Water flow issue 2002 VP 8.1gi-b

[Silverbullet555]

2002 8.1gi-b
450 hours
port side manifolds run 20-30 degrees hotter than starboard. This happens if bost is level or not; in the water or on the muffs.
I know some will say this is normal, but this a new issue and when something new comes along then something changed.
Engine does not overheat. Issue is in the flow that goes to the manifolds and risers.
Problem arose 2 years ago. I was sick last year so I didn't work on it.
Compression test is fine.
Leakdown test is fine
Manifolds and risers have been checked
Oil cooler has been backflushed
Raw water pump replaced.
Used clear hose to observe water flow. Noticed water flow to port side much less than starboard. Put equal length hoses in the system and swapped sides. The low flow switches sides as does the higher temps.

To me this indicates the issue is NOT in the cooling system after the thermostat housing. It has to be somewhere upstream of that. Possibly the thermostat housing though I have visually checked it. The other possibility is that there is some kind of blockage which is simply reducing the flow and pressure enough that one side is getting starved

 

[tpenfield]

Hi James,

You probably have come to the right place to get your cooling system issues sorted out.

Is this a raw water cooled engine or closed cooling (Heat Exchanger) ?

The thermostat housing is the main junction of the hoses on that engine (right?) If so, I would take that apart and see if you can find anything clogged inside the passages within the housing.

Are you getting the temperature readings at the exhaust manifold or the riser/elbow portion of the exhaust system ? There is a single hose attached to each exhaust manifold (right?) no second hose going to the exhaust elbow as the Merc's have?

Does the engine run any hotter than it had in the past?

What temperatures are you getting at each exhaust manifold? Do you have a baseline as to what those were in the past?

What were your compression and leak test numbers exactly?

 

[Silverbullet555]

Ted, you'll recognize this from babc. Just thought I widen the net a bit.

I had a full reply written and clicked submit and of course the site was down as it seems to be so frequently. Irritating as hell.

Raw water cooled.

The thermostat housing is the main junction. The water flows in and can split between the hoses for the manifolds and a small diversion into the engine cooling system. The one that is slow flowing is 180 degrees from the inlet.

I haven't been able to find any obstructions in the housing or the outlets but it might be that the very slight corrosion is just enough to be making an impact. I am considering running a drill bit down each passage to clean them up and make the water flow easier.

I did damage the groove the o-ring that holds the thermostat sits in a while back, but that was after the temp issues started. The thermostat is held securely. However, if there is something I have overlooked I'll replace it. I did run a camera into the manifolds and they looked fine which confirms what I saw when I took them apart 2 years back. Thay combined with the hose swap result affirms it is not and obstruction on the outlet side.

I have taken temp readings at both the manifold and the riser/elbow. At the manifold and the heads. The temps are essentially equal and are in the 160 range. The engine is not overheating. The temps at the elbows are where the difference is occurring.

At the elbows, it is a 25 degree difference at idle and 1500 rpm. At idle. The good flow side sits at about 95 and the other 120. At 1500 rpm temps go up about 10 degrees. I haven't had the body on the water since end of 2016 due to illness do I don't remember the temp range after speed runs. But I do remember the hot smell which I didn't like and is what first alerted me to an issue.

I don't have baseline numbers prior to this for the temps. I probably have compression numbers from when we bought the boat, but I would have to dig into the file.

Compression
170, 175, 170, 175, 170, 175, 170, 170

Leakdown
20%, 13%, 13%, 5%, 10%, 10%, 7%, 6%

I think I answered all the questions.

Still to try.

Remove power steering cooler and try to flush it out.

Considering taking another swing and replacing all the hoses on the water intake side from the drive through the thermostat to the manifolds. Those hoses aren't cheap.

 

[tpenfield]

Yes, recognized the thread. You will find more expertise here, but not as much on the Volvo systems vs. the Mercruiser.

It would seem that the problem is the balance of the discharge flow. Overall, the flow of water is probably adequate, else you would see it in the temperature gauge.

95 degrees is about what I get at the elbows on my Mercruisers. 120 seems a bit hot. The fact that the balance problem moved when you swapped the hoses would indicate the manifolds and elbows are fine.

Is the thermostat housing heavily rusted? Maybe it lost some metal that was balancing the flow?

I would use the IR temp gun to map the temperatures throughout the cooling flow. Here is a diagram of the heat mapping that I did on my engines a couple of years ago, when I chased a 20 degree problem throughout the season. My engines are closed cooling, but the concept is the same as far as finding the area of 'heat gain'

 

[Silverbullet555]

I do wish I had a merc for several reasons. Expertise and after market availability are two of them.

I tend to think of flow balance as well those hoses are the same diameter but in the normal set up one is 12" long and one is 3 or 4 feet long of course the longer one is also the one that has to do a 180° turn. I don't know if it is heavily rusted or not as I haven't held one that is a new casting to see what could have been lost. But, it wouldn't be hard to imagine a restricting busing eroding out and breaking apart I'm going to take it off again this coming weekend and take a closer look.

 

[Silverbullet555]

Did more work on it today. Replaced the thermostat housing, ran it a little faster and swapped the hoses back and forth. The heat differential is being created at the manifold. This is 100% a water flow issue from before the thermostat housing. I backflushed everything from the raw water pulp back to the drive. All seems to be free flowing.

To test this theory, can i plumb the garden hose directly to the intake hose of the water pump? If I did that, I would be able to see how much the water splits with more volume. I'm thinking that perhaps there is something else restricting incoming volume: a collapsed hose, something in the drive, etc. I of course want to take it to the lake, but that is where this all started so I don't expect that to show me anything else.

Next up after that is to pull the drive and see if there is something going on in there or in the hoses that go from the intake up to the raw water pump.

 

[tpenfield]

Did more work on it today. . . . The heat differential is being created at the manifold. . .

Exhaust Manifold? I thought when you swapped hoses to the exhaust manifolds, the heat difference also swapped?

Got some pictures of the various parts of the cooling system.

I did have an obstruction in the outdrive on my Formula 330 that caused a 20 degree F heat differential. I didn't find it until the end of the season when I took the outdrive off.

 

[Silverbullet555]

Exhaust Manifold? I thought when you swapped hoses to the exhaust manifolds, the heat difference also swapped?

Got some pictures of the various parts of the cooling system.

I did have an obstruction in the outdrive on my Formula 330 that caused a 20 degree F heat differential. I didn't find it until the end of the season when I took the outdrive off.

Sorry. It does follow the water. I was just saying the heat differential appears in the manifolds as opposed to the heads or somewhere else.

I need to determine where the possible leak or block points are in a dp-sm drive. Based on diagrams, there are a couple o-rings in the drive and one hose. In addition to a blockage, it's always possible its pulling just a little air which is reducing the amount of water coming in. But, usually that would resolve once the drive is in the water.

I haven't had the drive off in a while. I'm a bad owner. It wouldn't hurt to get the drive off to replace all the rubber. The bellows have been done, and the associated seals, but I bet most of the other rubber is original.

 

[Silverbullet555]

So, I ran the boat with water pulling from a bucket, bypassing the drive thinking maybe there was an issue there. Same result as before.

I'm even more at loss than before.

I'm to the point of putting a gate valve into the line that is flowing well and forcing some of the water to flow to the other hose. It's like the hydrodynamic properties of the thermo housing changed and now the water is flowing only to the outlet directly across (no matter which manifold the hose is attached to).

There is a bypass in the thermo housing that allows water to flow into that system before it goes to the manifolds.

Is there any way the recirculating water system could be pushing water out a wrong place thus requiring more water and preventing the necessary pressure from building to effectively spout the water to the two manifolds?

 

[Silverbullet555]

Split, not spout in last paragraph.

 

[tpenfield]

The recirculating pump really does not push water out of the engine block. So, probably not much effect from the recirculating pump. The sea water pump displaces the water out of the block and to the manifolds.

I think at this point you could provide some restriction to the side that seems to have too much flow and see if you can balance things out. Hopefully the temperatures will be somewhat equal.

Keep an eye on the engine temperature itself to insure that the overall flow is adequate for all speed ranges.

 

[Silverbullet555]

The recirculating pump really does not push water out of the engine block. So, probably not much effect from the recirculating pump. The sea water pump displaces the water out of the block and to the manifolds.

I think at this point you could provide some restriction to the side that seems to have too much flow and see if you can balance things out. Hopefully the temperatures will be somewhat equal.

Keep an eye on the engine temperature itself to insure that the overall flow is adequate for all speed ranges.

On a marine big block, the water is fed to the recirculating pump and then pumped into the block on both sides, correct? It goes down the block and then to the heads? Then where does it "go" after the heads?

I have a few other things to try today as well. I put a gate valve into the line that is flowing well. Ultimately I may swap that for a manual heater control valve if I can find one that has 7/8 hose barbs or one that is threaded where I can put in 7/8 hose barbs.

Question. When on the lake and in neutral, what's a safe max RPM? I'm leery of rpms IB sn unloaded motor. I would like to run it with the hatch open to see how flow changes above 1500 rpm so I can balance it as best I can across the rpm range. Don't want to starve either side at higher rpms

 

[tpenfield]

SB - Sorry that you have not gotten more responses to your water flow issue. Not a ton of VP experience on forums, generally. I spent an entire summer chasing a moderate cooling/overheat issue on my engines, so I offer what I can, based on that 'experience'.

The water flow throughout the engine is generally controlled at the thermostat housing by way of various chambers within the housing and different opening sizes. You basically have 2 activities going on driven by the 2 pumps

1=sea water pump: pushes water into the engine, displacing the same amount of water out of the engine,

2=recirculating pump: recirculates water through the engine block and heads.

I can give some insight to the water flow, based on the Mercruiser 7.4, as I have a spare thermostat housing handy. I would think the VP t-stat housing would be similar in concept.

1) The cold water coming in from the sea water pump splits at the t-stat housing and some goes straight out to the exhaust manifolds and the rest goes into the engine.

2) As water flows through the engine, it goes to the block and the heads. Most marine engines have 'parallel' flow, meaning that water enters the cylinder heads (from the block) at openings along its length, rather just at one end.

3) The water exists the cylinder heads via the passage in the intake manifold and ends up back at the thermostat housing, although at a different place in the housing (this time at the thermostat itself).

4) At that point, some of the water goes out to the exhaust manifolds and some of the water goes back through the engine again. The sizing of passages within the t-stat housing, along with the current state of the thermostat itself decides how much water goes where. When the engine is cold, more of the water 'recirculates' through the engine. As the engine warms, more of the water goes out to the manifolds, allowing more cold water from the sea water pump to enter the engine.

I have felt that your issue of imbalanced flow out to the the exhaust manifolds is caused somewhere within the thermostat housing. I believe that you have inspected the housing, but I wonder if you have probed the housing with a thin wire and a small flashlight to see if there is something caught in the chambers of the housing or if a wall within the housing has rusted away.

I wonder if a new t-stat housing would not be too expensive, but I know VP parts tend to be about 3X of Mercruiser parts (thieves that they are)

As far as revving . . .

In neutral I would not take an engine up all that much . . . maybe 2K :noidea:

 

[Silverbullet555]

Ted,

I appreciate your replies and your help. Fortunately, were all talking about GM based though there are slight differences. Thank you for taking the time and sharing your knowledge. For several reasons, including pricing of parts, VP is not my preferred choice any more. If I had to replace this engine I would look for ways to mate a merc to the current drive. It likely wouldn't work, but I would still explore it

Back to the discussion.

I thought it might be the water pump so i replaced it. When no change occurred i put the old one back on and will hold the new one for when it is needed.

I too thought the thermostat housing might be an issue so I bought a new one. It was old stock meaning the part number has changed but the one I bought was the original part number. That should've corrected any issues with corrosion or erosion. That could bite me if they somehow improved the newer design and I miss out on that newer design.

If I really knew hydrodynamics (I switched majors from engineering to business) I would explore ways to modify a thermo housing to better split the flow. For now, the valve is in place and I'll see how it works.

I could also have the outlet on the old thermostat housing welded and redrilled with a smaller opening. I'm more likely to have an inline restricting bushing made if I can determine the right flow and orifice size.

It all brings me back to what could've changed that caused this. I don't believe I suddenly became aware of what had been normal for years, though anything is possible. I tend to be pretty aware of noises smells, etc., and that hasn't changed. But, I digress.

 

[Silverbullet555]

Ran it today at the lake. Seemed to do pretty well with th valve. Temps were very balanced. Need to do another set without the kids.

was surprised to get a battery alarm with nearly new batteries. Found some lose terminals. Maybe it caused higher battery drain than normal.

 

[tpenfield]

Aren't boats great? You fix one issue and another one comes in right behind it. . .

 

[Silverbullet555]

Aren't boats great? You fix one issue and another one comes in right behind it. . .

Yep.

Went back out today and she ran well batteries seemed to be fine and indicated they were charging. We'll see what happens when we sit on the hook for a few hours.

now to clean the boat, fix the chartplotter mount and install the onboard charger. None of that will keep me off the water.