is the exact same as the one I took off. Part numbers are the same. Same brand everything.

 

I'm getting confused by "backing plate" are you talking about that plate on the backside of the water pump ?

Or the timing chain cover and water pump ?

As far as I know, that plate on the back of the water pump was/is sealed at the factory. You should not be messing with it.

 

The backing plate that come on the water pump. It’s a mustang water pump as stated in original post. They come with a backing plate that has a gasket between it and the pump. Then they have 2 small bolts that hold it on to the pump. That is the gasket that keeps blowing out. I will try and attach a picture. You can see the 2 black bolts at the bottom. It blows right beside them.

 

Sorry, but thanks for the picture. I'm new to these newer style water pumps. The OEM style I got from NAPA a few months back was for my 86 5.0EFI, which also has the backing plate, which is sealed from the factory.

I guess you have verified the sealing surface is flat with a straight edge ?

I would think if it's a paper style flat gasket that sealer I post a picture of would work fine.

Have you looked through the "related threads" below, I see someone there used Honda Bond.

 

Where is it leaking exactly? Sorry, a little late on my post.

 

Where are you getting these water pumps? Same brand and vendor? It's a troubleshooting nightmare when you get a new part bad from stock, and then a replacement (or two) from the same defective batch. Been there, done that, even got the T-shirt.

As previously mentioned, that plate is sealed to the pump housing at the manufacturer. Is that how it was supplied to you? If preassembled, that should be about the last place to spring a leak. That's what makes me wonder if you've tapped into a defective batch.