Merc 225/302 Ford Running hotter than I would like

M

motogizmo

New Member
Apr 9, 2012
92
Washington
Boat Info
1973 SRV 240 fly bridge
Engines
302 Merk
The condition is on a boat new to me. SRV240, TRII outdrive, Fresh water cooling. She is running hotter than I would like at 3200 plus RPM. I would say 180 to 190 Degrees. Can't test it at this point. I have a point and shoot thermo reader, but sourcing parts is keeping her out of the water. She comes up to normal operating temp very fast and stays there at an idle. Hit the gas ans she climbs fast. I figured that it was an automotive 180 degree thermostat, but on inspection I found no thermostat.

At this point I have checked:
1. Water intake strainer is clean.
2. Water pump has a new impeller.
3. Trans cooler is new and clean.
4. power Steering cooler is clean.
5. Fresh water cooling tank is clean.
6. Exhaust risers are clean.
7. Nipples on the risers are not bottomed out.
8. Exhaust flappers are total gone. (I have new ones on order)
9. I have checked the drive for pieces, but have not taken it apart.
10. All the hoses are new and the right type.
11. Water and exhaust are moving though the drive.

On the engine:
1. New 140 degree thermostat.
2. New hoses.
3. Good visual check of the water pump it is flowing coolant.
4. The exhaust manifolds are new.
5. The thermostat housing has been cleaned and painted, the bypass is no longer obstructed.
6. Cap seems to be in good working order.
7. The timing is spot on.
8. The carb is running a little rich if anything
9. The fresh water cooling is OEM Merc.
10. There is no evidence of a blown head gasket.
11. Engine has 60 hours on it.
12. Oil looks like new

I plan on taking her out and testing again with the laser temp reader. The gauge could be off, but my nose and hand say it is right. What am I missing here. I know 180 to 190 is, but not with no Thermostat. She comes up to temp fast. I feel she should be at 165 tops. I know this topic has been well gone over, but after 3 hours of reading back posts, I have no new ideas and no smoking gun. Thanks in advance for your reply's.
 
Last edited:
Well it does surprise me that no one has posted anything at all about this. So were I stand is still waiting for parts to test this unit further. I have one of 2 options.

1. put it back together and take her to the lake and test it with the exhaust bellows on and watch the temp. Then remove the bellows and test again. That will show if there is a restriction in the drive, if the temp returns to normal without the bellows installed.

2. I could scope the drive to see if the flappers have lodged in the drive, and are restricting the flow. It is 80$ for the scope.

There is one other possibility. Being that the heat exchanger was mounted in the wrong place (on the back of the engine), and that most of the hose fitting were home made this cooler may be too small ( or the wrong one for this application) for the way it is plumbed. The plumbing diagram from Merc shows the manifolds cooled by the heat echanger. I have read one post were an after market heat exchanger was installed on a big block and it could not deal with the heat produced by the exhaust. They ended up cooling the manifolds with raw water and that fixed the issue. I can not find any numbers on the exchanger, but it looks like the one in the Merc Manuel, the seals and zinks are the ones that are called out for my engine with closed cooling, and I have it plumbed per Merc's spec.
 
Motogizmo, ain't nobody replied most likely because there's 2.4 billion posts on the subject... Only teasin'.:grin:

I have a raw water cooling system that was giving me fits on a brand new engine. Advice from folks here, 2 different Merc techs, and a bunch of others all had different ideas. The day I dropped it in the water I was cruising along slowly at about 1500rpm, and saw the temp go from 150 to 200. Before I could reach the throttle to power her down, she went right back to 150. Hmmmm. Then for about a week it'd go from 150 to 175 while cruising around at about 1000 rpm. Now, she stays at about 160 throughout the rpm range Took her out on the river with the laser thermometor, and nothing went above 160, but did get different readings all over the place.

I went through absolutely EVERYTHING on the boat, drive, etc. You name it we checked it. Finally just said the heck with it, it's not going above 175, so I'll live with it. Don't know if that's the best attitude or not, but I'm sure as hell not gonna sit at the dock because of it.

Point is, cooling systems can frustrate you very quickly. Your thermostat was removed for a reason, probably to combat the hot running you're experiencing now. I even pulled mine, and it didn't make much of a difference at all.

Good luck in getting this fixed, hope you're on the water sooner than later.
 
So I scoped the drive today and found none of the exhaust flapper stuck in the drive. I did get the number off of the heat exchanger. It is a 441713
 
Those temps are from the gun not the gauge right? So you've ruled out the gauge.

My "guess" would be the homemade cobbled up cooling system. Thats the obvious culprit since it doesn't follow the OEM. At least thats where I would start. Have you shot temps on that system to see how much, if any it changes through out?
 
I can find the part number for that cooler on the web. It is 20 inches long with a 4 inch diameter. The fresh water tank is 16 inches long with a 4 inch diameter. It is a mercruiser part. These dimensions are correct for my motor with the exhaust manifolds included in the fresh water cooling system.
 
Rick K thank you for the input, If I was lake cruising I would just go with it. We are setting up for Albacore Tuna fishing 50 to 80 miles off shore. Jim aka Mopar has a thread going were the current hypothesis is that running without a thermostat on some engines my cause mild over temp problems. I have the cooling system as stock as it can be. Now for the test. The lake were are putting in at on Sunday runs 60 to 64 degrees. If she stays cool there she will stay cool in the open pacific.
 
Last edited:
So we had her out today. Conclusion is that putting the thermostat and the exhaust flapper back in made no improvident. Water temp in the lake was 64 degrees today. If anything she ran just a little hotter. The IR shows that the intake on the fresh water cooling was running 125. The heat exchanger was 155 on one side and 165 on the other. The exhaust manifold is 175 where the cooling water enters them, and 220 where it leaves the manifolds. The main pipe returning to the heat exchanger was 175 degrees. The block was all over the map from 155 to 185. The thermostat housing was 145 at 1200 RPM and 155 at 3200 RPM.

The good news was that there was only about 10 to 20 degrees difference between 1200 RPM and 3700 RPM. The gauge is reading a little on the high temp side, but it is not totally wrong. I am going to install a matched gauge and sender set this week.

SO HERE IS MY BIG QUESTION..... WHEN YOU HAVE THE PRESSURE CAP OFF AND THE ENGINE RUNNING CAN YOU SEE SIGNIFICANT FLUID MOMENT IN THE TANK OF THE HEAT EXCHANGER??????????? I ask this because I am not seeing the moment that I think should be present. I will remove the block water pump and inspect it just to be sure there is no issue there. It is the only part I have not had in my hand and under a big light!

Here is a pick of the gauge at 2000 RPM
IMAG0754.jpg


Here is a pick of the gauge at 3200 RPM
IMAG0758.jpg
 
Ok so I found the smoking gun! I scoped the coolant side of the heat exchanger and found it! It was a bunch of crap in between the cooling tubes plugging it up. Chunks of rust, bits of sealant, and some crystal looking structures that I would have said were salt if they were on the raw water side. I tipped it upside down and ran some water through the exchanger and got out some samples for a picture. Now how do I get the rest of it out. There is lots of it and it is down in the cooling tubes. I have herd of using caustic soda. The radiator shops around here can't clean them any more for EPA regs or something like that. Any ideas? I wish it came apart. I may look for a used one, but I may end up with more issues than I have know.
IMAG0761.jpg
 
Last edited:
Thanks KAZ911. I have spent the last 3 hours looking into fixes for this problem. Seems to effect marine heat exchangers of types and sizes. Funny I had never hear of this as a problem, but that does not mean much. All of the reading I have done recommends an ACID based cleaning by a professional. Past experience tells me that in my area this is not an option. So I am doing a test. I have set up 3 small cups:
1 has CLR in it.
2 has Draino or caustic soda in it.
3 has meradic acid in it.
I have put a new penny in each one. the plating on the penny is .000327[FONT=arial, sans-serif] inch thick. I will wait 8 house and see how the copper holds up in that amount of time. If the penny is gone, or the copper is completely gone I am not going to use that solution in full concentration for 8 hours. I do realize that following this path my lead to a new heat exchanger. The solder may not take the acid as well as the copper does. Either way I will look at my options after a good nights sleep and a review on my results.

Any guess as to what I will find in the morning? I am betting that the CLR will do the most work and eat away at the metal the least. Being that large rust partials and the mystery crystals are the biggest problem, I will need to shrink them down in size to flush 100% of them out of the system. After the caustic cleaning I will use a strong cleanser like simple green and a re-circulation pump to back flush the exchanger for a good long bit. Then a good pressure test.[/FONT]
 
motogizmo said:
Thanks KAZ911. I have spent the last 3 hours looking into fixes for this problem. Seems to effect marine heat exchangers of types and sizes. Funny I had never hear of this as a problem, but that does not mean much. All of the reading I have done recommends an ACID based cleaning by a professional. Past experience tells me that in my area this is not an option. So I am doing a test. I have set up 3 small cups:
1 has CLR in it.
2 has Draino or caustic soda in it.
3 has meradic acid in it.
I have put a new penny in each one. the plating on the penny is .000327 inch thick. I will wait 8 house and see how the copper holds up in that amount of time. If the penny is gone, or the copper is completely gone I am not going to use that solution in full concentration for 8 hours. I do realize that following this path my lead to a new heat exchanger. The solder may not take the acid as well as the copper does. Either way I will look at my options after a good nights sleep and a review on my results.

Any guess as to what I will find in the morning? I am betting that the CLR will do the most work and eat away at the metal the least. Being that large rust partials and the mystery crystals are the biggest problem, I will need to shrink them down in size to flush 100% of them out of the system. After the caustic cleaning I will use a strong cleanser like simple green and a re-circulation pump to back flush the exchanger for a good long bit. Then a good pressure test.
Click to expand...

Since it is "old" anyway - I would try something equal to the Synthetic acid from Triton. There is another supplier I can't remember - but that is also "green" acid.

Make a circulation system - so you have a small pump in a bucket and keep circulating the acid through the heat exchanger. Acid standing still is not nearly as efficient as aggravated acid. I would run pump for 10 minutes - then wait an hour - then again and again :)

But a new heat exchanger OEM part is ? $400? So it is not a "huge" bill if you can exchange it yourself. \

If you have a company that does A/C flush'es close by - then they might be able to sell you the acid they use. It is the same (more or less) - or they might be able to do it for you.

/Kasper
 
The company that makes the heat exchangers is up in your neck of the woods (Bellingham,Washington if I remember correctly). I think the name is San Juan Cooling systems. Very helpful people. I I'd try giving them a call to see if either they can service the cooler for you or provide you with some tips. My Dad had them modify his cooler and they did a great job for a very reasonable price. I can get you the contact info if you're interested. Best of luck.
 
MMcCawley thanks for that info, an Juan Cooling systems is a great company that makes good quality products. If I mess mine up they will be on my list to call. I figure I have little to loose. worst case I get a new cooler ;).The good news is that 8 hours in the 25% acid solution did a loot of good. The crystal structures are almost all gone. The debit that came out of the cooler was significant. I am giving it one last soak in 50% draino for 3 hours. Then one more good flushing.

In the mean time I checked the gauge to see were I was really running. I did this by heating some water to known temp using a calibrated thermometer. I then submersed the sending unit with a jumper to ground. The line between the green zone and the red zone is 170 degrees. The middle of the green zone is 140 degrees. I would say my gauge reads 20 degrees hot. Under full power she was running 180 to 185 degrees steady. That is not outrageous. It will be cooler with the crap gone from the heat exchanger.

This is the stuff after 5 or 6 flushings. I should have started saving it sooner. Some of it looked like old paper towel. Just amazing! This is a 50 gallon drum to give you the scale.
IMAG0763.jpg


This is a view of the crystals that were left. just a few were a mountain of them was before.
IMAG0764.jpg
 
Last edited:
So the 3 hours of 50% draino got out at least another 1/8 of a cup of junk. The innards of the heat exchanger are starting to look like brass again, and I can see the wields are tin. There are still a few little crystals that I can see, so there are sure to be ones that I can't see, but I think it is time to stop. It is holding good pressure. It is time to take her out fishing in the salt and see how she does. Thank you to everyone that gave their help to put this one to bed. Ill post the final results from the salt water testing after the weekend. Be safe out there.
 
P.s. Don"t try any of the fixes that i tried in this post unless you are prepared to buy a new heat exchanger.
 
The boat ran at 140 degrees all day. No movement in the gauge from 1200 RPM to 3500 RPM. Perfection!!!!!
 
You must log in or register to reply here.

Forum statistics

Threads
113,187
Messages
1,428,230
Members
61,099
Latest member
Lorenzo512
Back
Top