Volvo 4.3l's T-stats sticking open - driving me crazy

Technologic80 · **Posted:** Tue Jun 12, 2012 10:06 pm

I replaced both my thermostats when I bought the boat because the last owner told me the engines never warmed up.

Both of the original thermostats had crud on the seat of the thermostat, holding it slightly open, allowing the engines to never warm up. I replaced both of the t-stats and saved the old ones as spares..

Well since then, Ive disassembled and cleaned the thermostats 5 times now!!! They keep getting clogged open with little pieces of grit. I dont boat in shallow water and havent hit bottom. Presumably, this was the same thing happening with the last owner because the thermostats were clogged open with the same kind of grit when I replaced the originals. Ive put 15 hours on the boat since I bought it and its still happening.

As it stands right now, my engines never heat up past 100* mark on the gauges, unless Im idling. Then they go to about 105*. My gas mileage is god awful and I dont like to run the engines that cold, it cant be good for them to be cruising at 3300 RPM and be less than 100*. I know the gauges and sending units work because when I clean out the t-stats every time, for 5 or 10 minutes the engines run at 150* or so, but get stuck open again.

I was thinking of removing both thermostats and running the boat for the weekend like that. Maybe blow out whatever crud is in the block? Any suggestions?

ric · **Posted:** Tue Jun 12, 2012 10:11 pm

Fix the cause, not the effect. If you have rusty metal crud clogging your thermostats that's a serious problem. Something is falling apart, and that needs to be fixed!

Technologic80 · **Posted:** Wed Jun 13, 2012 8:22 am

ric wrote:

Fix the cause, not the effect. If you have rusty metal crud clogging your thermostats that's a serious problem. Something is falling apart, and that needs to be fixed!

Well, its not rusty crud at all. Its more like large pieces of sand. Which is funny because I know the boat, its a freshwater Lake St Clair boat, there is no large sand grains. lol

Anyways, how would one go about getting that out of the system? I thought of backflushing the engine at the t-stat housing but Im not sure where to start.

When I remove the t-stats, the intake manifold is clean. Ive verified this by using a wet/dry vac and sucking it out, feeling around in there too. I googled the problem and it appears Im not the only one. But there isnt a verified fix for the problem out there.

Would it be a big problem if I took both of the t-stats out and ran the boat for a weekend like that?

97_245_sd · **Posted:** Wed Jun 13, 2012 9:04 am

One idea is an old hot rodder trick, for temporary use, is to find a washer with the same o.d. as the thermostat and a large i.d. hole. This would restrict some flow so the engine wouldn't be running too cold but would allow any of the particles to pass through without getting caught. Just make sure it stays in place and doesn't come loose to cause any other problems.

Technologic80 · **Posted:** Wed Jun 13, 2012 9:18 am

97_245_sd wrote:

One idea is an old hot rodder trick, for temporary use, is to find a washer with the same o.d. as the thermostat and a large i.d. hole. This would restrict some flow so the engine wouldn't be running too cold but would allow any of the particles to pass through without getting caught. Just make sure it stays in place and doesn't come loose to cause any other problems.

Lol...sound feasible but do you realize my luck already? I can just see that washer slipping off and doing more damage.

Its a very common problem with the marinized 4.3l (google it!). Ive read of people trying to backflush and then flooding the cylinders, Im not comfortable backflushing. I was thinking of taking off the hoses at the lowest point and seeing if I can get anything out of them, but the particles are so small I wonder if Ill find anything.

The engineer inside of me was thinking. I wish I could create a small conical shaped fine screen to go around the thermostat itself to catch any crud. But that sounds like Im thinking too much too early in the morning

Anybody see an issue with removing the t-stats and running for the weekend like that?

SeriousRob · **Posted:** Wed Jun 13, 2012 11:40 am

No problem running without a thermostat. I never run one in my racecar.
Also, as previously stated you can cut a piece of stainless the diameter of the thermostat opening and drill a 1/2 inch hole in the middle. Insert this in place of the thermostat. Test it out and note the max temp when warmed up. Increase or decrease the size hole until you get the max water temp you want.
The only downside to this approach is that it will take the engine a bit longer to warm up.
Good luck
Rob

Technologic80 · **Posted:** Wed Jun 13, 2012 11:47 am

SeriousRob wrote:

No problem running without a thermostat. I never run one in my racecar.
Also, as previously stated you can cut a piece of stainless the diameter of the thermostat opening and drill a 1/2 inch hole in the middle. Insert this in place of the thermostat. Test it out and note the max temp when warmed up. Increase or decrease the size hole until you get the max water temp you want.
The only downside to this approach is that it will take the engine a bit longer to warm up.
Good luck
Rob

Thanks Rob!! When you explain it that way, it makes perfect sense. I might just try this after all. That way, any crap in the system will blow through the hole because it will be big enough & I will still get (some) engine temperature, no doubt more than I have now - which is 100* and under :roll:

I can try your method out for a week or two and then put the t-stat back in. By then, all the sand/grit will be all blown out I'd imagine.

LouC · **Posted:** Wed Jun 13, 2012 5:06 pm

I have had the same problem, in salt water you can get flakes of rust from inside the engine or sand, but usually I get a season or two out of them before that starts happening. And even so, sometimes if I ran the boat on plane for a while the water flow might flush it out and it would work normally again.
I wonder if you might have a water hose that is delaminating internally and sending small particles through the system. It might be worth it to take a look at the inside of the cooling hoses...

Technologic80 · **Posted:** Wed Jun 13, 2012 9:27 pm

Thanks Louc. I removed both thermostats today.

Same thing - sand and grit in the t-stat seats. Im going to leave them out for a weekend and see if I cant flush out whatever is in the engines.

Its funny because it only takes the littlest piece of grit to hold the t-stats open just slightly, and shazam - thats it, no heat. :evil:

SeriousRob · **Posted:** Thu Jun 14, 2012 6:58 am

Good luck Techno,
I would think anything around 160-175 would be a good temp to shoot for.
My H180 with 5.0 GL runs right at 160 when warm.
Rob

Technologic80 · **Posted:** Mon Jun 18, 2012 11:50 am

Ok so since I removed the thermostats completely, some strange things have been going on :shock:

Yesterday as I was idling out of my canal (5 minutes) the fume sniffer went off!! I always run the blowers for at least 5 minutes before I start my motors, always!! We've had a boat blow up last year at a local marina so Im extra super careful. Heck, most of the times i leave the blowers running the whole time I run the boat.

Anyways, I digress. I was going down the canal and the fume sniffer started alarming. I look over, and the blower was off.. DOH!! I must've hit the switch when I turned the wheel or something. So I turned the blowers back on and the alarm went off after about 10 seconds. For safe measure, I tied up right away and opened the hatches. I couldnt smell anything gas fumey or see anything leaking.

Could the rich mixture from me taking out the t-stats cause this?

Secondly, my starboard engine sounds very "grumbly" since Ive taken out the thermostat. I can explain it but it sounds louder. It kind of vibrates the boat a little too at idle. My tachs arent precise enough to see if its idling rough but thats what it feels like.

Could these issues be caused by it running overly rich? I dont want to damage anything but I DO want to flush out the sand in the engine.

LouC · **Posted:** Mon Jun 18, 2012 2:49 pm

These are fuel injected engines, right so they may be running richer because of the lower engine temp, but I wouldn't think that would cause fuel vapors in the bilge to the point where it would set off the alarm. I'd look at other possible causes to be on the safe side, that could just be a coincidence. I think if the alarm goes off, there is something wrong. I tried some experiments with the one I bought for my boat but have not installed yet. I found that there can be a slight fuel vapor present and it will not go off till the vapor reaches an explosive threshold. I had an open gas can in the driveway, and moved the sensor (connected to a battery in the garage) and it didn't go off till the sensor was really close to the open neck of the gas can. So sniff round the bilge....
Are you absolutely sure, that the particles are sand? Not aluminum corrosion from the drive water passages flaking off? How about the inside of the impeller housing?
I have had this problem as I said but not as much as you seem to be having it. One thing I never figured out, why do the particles not flush out, when you run on plane, the stat is open then and with the water flow through it you'd think it would flush them out. I have had that work a few times but not always.

ric · **Posted:** Mon Jun 18, 2012 3:31 pm

Without thermostats the engine won't reach operating temp and the fuel injection system will run in it's pre-programmed state of running the engine rich. Since fuel injected engines do not have chokes to block off the airflow to make the fuel mixture rich in cold conditions, they just add more fuel.

Will that damage the engine? Well, that's up for a 50 year debate.. but it will damage your bank account due to the loss of fuel economy.

As far as the alarm? Only one thing comes to mind since it only came on with engine running rich: Exhaust leak

Technologic80 · **Posted:** Mon Jun 18, 2012 7:42 pm

Thanks for the replies.

So.. earlier I decided to change my fuel filters/water separators because I dont know when the last owner did (he tells me he did it last fall but I'd rather be safe than sorry!). I purposely turned the fume sniffer on because I knew taking the fuel filters off would create fumes in the bilge. It didnt go off :?:

But the other day when it alarmed, I opened the hatch and there was no gas smell at all. Today, tons of gas smell from me changing the filters and it doesnt go off??!! I dont get it.

Anyway, Ric - Im going to double check my exhaust clamps and the like. Thats something that I often overlook (but often check hose clamps, battery cables, etc). Thanks for that reminder.

Lou - Im going to put the t-stats back in this weekend. IF they clog again and I have my money on "YES", Im going to take pictures with my EOS camera so I can show you whats clogging up the t-stats. Its like big grains of sand. Black in color. I live in Michigan where there is no black sand...lol.

EDIT: Ric, I just remembered that day, we had a following wind out of the canal and we had terrible station wagon effect. The first mate was complaining (nothing new, lol). Could that have set off the sniffer?

LouC · **Posted:** Mon Jun 18, 2012 7:52 pm

That will be interesting to see, black sand like substance, I wonder if it's the seals between the upper and lower drive breaking down, (rubber particles) or a hose, or something from the inside of the power steering coolers??
All I can say is we have plenty of mud and sand, and my mooing spot is only 10' deep at high tide, so it's 3' at low, but when I have had sticky stats, it was more a flake of rust than sand that I have seen in there.

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Volvo 4.3l's T-stats sticking open - driving me crazy

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