XR4 - Water pressure

I have a mercury XR4 which shows very little water pressure. 0-2 psi at idle and maybe 6-8 PSI at WOT. I've installed a new water pump (complete) replaced the thermostats, replace the poppet valve (complete) and still get exactly the same results.

When I'm running in warm water the temp gauge goes way up, especially if I'm running at less than about 1/3 throttle. Last summer the buzzer went off a couple times when I was running slow in rough water and I had to shut it down to cool. In the cooler winter water (50-70 deg.) it doesn't get quite as hot.

One time last summer I revved it up hard in neutral and the pressure jumped up to 8-10psi at idle and 18+ at WOT. This only lasted for one day and it went back to the same thing it always does the next time I put it in the water.

I've checked all the rubber water tubes which appear to be clear. I can take out the thermostats and I get a good flow through both sides and to the pee hole, but just not much pressure. I even took off the tube at the top of the block (that feeds the pressure gauge and the poppet) I put on a piece of spare tubing just to see the flow, and it seems to again flow well, but just has very little pressure (at idle).

This motor has had the lower unit replaced with the larger diameter version. My theory is the water pump is not sealing properly to the water tube. Perhaps due to a mis-matched lower unit (shouldn't all Mercury V-6 L/U be interchangeable?) Anyone have any thoughts on this? Is it possible to somehow put in an extra seal under the water tube to make sure this is mating up properly?

Also - I believe I used Sierra kit #18-3319. Is there a possibility this isn't the correct kit for this particular lower unit? If so, is there any way to identify the lower unit and know which pump I need to use to make this work properly? Sierra also makes pump models #18-3314 and #18-3319 for the Mercury 150. Could one of these actually be the correct model for this lower unit/powerhead combination?

I see lots of other XR4 owners with a similar issue - Is it possible this is happening anytime a replacement L/U is put on an XR4?

Thanks for any help.

Duke
Smyrna, TN

Re: XR4 - Water pressure

There's many possibilities.

1. Did you replace the entire water pump, including the plate under it? That is often the source of poor performance.

2. The water tube going up to the power head could be damaged, kinked, or loose at either end, allowing water to leak out and lose pressure.

3. The poppit valve may have some debris in it, or the grommet/seat thingie might be loose, or the spring might be broken or weak. Normally it holds water in the block till it hits about 12 psi, then allows it to dump.

4. You can take the thermostats out and heat them up in a pan of water to see when they begin to open. Should be about 140 degrees if I remember right. I don't know how they do it, but I've seen the gaskets all fuddleduddled up when tstats were installed.

Once I ran full tilt into shallow water filled with a stringy algae. I paddled back and basically had to replace the pump and clean out thermostats, poppit valve, and everything under the exhaust cover to get it to cool again.

Based on your combination of symptoms, I'd bet on #1 or #2.

One more thing, there is a high pressure and a low pressure version of this system. The pumps are different diameters and the parts don't interchange. Does the new pump look like the old one? The XR4 is a high pressure pump, and I don't think you'd get enough flow through it with a LP pump to cool it. It's a pretty hot (burns lots of fuel) motor to start with.

hope it helps
John

Re: XR4 - Water pressure

John, thanks so much for your help - Replies below.

1. Did you replace the entire water pump, including the plate under it? That is often the source of poor performance.

Yes - I replaced the entire pump, including the plate.

2. The water tube going up to the power head could be damaged, kinked, or loose at either end, allowing water to leak out and lose pressure.

That's what I'm thinking - I did look up through the tube and it was clear, and it's not loose, but I'm not sure it's sealing properly to the top of the water pump since you can't see it when the lower unit is installed.

3. The poppit valve may have some debris in it, or the grommet/seat thingie might be loose, or the spring might be broken or weak. Normally it holds water in the block till it hits about 12 psi, then allows it to dump.

I've installed a brand new poppit valve, including the spring.

4. You can take the thermostats out and heat them up in a pan of water to see when they begin to open. Should be about 140 degrees if I remember right. I don't know how they do it, but I've seen the gaskets all fuddleduddled up when tstats were installed.

Brand new thermostats. Even with both T-stats removed there's very little pressure.

Once I ran full tilt into shallow water filled with a stringy algae. I paddled back and basically had to replace the pump and clean out thermostats, poppit valve, and everything under the exhaust cover to get it to cool again.

What do you mean by 'under the exaust cover'. Is that the same area that houses the drive shaft and water tube?

Based on your combination of symptoms, I'd bet on #1 or #2.

On #2 how can I be sure the tube is fitting correctly to the pump, and not losing pressure right there?

One more thing, there is a high pressure and a low pressure version of this system. The pumps are different diameters and the parts don't interchange. Does the new pump look like the old one? The XR4 is a high pressure pump, and I don't think you'd get enough flow through it with a LP pump to cool it. It's a pretty hot (burns lots of fuel) motor to start with.

The pump I replaced looks exactly like the old pump, but that was on the [big] L/U that came with the motor (I got it used), so I don't really know if it's a HP or LP pump. So what you're saying is that the motor is looking for a HP pump, and the L/U that's installed might have a LP pump? I'm pretty sure I installed the Sierra kit #18-3319, which is the same one that went on the original XR4 L/U. Is kit #18-3314 or #18-3319 a HP or LP pump?

hope it helps
John

Re: XR4 - Water pressure

Sounds like there may be some broken old impellar parts still in the system. Pull thermostats and pop it valve. Run and look for debree out of head.

Re: XR4 - Water pressure

You can't expect any water pressure with the thermostats and popet valve removed because water has a straight shot through the engine. Get the serial number off the engine, and then go to the Mercury Marine web site. Click on Parts Express and enter your serial number to view the parts list for the engine. That will get you the part number for the standard lower unit. If they list the other lower unit, and the one you have happens to be the same year, you should find that part number as well. If you have no idea what year the new lower unit is you have some research to do.

Re: XR4 - Water pressure

Thanks Silvertip.

I understand regarding removal of T-stats and low pressure. But what about if the T-stats are installed and I'm looking at the pressure out of the bypass tube at the top of the block?

My pressure gauge is installed with a Tee on this bypass tube. Same as in this description. Am I looking at the correct pressure?

'http://www.diy-boat.com/index.php?option=com_content&task=view&id=151&Itemid=49[/url]

-Duke

Re: XR4 - Water pressure

I'm not familiar with the plumbing on that engine but here's what I would try. Cap off the connection you have now. Install a "T" in the tell tale line and connect the gauge there and see what you have. You can again refer to the picture I posted earlier. If you still don't have any water pressure to speak of, pinch off the tell tale after the "T". If pressure still eludes you, I think you have a problem either with the pump (impeller key not installed), the water tube is misaligned or the gasket is plugging the tube, there are remnants of the original impeller lodged in the tube or you installed the thermostats and/or popet valve incorrectly. This is a process of elimination so start by dropping the lower unit. Set it in a large tub of water and figure out a way to run the drive shaft (for example with a large electric drill). Just make sure you don't bugger up the splines. If the pump is good you should end up with a bath. Carefully examine the water tube to make sure its clear and the gasket is in place. Most engines with a good impeller will idle in the 5 - 8 PSI range and run at 15 - 17 PSI at WOT. Obviously not all engines are the same but those numbers are at least in the ball park. I'm really wondering if you failed to get the impeller drive key in place properly and the drive shaft is just spinning in the impeller but still turning it a little.

Re: XR4 - Water pressure

Man, what a mess of information, and misinformation.

The exhaust cover is on the back of the engine, under the clamshell hinges and coils. It has a gazillion bolts in it, and is in several layers, a cover, and an exhaust divider, and several gaskets and seals. Taken off, you can see into a lot of water jacket, and see if small passages are getting clogged. You also get a pretty good peek at the exhaust side of the pistons. It's a project to get it off, and you could break bolts, which is a headache.

The water tube slips into a rubber grommet thingie on the water pump. It should slip in easily, but definitely not be sloppy loose.

Sounds like the pump should be fine.

IMPORTANT----WATER PRESSURE GAUGE HOOK UP
______________________________

On the top of the block, behind the flywheel, there is a threaded hole. The only thing in that hole should be a barbed adapter for the water pressure gauge. If there is another hose going somewhere, it is bleeding off pressure. I have an XR4 in top shape. I could take pictures if you wish.

The lines from the thermostat housings to the telltale fitting only have water in them that has gone through the thermostats. That is NOT the place to hook up a presssure gauge. In fact, it is normal for the engine to not pee until it is pretty well warmed up.

I suspect the pressure gauge is mis installed, and the pressure is actually high. The problem, as another has stated, might be chunks of debris stuck in water passages.

I'm really curious about where the "bypass" hose goes. My XR4 is 1988, a 2.4L block. There is a pressure passage that modifies how the poppit valve operates, but it is internal in the base plate.

normal pressure is almost none at idle, but perceivable and it pees if warm. It goes up to 'bout 12 at 3000 rpm, steps back a little, then ramps back up to 15 or so at WOT. It varies some as parts wear or I hit a little crap in the water.

If you need further help, some clues to the exact motor would help. Year, Serial Number, Carb numbers, and maybe even pictures.

hope it helps
John

Re: XR4 - Water pressure

John, I agree with you 100%. That is the way it should be plumbed in and the pressures will about what you said. My OEM for my 89 200 hp says 12 psi at wot.

Re: XR4 - Water pressure

It's a 1990 XR4 2.4L, ser# OC218772

How would I know if the water tube fits sloppy or loose when I can't see it mating up to the water pump when the L/U is slid on? Also - is there supposed to be any sort of O-Ring between the water tube and the guide tube, or does the seal/gasket on the water pump completely take care of the seal?

The pressure gauge is teed off of the bypass tube going from the top of the block just behind the flywheel to the rear of the poppet cover on the starboard side of the motor. It's the same installation as the one pictured here;

'http://www.diy-boat.com/index.php?option=com_content&task=view&id=151&Itemid=49[/url]

When I removed the bypass hose from the upper fitting and ran the motor on the muffs, there was lots of volume of water coming out, but not much pressure. I could easily stop the flow just by putting my finger over the hole (I used a short piece of tubing so I didn't get the motor wet).

Is the exhaust cover below the reg./rect. (which is the rear cover of the water jacket between the heads on the XR4)?

It's also been suggested I may have a head gasket problem. Is it possible for a head gasket to cause low water pressure at all RPM?

Lastly - I've considered the possibility the woodruff key on the impeller is slipping. However if this was the case, I wouldn't think I'd get any pressure at all...

Thanks so much for helping me get this figured out.

-Duke

Re: XR4 - Water pressure

The guide tube is just that, a guide. It could be discarded without consequence. There is a lipped seal in the top of the water pump that the tube slips into. If it looks good, it probably is. If it's folded up goofy or torn, it isn't. A fresh one should have come with the impeller. Usually if this is bad, you'll have water coming out of shaft holes and such in the mid where it isn't supposed to be.

The impeller is driven by a flat on the shaft and a loose drive pin of some kind that just sits there. Either it works or it don't. There's no slip to it.

You found the exhaust cover. The exhaust ports are on the inside of the V, and dump into the central chest where they are then routed downward to the tuner in the mid.

Your poppit and mine are exactly the same with the exception of the cover and the tube to the top. There should be no flow through that tube, just pressure. It modifies the operation of the poppit valve. If you disconect it and water then flows out of the poppit valve, the diaphragm is bad. (Could be the problem) Fuel hose is listed on the parts list for the hose. (5/16 in diameter or so.) Theoretically you should be able to plug it off with no consequence. It is supposedly an improvement of the old one. It should increase water pressure slightly.

A couple of pounds of water pressure is pretty easy to hold back with your thumb on a hose that small. Sounds normal.

It is possible for a head gasket to cause overheating. There are many small, like 3/8 inch water passages that can get plugged. The worst mess is when you cut an old rotten floating log in half while on plane, and the wood splinters get caught in all those little holes. Usually that causes pressure to go up.

Latest thought. Have you checked the gauge for correct reading. They are pretty cheeeeeep gauges, and are known for "drifting".

You can view exploded view parts drawings at mercruiserparts.com Go to parts by pictures, outboards, mercury/mariner, XR4, serial range.

mercurypartsexpress has the engine lookup disabled while they try to figure out how to really mess it up. It used to be the best on the web.

hope it helps
John

Re: XR4 - Water pressure

If Mercury is down, go to Doug Russel.com. Pretty much the saem. They are sometimes a few bucks cheaper on some things. I use them because they ship to your address where Mercury wants you to pick up at a dealer.

Re: XR4 - Water pressure

Thanks, but that's dougrussell.com (double L) 'bout the same parts diagrams as mercruiserparts.com

Mercury parts express works through local distributors. The shipping is up to the distributor. I don't have any trouble with that. I just have to call them sometimes and tell them to look at the computer once in awhile.

John

Re: XR4 - Water pressure

One more thought for Duke.
These engines burn so much fuel that it's pretty easy for fuel mix or timing issues to manifest as overheating issues. Just a thought.

John

Re: XR4 - Water pressure

j_martin said:

One more thought for Duke.
These engines burn so much fuel that it's pretty easy for fuel mix or timing issues to manifest as overheating issues. Just a thought.

John

Click to expand...

I've got to get the pressure issue fixed first.

One other thing, when I start it on the muffs there's a ton of water coming through the propeller hub, despite not much water pressure in the cylinder block. Does that mean anything to you?

Also - What about the seal at the top of the water tube? Can it go bad - Any way to check it?

Here's my to do list;

1. Install a new water pressure gauge and supply tube.

2. Pull the lower unit and re-inspect the pump - Making sure the rubber seal is in place, and making sure the flaps on the impeller are aiming the correct direction, and that the woodruff key is in place.

3. Measure the length of the water tube in relation to the top of the water pump and determine whether they are mating up correctly.

4. Pull the heads and check the gaskets and look for any debris blocking the water jackets.

5. Pull the exhaust plate and look for anything blocking the water flow.

6. Pull the poppet cover and start the motor to see if any debris comes out.

Am I missing anything?

Re: XR4 - Water pressure

Take it easy. Check it out after you replace the pressure gauge and before you go wrenching on everything.

Low pressure at idle is pretty normal. As long as water is coming out the prop hub, and it pees a little after it warms up enough to open up the thermostats.
Normal operation is fairly low at idle, slowly ramps up till the poppit opens up, usually about 3000 rpm, and 10 psi or so, drops back a little, and ramps back up to at least 12 at WOT. Way high at WOT indicates a blockage.

I don't know if it's been asked yet, but is your motor deep enough in the lake to cover the water intakes while on plane? Is there a chance that it's sucking air? The XR4 should pull fine almost surfacing, but the 4 1/2 inch gearcase might not.

If you still don't get much pressure at WOT, there must be some other way water is escaping the cooling system, or air is getting into the suction side of the water pump.

To be real honest, your set of symptoms all seem to point to a stuck open poppit valve. Maybe mis-assembled or missing something.

I'll ask the oldtimers over on scream and fly.

hope it helps
John

Re: XR4 - Water pressure

Why a new gauge. Remove it, head to your local gas station. Have them set their regulator to 15 PSI and using a nozzle, put pressure on the gauge. It should read 15PSI or thereabouts. Make sure the tube is clear. I also feel you have poppet valve issue or the problem is in the water pump area. Don't be pulling the engine apart until you've confirmed those items are correct.

Re: XR4 - Water pressure

Thanks for the idea on the pressure guage. I've got a compressor with a regulator here at work. Can I buy new tubing by itself? It might be smart to make sure I have a fresh/clear supply tube if the gauge is showing good.

As for the water intake - The upper 2 intake holes are plugged [by the previous owner]. I've lowered the motor as deep as 8" below the pad [propshaft] and it does exactly the same thing. I'm running about 3 1/2" below pad right now. Sucking air at speed would also not explain why I'm showing barely over 0 PSI even when fast idling out of the no-wake zone and the temp needle shows hot after only 4 or 5 minutes if I don't get on plane. (I do know the buzzer goes off when the temp needle gets all the way to Hot).

Is there a way to test the poppet theory? Maybe the old one was in there wrong and so I put the new one in wrong too? From what I remember I put the new one in exactly like it's shown here (except my poppet cover runs horizontal - the one in this diagram is vertical?) Can I take the poppet cover off and just hold the poppet in place by hand to make sure it's sealing?

'http://www.crowleymarine.com/mercury_parts/555/140.cfm[/url]

Let me know that the guys at Scream and Fly say - Or I can just post the question there myself. Which forum should I use?

Really appreciate you guys' help!

-Duke

Re: XR4 - Water pressure

Could it be possible there's too much restriction on the suction side?

screamandfly.com forums tech talk.

see ya there

Re: XR4 - Water pressure

I know about how the poppit goes together and feels. It's hard to put into words.
One common fault is the grommet in the bottom of the hole gets loose, and fails to seal, or cocks and jams the valve open.

Could it be possible there's too much restriction on the suction side?

screamandfly.com forums tech talk.

see ya there

John