Overheat problem Volvo Penta TAMD41B

Hi folks! I'm new here, and looking for advice.


I have a '91 8-meter Cooper Yachts Prowler with a single TAMD41-B turbo diesel engine & VP 260 DuoProp leg. The entire boat & power unit only has 860 hours on it since new.


It's been running beautifully - fast and smooth, but due to circumstances/marital breakup/'COVID-19, etc., I haven't been able to use the boat since last fall. At that time, I was getting 27-28 kts out of her, with 21.5 kts at a comfortable cruise speed.


Fast forward to a couple of weeks ago. I had her hauled out, power washed, changed the zincs, and took her for a spin. VERY fast acceleration up t 27.5 kts (about 3700 RPM), and suddenly noticed the engine temp soaring, and the overheat alarm sounded. I brought her down to idle, and the temp fairly quickly reduced to a proper running temperature. Any attempt to go above 1800 RPM sent the temp climbing.


It was definitely overheating, as the heat exchanger was very hot on the outside (never got much beyond comfortably warm to the touch before, but now it was too hot to touch). Once it had cooled a bit I cracked open the fill cap & coolant instantly boiled up & out. It was absolutely clear, with lots of antifreeze in it, with no signs of corrosion, rust, etc.


The first thing I did was to change the raw water impeller. $100 for the part (I'm in Canada, so parts cost are roughly double what they are in the US). The one I took out was perfect (except for the damage I did to it removing it), and the new one made zero difference to the temp problem.


Over the past few days, I removed the oil cooler (it was spotless inside, and the tubes were clear) and the heat exchanger. There was a fair bit of crud (oyster shell attachments, bits of mussel shells, etc.) and about 10 of the 106 tubes were either fully or partially blocked. It's fully clean now (rodded, used vinegar & water solution several times, etc.).


I just spoke to a mechanic, and he says next to tear apart the aftercooler (due to space issues, a VERY difficult part to service without engine removal in my boat).



I have yet to find a "cooling circuit diagram" for the TAMD41 series engines. It APPEARS the aftercooler is inline BEFORE the heat exchanger, but I can't tell.


Thanks to COVID-19 issues, I'm desperate financially & hoping to figure out a way to get the boat running without spending much more to fix this problem. Right now it's costing $60 +tax per day just to have it sitting on the hard, and the list of gaskets/seals/O-rings just to reassemble the cooler & exchanger run to hundreds of dollars.


If anyone has any sage advice on where to go next, I'd appreciate it!


- Mike

Have you checked the seawater intake path clear? Screen, through hull, seacock or valve, intake hose and strainer. Ensure the intake hose is not collapsing.

Might be obvious, but you didn't mention it.

Does your system suck up sea water through the drive leg, or does it pull from a through hull fitting? In either case the suction path can get fouled while sitting. Sounds like the boat sat in the water since last fall.

A good way to tell if the sea water flow is restricted is to get engine under a load and check the temp of the water going into the exhaust mixer (exit from heat exchanger). Normal for that to be about 10-20F above sea temp. Much above that and not enough sea water flow.

Thanks! It's hard to check that, as it's a hard pipe from the leg straight to the raw water pump, with only about a 4" piece of hose in the middle to allow for engine movement.



I do know that lots of water is running through the raw water strainer at idle (I discovered that when I started to unscrew the top of the strainer housing - a LOT of water comes out at idle!!). As it's a leg, there doesn't appear to be anything inline between the leg & the raw water pump except the hard pipe, and there are no through-hulls, hoses, etc.

Well, sounds like you have done the basics. I am not familiar with your particular engine but the aftercooler/intercooler would be the next logical step in my mind. However I would defer to someone like Ski who is a real engine mechanic. Unfortunately with Volvo parts sometimes take forever to get and are certainly very dear. I was talking to my mechanic and he unsolicited said that he doesn’t like working on Volvos because of those very issues. I have not been a Volvo fan since we had twin duo props in a boat back in the 90s. Even though they were the current year we had a very hard time getting parts for them. The dealer would rob parts from new stock boats to get mine back up. So hopefully someone like Ski will chime in and give you some good advice on which way to go. Good luck and I hope you get it fixed.

Edit, Ski beat me to it, I am a slow typist...

Thanks, Ski! In this case, the raw water comes directly through the leg via a hard line to the raw water pump.


I didn't check the temp going into the exhaust, but that makes sense. I'm assuming it was quite a bit higher than that, although I don't know. Unfortunately it costs me about $450 just to put it back in the water & haul it out again each time I want to test it! Wish there was a way to run the engine up when the boat's on the hard, but I can't see a way to do that....

Get a big plastic garbage can and put the drive into it and fill it with water. Keep the hose running as it may need water as it runs and splashes out of the garbage can. Or put a set of muffs on the intake holes in the lower unit.

Check the thermostat.

My 26-footer was powered by a Volvo KAD44P with 290 DPE sterndrive. In the course of 3-4 months cruising the Inside Passage each summer, later in those summers it would run fine at 7 knots, but when I revved it up to go on plane the temp would sometimes rise more than desirable.

Took me a while to figure it out, but it had been accumulating barnacles inside the sterndrive's water intake slots. I found I could reach down from the swim step and knock them loose with a bent coat hanger, and voila no more overheating at higher power levels. If you have not yet checked those intakes, you might want to take a close look.

Take a look through my tome below. There are a more than a few things to check unfortunately. Result is we can make suggestions but not be able to point to a specific cause.

Maybe this will give some ideas where to look and maybe suggest something you have overlooked.

Well, I'm still at it, and still searching for the "smoking gun". I removed and cleaned out the turbo "aftercooler", including repairing/replacing the mild steel studs that broke off in the housing, despite 48 hours with penetrating fluid etc. (You have to wonder who at Volvo Penta thought that combining steel, aluminum, salt water, and electrical current would be a good idea...).

Anyway, so far the only real blockage I've found was in the heat exchanger, and there was only about 20% or so blockage. One interesting part was that the T-shaped seals (that divide the raw water flow into channels up, down, and back) were all mangled, so they wouldn't have been directing the flow properly.

Interestingly, I found the same in the aftercooler. It appears that the place that was doing a lot of (shoddy) work on the boat previously not only didn't put the divider seal in place properly, but left part of it hanging out under the cover plate & outside the entire housing. That certainly wouldn't have helped, as the flow of the water through the aftercooler wouldn't have circulated as it should. However, this couldn't have been the "smoking gun" as it's been this way for 4-5 years & cooling has never been an issue before now.

As for the raw water flow, at this point I'm not ENTIRELY certain that the raw water DOES come in through the leg. The access to the water pipes & hoses is severely limited & lots are bundled together down in the bilge area & against the transom so it's very difficult to trace where hoses etc. go.

There IS a large through-hull with a ball valve near the transom that I've never been able to identify the reason for. The ball valve works, but I don't know if water flow through it is free. At this point I'm wondering if that's for cooling (it's not for the head - that has its own, brand-new through hull & valve) and, if so, if it's salted almost shut. I'll be looking at that tomorrow (the boat's an hour or two drive away).

I just spoke to a VP mechanic today, and he suggested that another possibility (if the inlet is inside the leg) is that there's a right-angle raw water fitting inside the leg that is notorious for corroding through. He says that when this occurs, the fitting (which is below water line at slow speed) goes above water line when speed increases, allowing it to suck air instead of water. Instant overheat....

The leg is a 290 DuoProp, by the way.

So, he suggests using the existing through-hull (or adding another one, with a ball valve) to reliably feed raw water to the raw water pump, which is only about 3 or 4 feet away from the pump, and to simply not use the through-the-leg raw water supply.

Any thoughts on that?

We had a Seasport with the same engine and same outdrive. Also had overheat issues at speed, and it turned out to be a bad fuel pump. Really good Volvo mechanic here in town suggested it and explained why, but it was years ago and I forget exactly why it caused the overheat, but a new pump fixed it.
Worth looking if the cooling system all checks out.

Thanks, I never would have thought of that! It did get a new fuel pump about 30-40 hours ago (runtime), but you never know, right? I'm guessing that lean running could cause a lot of heat....

******** I'm guessing that lean running could cause a lot of heat....**********

That is gas engine thinking. A diesel does not run lean the way a gas engine does. As long as it gets enough air to burn the fuel they can run effectively and properly.
Diesels do not need a fuel/air ratio within tight parameters like a gasser. They do just fine with what many would call LEAN conditions without getting hot. In fact it is that ability that makes them extremely efficient at low power levels that would give a gas engine fits.

Yours would not be the only leg that has trouble feeding the engine enough water to effectively cool. I don't know about the corrosion allowing it to suck air but others have found the intake has been blocked and couldn't effectively be cleared. THey too eventually installed a proper seacock.

You might try a vacuum guage in the hose to the raw water pump and maybe watch at the strainer for excessive air bubbles. Once running at speed the water flow should be solid with absolutely minimal air.

High vacuum on the order of over 8 or 10" Hg would be too much. Lower is better.

Thanks! I'm going to look at the seacock tomorrow, and maybe I can rig something up.

Well, folks, I believe I found the "smoking gun".


I was looking at the leg, deciding to take a look at the raw water fitting & hose, and saw that there was (deep inside the outboard mechanics of the leg) a large oyster. It had grown to the point that it was pushing hard on the rubber hose, folding it over into a "V", rather than the gentle "U" it is supposed to be. There couldn't be more than a trickle getting through there.


The bad news is, the aluminum fitting that the hose is joined onto is badly corroded (electrolysis, despite my religiously replacing the zincs when they're even a little bit corroded), and needs to be replaced. Aside from the cost of the fitting (which is substantial), it doesn't look like it's possible to get at without removing & disassembling the leg which, thanks to COVID, is waaay outside my available funds.


So, although I now know what was causing the lack of cooling water, the fix may be unattainable.


Unless, that is, I install a new through-hull/strainer/ball valve. That would certainly ensure lots of cooling water, and prevent this from happening again. I would have to figure out a way to plug the very large hose running from the leg through the bilge to the water pump's metal pipe, but that's doable.


Any input on this option? I've had a mechanic or two say it's the "ultimate solution", which makes sense....

Further to the foregoing - I've been reading up on replacing that 290DP hose connector, and it looks like a bear to do, requiring full removal and disassembly of the leg to replace. Hereabouts, we're talking several thousand dollars to accomplish that, IF you can find a mechanic who has time to look at it (currently, none of the 4 I've tried don't have the time).


It's starting to look like the through-hull/strainer/ball valve is the most economical & sure fix for this....

Second that. Pulling water through the leg makes mfr easier, but as things age out having a normal through-hull fitting and strainer is just much better.

Zetec7 you might try giving a call to Advanced Marine in Campbell River, they are the Volvo mechanics up here. They have an extensive collection of good used parts that may be useful to you if you end up having to take the leg apart. You could probably run the question of the thru hull by them as well. We have used them for our engines, they are pricey (but aren't all mechanics) but we are happy with their work. They definately know Volvo engines inside out.



Good luck with your repair.

Well, after talking to a couple of Volvo Penta mechanics, I pulled the trigger & drilled a 1.25" hole through the bottom of the boat, about 1' forward of the transom. I'm installing the same bronze through-hull/strainer/scoop intake that Volvo Penta offered as an option to through-the-leg coolant intake.

I've also added a bronze & stainless steel ball valve shutoff, just in case I get a leak somewhere (something that was never included in the through-the-leg system). At my last survey, the surveyor told me I should consider putting in a through-hull to avoid future cooling problems but, as I had never had cooling problems, I hadn't done it. Now I have...

Now I have to reassemble all the major parts I took apart (heat exchanger, oil cooler, oil filter housing, after cooler, etc.) and get ready for reinstalling them all. The replacement O-rings + one paper gasket cost a whopping $441.41. OUCH! Plus, hauling out & sitting on the hard has cost another $750 (so far), and most of it wasn't necessary....all due to that stupid oyster!!! Up to around $1200 that I don't have to spend.

Well, this answer is a week or so late, but may come in handy for some other things (like replacing bellows) or perhaps helping someone else.....

It’s easy to get access to the corroded water elbow that gave you problems without removing the drive from the boat, and here’s how:

- drain the oil from the drive (it probably needs changing anyway)
- remove the shift linkage cover from the rear top of the drive and unhook the vertical shift link rod that goes from the shift cable attachment up to the shift bell crank (one cotter pin)
- remove the two stainless Allen screws that hold the “steering helmet” to the upper gear case, and push the helmet forward out of the way
- remove the large rearmost hose clamp on the U joint bellows
- remove the two Allen screws at the rear of the upper gear box ( coming up from underneath ) and the two nuts on the side of the upper gearbox....the upper box is now free from the rest of the drive
- smack the side of the upper box with your palm or a rubber mallet and pick the box up off of the drive, twisting it 90 degrees so the splined shaft clears the center section of the drive. Take care of the shims that might stick to the upper box and place them in their normal place in the center section for safe keeping
- pull the box aft and !presto! You have the upper box off and great access to the water feed elbow or to changing the u joint bellows.
- lay a thin piece of plywood on the top of the center section of the drive so “stuff” doesn’t drop down into the drive

Assembly is the reverse of disassembly, except that you use sealant between the center and upper sections of the drive and you need to position the hose clamps that you removed in the exact position that they occupied when you took them off. Otherwise there is the chance of damaging the u joint bellows....

Hope it’s helpful.

Similar problem solved on TAMD41P-A

I had a similar problem - RPM past 3000 drove the temp above the 191 degree specs, so I backed off. My excellent mechanic checked out the exhaust system and found a clog of heavy, wet black stuff partially blocking the system. He dug it out, replaced that hose.

Next time out I ran the RPM up slowly, reaching WOT in specs - about 3775 - and the temp stayed under 190 and when slowing to 7kt the temp fell very quickly to 165. I ran several segments of WOT of 15 min or more that week, and had the same outcome, SOG both ways at 14.8kt at WOT. I suspect too many hours below 3000 RPM for years with no RPM close to WOT are at fault (i.e., ...."My Fault".)

Aside from that problem and fix, I am completely pleased with the Volvo engine and transmission. Runs great, especially with consecutive fuel loads of ValveTect diesel - silky smooth.

This may not be the same problem as with your engine, but this was the problem and solution for mine.

Passagemaker contributor Steve Zimmerman has written several articles about engine RPM, % of effort, fuel burn, engine life, etc., all worth researching. I've been planning to take his diesel mechanics course at Trawlerfest, but COVID got in the way. The class I took from him on selecting a boat, etc., was outstanding - 2016, Kents Island Trawlerfest. We'll take the Boaters' University series this fall including a diesel mechanics course.

Best wishes for an inexpensive and effective solution to your engine problem!

Howdy folks, I'm back!

Well, I went ahead with the through-hull/ball valve installation, reassembled & reinstalled all the the major components (tricky, as some of the specialized O-rings are simply no longer available, anywhere at any price, so I had to re-use some of the 30-year-old originals, smearing them with generous amounts of black marine silicone), and put the boat back in the water.

It started to warm up quickly (which it has never done) and came up to about 165*F in just a few minutes. I did check the in-and-out hoses & pipes from the heat exchanger, and there was a very marked difference in temperature, so that was good.

It got up to 170*F and I was holding my breath, especially when I pushed up the throttle & took her up to about 4K RPM briefly. The temp got up to about 172*....and stayed there. I brought it down to about 3650 RPM (my usual cruising speed, about 22.8 kts) and the temperature never varied. As soon as I brought her back down to idle, she cooled to about 165*F and stayed there. I couldn't get her to go over 172*F, even coming up out of the hole & onto a plane, so I THINK I've fixed it.

No leaks found....so far!

Wish me luck....