FWC Overheating > no thermostat and zinc gone

[Bretthski]

Experienced our first overheating this weekend > Running for 10 min before I noticed appx. 200˚ before I shut her down. Thankfully the winds were great we sailed the entire journey giving the engine enough time to cool only to set the anchor.

Our 1975 C&C33 came with a new A4 from MMI (still in the break-in period!). Besides change the oil, plugs and fuel filters, I haven't touched the engine nor the FWC system in the 3 seasons we've owned her. I thought with a new engine there's not much I need to do, right? Wrong.

The forums have been so helpful:
1) Must be the thermostat – so today I checked and NO thermostat installed! (there is a 160˚ one that came with the boat). Note-1: There is thermostat housing spacer installed. Note-2: Cooling system bypass kit has also installed and set to full open.
2) I check the sacrificial zinc anode at the HX and it was GONE. Just the plug. The hole was completely blocked with crud so I cleared it out with an awl and got it draining nicely again. Zinc replaced.

I have my thermostat housing off and now wondering what to do next?
> Install this existing Tstat that I have here?
> Order one of the MMI 150˚ thermostats?
> Keep it as is with NO thermostat?
> Was the plugged HX from the zinc causing it to not be able to cool the coolant?
> Do I need to install new gaskets the Tstat housing?

Thanks all!

[Dave Neptune]

First welcome to the MMI forum.

The bypass should be mostly "CLOSED" to force the water through the block to cool the engine. Closing the valve increases cooling and opening it increases the heat by bypassing the coolant around the engine and not through it. RE the t-stat it needs to be the correct style double action style not an automotive type. Before fussing with the t-stat I would start the engine again and have the bypass valve completely closed and then observe the temp. You could post a pic of the t-stat however there are a few different styles of cooling systems available and having a spacer you just may have one of them, again someone may be able to identify your set up with some pics.

The HX itself could be gunked up and in need of flushing or the water flow from the pump may be restricted. Do the above first then the condition of the HX and/or block can be evaluated. The HX can be soaked in vinegar for a few days and that usually cleans them up as well as the block pretty good but first do the temp check with the bypass valve closed. If your running coolant in the block it should still be clean and not gunked up.

Be sure you have a good flow of water out the exhaust too.

Dave Neptune

These A-4's are quite tough so I doubt you hurt anything.

[Bretthski]

Thanks Dave! Pix of my existing thermostat. It was in with a bunch of old used parts.

Shouldn't it have a thermostat? It appears it can work without, but wouldn't it be better to have a Tstat vs not?

The engine has the Tstat housing spacer installed. Why?

That MMI Tstat looks bad ass/forever. Get that or the even more expensive Tstat?

Think I should remove and clean out the HX? So much crud came out that hole. Would that constrict the coolant flow though? To note, Seawater is pumping out back nicely.

I did change out the FW impeller 2 seasons ago (FW pump is at the back below distributor, correct? Easy with my reverse mounted engine and v-drive) but I have not checked or changed Seawater impeller at the front above the flywheel housing – NOT easy access.

I'll check the FW impeller when I head down the boat tonight. Any other pix needed for reference?

PO had the boat for 40 years and struggled with the orig A4 so they put in a new one from MMI. I'm surprised the PO had that valve open instead of closed with the Tstat removed with his many years of A4 ownership. Although PO was clear that this was a FWC... a big addition, so maybe it was new to him as well?

[Bretthski]

Another view of existing old thermostat

[Dave Neptune]

That's a standard automotive style t-stat. Many of us here do run without a t-stat. I did so for 34 years and everything was just fine. Some like to run warmer with an HX as you do get a bit more efficiency with a bit more temp.

The double action type used in the A-4 when open also closes off the bypass so all of the coolant goes through the block and when partially open allows some to bypass to keep the temp up.

Using a t-stat is mostly a matter of choice and I liked the simplicity of less parts so less to go wrong opposed to the bit more efficiency.

Dave Neptune

[Bretthski]

I think I found the culprit. All 6 impeller blades in the fresh water pump were cracked. See pic. New impeller installed.

So... simply bolt back on the thermostat housing with NO thermostat, close the bypass valve and all should be good? What about gaskets? I'd need two with the spacer. And just what heck is that spacer for?? Could I use Permatex applied to both side of the spacer?

Really? No thermostat? You da man around these parts, Dave N, so I'm trusting you

[joe_db]

I think I found the culprit. All 6 impeller blades in the fresh water pump were cracked. See pic. New impeller installed.

So... simply bolt back on the thermostat housing with NO thermostat, close the bypass valve and all should be good? What about gaskets? I'd need two with the spacer. And just what heck is that spacer for?? Could I use Permatex applied to both side of the spacer?

Really? No thermostat? You da man around these parts, Dave N, so I'm trusting you

I haven't had a thermostat in ages.

[Dave Neptune]

Yes Permatex will do the job. Better to use Permatex Aviation grade or #2 than the silicone style on an old engine.

The impeller is a good find, well done. I would change out both though for good measure and future confidence.

I think the spacer was just for the standard automotive t-stat and running without is not an issue. Again ditching the spacer is just one place less to leak, again simplicity or the KISS rule.

Dave Neptune

[Bretthski]

I'd ditch the spacer, but the nuts appear to be welded to the bolts – the entire bolt and attached nut came out when removing the Tstat housing. I think I'd need new shorter bolts. I'll just put it back together the way I found it.

For gaskets, I purchased the Fel-Pro 3060 Gasket sheets set and cut out the 2 Tstat gaskets from the rubber-fiber sheet. I'll apply a smidge of Permatex to get them to stay in place while I assemble.

Lastly there's a green thin film on one side of the thick spacer. Should I try to remove that? It's really on there like it's supposed to be permanent.

Thanks 4 all your help!

[Dave Neptune]

That kinda looks like a gasket stuck to the spacer to me. The spacer shoud be bare clean metal just like the housing and block before the Permatex and gasket installation.

Also remember to torque the housing as it is part of the bolt pattern holding the head (& gasket) down.

Dave Neptune

[Bretthski]

Going back together today. I'll be sure to remove that green gasket before installing. Finally get to use my snazzy new torque wrench!

I'll report back my temp readings with the fixes.

[Bretthski]

On the way to our anchorange, set the bypass valve 3/4 open running at 2000 rpms > 180˚. Bring RPMs down to 1800 and it's about 170˚. Nice!! On the way home, I set the bypass valve to 3/4 closed and that put temp at 160˚ at 1800 rpm and 165˚ at 2000 rpms. PO had the valve set at 3/4 open... per Dave N, I tried opening it mostly. What's the best setting?

[joe_db]

On the way to our anchorange, set the bypass valve 3/4 open running at 2000 rpms > 180˚. Bring RPMs down to 1800 and it's about 170˚. Nice!! On the way home, I set the bypass valve to 3/4 closed and that put temp at 160˚ at 1800 rpm and 165˚ at 2000 rpms. PO had the valve set at 3/4 open... per Dave N, I tried opening it mostly. What's the best setting?

Mine is 100% closed in the summer, I like the engine to be cool(er). 165 is fine too.

[sastanley]

It sounds like everything is working as it should if you can notice small changes in temp when you adjust the bypass.
I totally removed my bypass. I put a bolt in the t-stat housing and in the side plate tee to force all the antifreeze thru the block all the time. I do have a t-stat but ran for years without one also. I think the combination of the HX gunk (that was probably corroded zinc, btw ), and the impellers you found the problem. Be careful making too many changes at once, it gets hard to figure out which was the issue.
I would do a new zinc every season, and impellers maybe every other season, but probably not more than two years on impellers. If those blades break off and get stuck in the hoses somewhere, they wreak havoc.