Overheating problem

I drilled a couple of holes in the thermostat. I don't expect it to solve my underlying problem but it should prevent the high temp spike I saw during warm up. Worse case should be that it takes a bit longer to warm up and maybe runs a bit cool at low rpm. There is a chance that part of my problem was low coolant flow because of a lack of a by-pass and the use of an adapted raw water thermostat housing. If it runs cool enough I suppose I won't know if that was the problem or if it is making up for some other deficiency, but I am not sure I care if the engine runs cool enough and I can use the boat (which at this point will be next year and there after, our season being essentially over). I won't get it back together and tested until the weekend but will let you know if there is any difference.
In the meantime, thanks again for all the responses.

KAG, IMO, the tiny holes in the thermostat flange aid in initial air purging. Once the system is purged of air, the tiny air bleed holes should be sufficient.

I have twin engines that are equipped with half closed systems (engine block/cylinder heads only).
The thermostats do have the tiny air bleed holes in them. The T-stat housings are not equipped with any by-pass porting.
I can assure you that the T-stat housing by-pass is not necessary for a half system.

However, when we bring the exhaust manifolds into the loop (such as your systems), the by-pass does help keep coolant to continually flow through the exhaust manifolds. In your case, the by-pass does make sense.

Your T-stat housings are double outlet.
They also offer the mixing chamber (unnecessary, btw) of which has the circ pump supply and the sea water pump inlet port both capped off.
(who knows what type of turbulence is being created within this unnecessary chamber)



Rather than mess around with drilling holes in the thermostat, and/or porting your already incorrect T-stat housings, why not replace these T-stat housings with a more correct Closed Cooling System T-stat housing.... such as the housing that I presented earlier?????

This one is already ported for a by-pass (clearly shown here). .... and does NOT have the mixing chamber.



Also, get rid of those God Awful house style plumbing components , all of the twists and bends , and install a less restrictive coolant return system.

I'll be bold here and will suggest that you are attempting to put a Band-Aid on a system that is just not going to heal properly.
As you know, if you were to sustain severe over-heating, you'll be looking at an engine replacement.

Correcting/changing/fixing your existing system will be far less expensive than an engine replacement would be.


Hey, I'm in your corner, KAG........ I just hate to see you chase your tail here.

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Rick:
Do you know a part number for the proper thermostat housing?
As to design of the H/E system, the only change I can think to make would be to swap ends for the coolant so that it comes out the end the pump is on which would eliminate the pipe and a turn. (ordinarily you would want a counter current exchange but since my raw water is down and back swapping the coolant entry/exit shouldn't matter) Or, I could replace the whole system. Any suggestions (part no. reference) as to what a proper replacement would be? I hate to do that not only because of the cost and work but because this one worked for a long time and the problem that caused this year's overheating in the first place may not be fixed by a new H/Ex (but might be masked or made up for if it has greater capacity).

KAG, Crusader thermostats come with the holes pre-drilled. I just replaced one on my 454.

Man, I hate to put myself in a position of recommending parts when I'm not there to physically see your system.

If these once worked sufficiently, something has changed.
Your job is to find out what changed.
During the process, it certainly won't hurt if you were to remove some of the restrictions, and perhaps replace the T-stat housing with a correct style.

I'd again recommend that you take the H/E's in for professional service.
You cannot see the E/G side of the tube bundles.
You might be able to do a mild chemical cleaning, but you won't get the job that the professional will give you.


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craig_collins said:

Rick, Crusader used the same T-stat housing when they built these older motors and plumbed them accordingly if the boat manufacturer wanted raw water cooled or fresh water cooled.

Click to expand...

I just now read your post.
Are you suggesting that the same T-Stat housing was used for both RWC'd and Closed Cooling systems....... and that the two ports were commonly capped off?

Yep. I know my 1981 Egg Harbor fresh water cooled came that way from the dealer and an old Crusader mechanic told me the same thing.

Put it back together today and went for a little ride. Holes in thermostat affected warm up, as expected. At cruising speed it seemed to run a few degrees cooler, but I noticed that the ocean has cooled from 74 to 70 so that may be why.
I am ready to give up. I will probably ship the heat exchangers off over the winter to have them chemically cleaned, just to be sure. But I won't know if that changes anything (given that one engine was fine and switching the heat exchangers did matter I doubt it will) until next year. I may also try and streamline the system a bit, which won't solve the problem but might help compensate for it. Other than that, I don't know what else to try.
Thanks for the suggestions. Let me know if anyone has an eureka moment.

Thermo-Electron wouldn't have gone thru the expensive of adding a set of new parts if there wasn't a good reason for it....they (and Mercruiser and GM) don't like to spend money without good justification....think about it.

Still working on this (really more thinking about it and asking people for suggestions). Anyway:
It has been suggested to me that running too lean can lead to overheating and could be the source of my problem. I don't know that it is too lean and can't do anything until spring, but is it possible? Any comments?

you have an IR meter. Here are the options as i see them:
1. low coolant flow; you will see hotter than expected coolant into HE and colder than expected out of HE.
2. low raw water flow; you will get steam, and hotter than expected raw water HE output
3. loss of HE efficiency, but has good flow; no steam, hot coolant HE exit temp, cool RW output
4. air in either RW or coolant system; includes strainer leaks, combustion gas getting in.
Those are the big 4 for system issues. Each breaks down into possible causes. Your engine needs no MODS to run correctly, even in 85 degree water.

A lean burn will deliver more heat into the exhaust manifolds. Is this a full system? Do the spark plugs look overheated?

See post #62 again.

KAG said:

Still working on this (really more thinking about it and asking people for suggestions). Anyway:
It has been suggested to me that running too lean can lead to overheating and could be the source of my problem. I don't know that it is too lean and can't do anything until spring, but is it possible? Any comments?

Click to expand...

Operating a Marine SBC while too lean will cause the dreaded Marine Engine Load Detonation.... of which will increase cylinder temperatures substantially.
However, rarely does a SBC Marine engine survive Detonation for any length of time.


Edit:
I see what looks to be a Mallory ignition distributor. Most likely mechanical advance... yes/no?

Rusty or Corrosion compromised flyweight returns springs will allow the spark advance to come on far too early.
Spark advance too early will most definitely lead to Detonation...... but again, rarely does a SBC Marine engine survive Detonation for any length of time.



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Diver Dave:
If by a full system you mean coolant (not raw water) goes through the exhaust manifolds then yes, it is.
I did not look at the plugs (didn't see any reason to, it ran fine). I don't think doing so now would help much because of the fogging I do as part of winterizing.
One new thing I did do was put in clear hoses between the manifolds and HE to try and judge coolant flow. At anything above idle there are air bubbles in the flow (which get smaller as RPM increases). I know air can reduce heat transfer but don't know how it gets in there (am pretty sure it is not combustion gases) and see a similar result in the other engine.

There will be some air in a typical HE, unless you have a coolant recovery system. Any combustion gas will want to push out the pressure cap and you should be able to easily detect that. I tend to think air is worse in the raw water side, since it means the pump is picking up air from the strainer, usually. That can be the source of trouble. Perhaps do the clear hose on the RW side.