(Another) 496 Overheat Puzzle
 

2002 8.1 Gi-b overheats at WOT. Volvo Penta duo prop DPSM Outdrive. Engine rebuilt for cracked piston ring less than 100 hours ago, but about 12 years ago. Seawater cooling system. Boat stored in heated/cooled shop. Inland freshwater lakes only, no saltwater.

Symptoms:

When idle for extended periods temp gauge stays at 150 (140 degree thermostat). Gradually increase throttle to half throttle cruise on plane, stays at 150 for five minutes, then creeps up to 170. Increase to full throttle. Temp creeps up towards 200 within a couple minutes and alarms/derates motor.

It takes almost 10 minutes at idle for temp to drop back to 150.

Steps taken (in order from water intake to exhaust):

Replaced outdrive water pickup bushing, o-rings, cleanout cover gasket and rubber hose. No trash or dirt found. inspected and re-used plastic nipple.

Replaced raw water pump assembly with new OEM pump.

Disconnected intake hose from raw water pump and backflushed power steering cooler and outdrive - all clear.

Did NOT do clear hose intake test to check for air leaks, BUT pressurized system in reverse from raw water pump back to outdrive intake, no leaks.

Inspected transom hose for kinking/collapse.

Cleaned oil cooler intake side, removed a couple of small impellor pieces. Shop-vac'd a gallon of water through cooler in reverse direction.

Replaced thermostat (140 degree) and o-rings, cleaned housing (not terribly corroded).

Reverse flushed engine block drain (winterize) system for 10 minutes - no rust flake or grit.

Removed and inspected circulation pump. No corrosion or wear on vanes, tight on shaft. Replaced with new gaskets. Engine block water inlets clean (light rust color) and free of rust flakes.

Removed/inspected starboard exhaust riser, light rust color, no rust flakes. Power washed, no rust flakes or grit. Water flows freely through riser.

Top of exhaust manifolds are clear of any rust flake.

Replaced riser temp sensors.

Have NOT removed inspected bottom of exhaust manifolds water galleries.

Ran engine with props off, in tub. Suction from water inlet is obvious. Half throttle suction is great. Water output from exhaust and overflow is significant. Video available.

Compression test resulted in cylinder pressures 158-165. No wet compression test.

Leak down results 4-7%. (By this time, I was hoping for a head gasket issue.) Spark plugs are on the dirty/cool side, but uniform.

Since temp gauge and ECU have separate sensors, it seems like they are in sync when engine gets hot, then derates. Therefore, probably not either of those sensors.


HELP!

The hose from the outdrive to the seapump could possibly be collapsing under suction from the sea pump. The first thing I would do is hook up a mechanical water pressure gauge, either permanent, or at least temporary. Don't know a lot about what data you can see with a scanner hooked up on your engine, but you may be able to see water pressure as well.

Not sure if it happens with Volvo's but do a search for bravoitis. My friend had nearly the exact same thing happening as you and his transom hose was partially plugged.

Have you put and IR temp gun on the motor to confirm its actually over heating?

Remove side plates on heat exchanger on front/top of engine. Most likely the rubber gaskets are all swollen and blocking flow. Very common problem.

No water pressure sensor or gauge on this one. I can probably hook up a temporary one inline. I thought about mounting a GoPro back there to watch that hose. Wish they put a stainless steel spring inside or a stiffer hose. What did your friend do? Just replace the hose?

Thanks, but it’s seawater cooled, no exchanger.

I’ll take an IR gun on next test ride. Odd thing is that I can hold my hand on hoses and exhaust risers. I figured that since there are two temp sensors on thermostat housing, one for analog gauge and one for ECU, that they are working properly because gauge goes up then engine alarms/derates.

If you have the funds, pickup a Vesselview mobile dongle ($100 on ebay). It has a bluetooth app and will show you your ECU data in real time including water temp, water PSI, Oil PSI, fuel consumption etc. Nice to have if you cant swing a rinda tool

Which intake hose typically collapses, (13) ps cooler to transom or (6)raw pump to ps cooler? My luck it will be the bottom one that’s nearly impossible to get to.
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OP indicates it is a Volvo Penta so VV is not gonna work.

I had the 8.1Gxi version of this motor and chased similar over and under heating problems with the seawater cooling. I converted to closed cooling (VP makes a kit) and it solved all cooling problems. 496's like closed cooling for the consistent temps.

I checked out the VesselView and it's Mercury only, but Volvo Penta has a version also called Easy Connect.

Seems at lower rpm younhave sufficiemt cooling. After planing throttle levels, it begins to heat up.

Do the temps stabilize at 1/2 and full trottle?

Once back to idle and light throttle it takes 10 minutes to drop back to rated thermostat temps. Once dropped...it can maintain the 140°F?

10 min is a long time to drop temp with raw water.

Where is your water temp sensor located?

What is the avg temp of your raw water source? As in the temp of the lake you run?

Lake temp is 59 degrees. Seemed like a long time to cool back down. It’s a 140 thermostat but temp gauge reads stable at 150 when idling, even for prolonged time.
When advancing throttle to half throttle and planing, it held steady for several minutes then increased slowly to 170. Temp increase seemed to slow down at 170, maybe barely creeping up after 170. Advanced to full throttle and after a few minutes it rose to 190-200 and alarmed/derated. I cut it back to neutral and idled but it took longer than expected to cool back to 150. Hope that better explains it.

I pulled hoses off the exhaust manifolds today and water quickly and freely drained out.

I'm going to replace the plastic nipple going through gimbal although I’ve inspected it end of last season.

There are two water temp sensors, locate within about 12” of each other on the thermostat housing and crossover tube.
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Also going to replace the intake hose from transom to PS cooler, although it feels very stiff and unlikely to collapse. I’ll look through the through-transom pipe to check for corrosion but I didn’t notice any when replacing the transom to gimbal hose.

Temp senders
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Was curious if the half throttle would equalize temp vs water flow etc. Of if it would still have an eventual thermal run-away.

You're pumping water at a reasonable volume at half throttle. Where is the heat coming from? Either the engine is making more of it, or your water flow is restricted. You've changed almost everything.

How is the engine performing? No change?

Are you running a thermostat? What temp?

Have you tried a high volume thermostat?
Or perhaps a restrictor plate instead of a thermostat?

Also, do you have equal water amounts coming out of each exhaust tip (assuming through hull). If so, is water coming out the same temperature?

Engine runs great. Spark plugs indicate rich condition but are uniform. Driving me nuts. Gonna pull transom to PS hose tomorrow and check PS cooler and through-transom tube, but it’s not like a bravo setup so shouldn’t be a problem. Maybe the intake hose is collapsing at high raw water rpm’s.

Running a Volvo Penta OEM 140 thermostat. Not sure if there’s a high volume option. I may pull it out and see if it still overheats. Boat has a Corsa captains call exhaust. Water only dribbles out side ports when solenoids activated. Comes put transom exhaust port and overflows when solenoids not activated.
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Video is too large to post

Yes, he replaced the hose assembly in the transom assembly. I would definitely hook up a temporary water pressure gauge. There may be a port on your intake or t stat housing that you can use or if not, you can use one of the block drains. https://cimg5.ibsrv.net/gimg/www.off...a6dca2ce65.jpg
My guess is your issue could be the hose circled in red. The hose my friend replaced was essentially this hose in a Bravo transom assembly.

That hose was OEM new last year. The lower nipple will be replaced today. Will inspect upper through-transom pipe today. All tstat ports are used. Block ports have drain system but maybe I can plumb a gauge into end of that.

Removed transom-PS cooler hose. It looks fine and is very stiff so probably wont collapse. Was clean on the inside. Bought a new one so will put it in.
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Inspected transom to gimbal housing hose and replaced plastic nipple and o rings. All looked good, but replaced nipple anyway.
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When I had the stern drive off and transom to PS cooler hose off I ran an electrical cord through the transom tube. It when through without any obstruction and was clean. No powdered corrosion or dirt/grit.
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Update - new intake hoses installed, new temp sender to ECU installed, manifolds and risers flushed through thermostat housing hoses (all clean and free flowing), oil cooler tubes cleaned with long brush and pipe cleaners (no surprises). Installed 0-30 water pressure gauges on engine block drain hose and exhaust riser.

started boat on the hose muffs, inside a water filled tank. Idled and water discharging until temp rose to 150. (140 thermostat). Zero water pressure on block and riser. Removed hose muffs. No change in pressure. Increased rpm to 2000, still zero on gauges. Water flowing from discharges. Temp never got above 150.

IR temp gun confirmed no temps over 145 anywhere on system. Oddly the port riser and manifold are 20 degrees warmer than starboard. Hose feeding manifold from thermostat housing also about 15 degrees warmer than hose from same housing feeding starboard manifold. Go figure. Check thermostat housing nipples - all clear.

Zero pressure? Maybe no restrictions means no pressure?

Headed to the lake this morning.

It is normal fro the 20* temp difference from risers.
Idle water pressure is usually only about 2psi.
Pic of how water pressure gauge is installed??

Well f-ck. Temp gauge quit working half way through test. Gauge matched IR gun up to that point. Half throttle no temp increase above 150 at the sender. Full throttle five minutes then engine alarms and derates. IR gun temp at sender was 227! Had to be steam since it’s lake water. Again took several minutes to drop. Attempted to pull thermostat but hose removal wasn’t possible due to high temps. Gonna pull and test (new) thermostat and replace (new last year) impeller. Then back to the lake. Still no pressure readings on block or risers, even under WOT.

Crossover tube seems to be the hottest section of the cooling system. Goes from thermostat housing to front of both heads. Also has the bung for temp gauge sender.

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2 psi probably wont even register on a 0-100 or even 0-30 gauge. Didn’t know what to expect so started with a high range.

Could crossover tube (between heads and temp housing) be clogged? It’s the highest temp anywhere on the engine/exhaust.

One gauge on riser and one on block drain hose. Not ideal.

Check the cam inside of the raw water pump for wear. Sounds like a lack of water flow. If the cam is worn it wont compress the impeller blades.

Let's back up..........

Is this a new too you boat or did you have the engine rebuilt?? When did this issue start??? Did it ever maintain temp at WOT???

No idea if those gauges with that size hose will work to get water psi. Normal water psi gauges use 1/8 tubing.

This seems inaccurate to me, isn't the the impeller and the cam on the same shaft? So if the cam is worn, the impeller is still spinning the same rpm as the pulley. If the cam was wore he would have low fuel pressure

Ediit: I don't think the 496 came with a fuel pump mounted on the water pump, are you just taking about the "shape" on the inside of the housing when you say cam?

The out of round portion of the raw water pump impeller housing is the cam plate, or cam.

Thanks for the responses. I’ve had the boat for 15 years. Seems like it used to overheat on long, maybe 15-20 minute WOT cruises. Also had a cracked piston ring and had engine rebuilt by a reputable marine builder, Dean Kelly on Grand Lake, OK. Engine ran great after that but I’ve babied it to some degree. One day it started overheating even at low rpm, maybe half throttle. I stopped, changed the impeller, same problem. On further inspection the rear plate of the RWP had a groove, I was told was caused by use of incorrect impeller. I bought a new OEM Volvo penta raw pump with impeller. It helped, but didn’t eliminate the problem, only moved it to occur at high rpm.

Today I pulled and tested the thermostat suspended in a pot of water along with an electronic thermometer (on my multimeter). I confirmed the thermostat tstat I purchased last year was an OEM 140 degree tstat. Volvo Penta has changed their recommendation to a 160 degree tstat for all 8.1’s. The tstat began to open at 157, and was fully open by 160. So much for a 140, ha, but 160 shouldn’t be a problem.

I performed a raw pump flow test by starting engine with hose to thermostat housing removed. VP service manual says to hold hose at flame arrestor level and observe water exiting hose. Says if water head is 1 inch all is good. Said to look take action if below half inch of head. I couldn’t get it level with flame arrestor without flooding electronics, but had a solid 1inch of head when held 5 inches above flame arrestor. I decided not to replace impeller (again).

i also hooked up a garden hose to flush the block and heads and check flow rates via the circ pump hose exiting the crossover tube. Seemed to flow well. But coudnt isolate each bank that way. No grit, chips, discoloration, etc.

im thinking about filling the block and heads with either 30% vinegar or evaporation-rust and let it sit a day or two. No sure about how that would affect circ pump seals or ceramics, or rubber, or head gasket material.

i think that answers questions above and then some. Tomorrow I go to the lake with tstat removed. Not the end solution but perhaps one more pies of puzzle.

you say 8.1L,isn't the motor closed cooled?if it is,take the heat exchanger to a radiator shop and have it cleaned.I chased an overheat problem on a big tub and thats what fixed it.good luck,keep us informed.

Thanks, but it's open cooling, "seawater cooled", no exchanger.

I emailed CRC, the manufacturer of Evapo-Rust, asking if their product would harm the brass, ceramic or rubber on the circulation pump, or head gasket material. They said that their product would not harm any of those materials, only rust. I plan to warm up engine, remove thermostat housing, drain block and heads via the winterization hose, then raise same hose above engine and pour Evapo-rust in until liquid appears in top of thermostat housing. Block and heads should be full. Let sit for 3-4 days then flush. Product won't arrive until Monday, so maybe I get a short vacation from the boat. Still planning to run it tomorrow with no thermostat. Not sure that really tells me anything, but why not.

Gonna try and find a clear hose to run the VP suggested head gasket leak test. From VP service manual:
Replace water hose(s) between thermostat housing and exhaust manifolds with clear plastic hose. Operate at rpm at which overheat occurs.
No bubbles evident, head gasket not leaking. Bubbles evident, head gaskets leaking.
They then suggest a compression test and to check spark plug condition. I did all that and a leak-down test first, but engine was cold. Gonna put the plastic hose in anyway, since I'm running out of ideas.

Has anyone used some kind of aftermarket "cup" to install on outdrive by water intake holes to help force water in at speed and increase water pressure? Buddy of mine said he did it on a bass boat years ago. I can't find any kind of commercial product.