Circumventing the thermostat...

[Mahoneymik]

My A4 has the cooling hose going from the water pump directly into the crankcase through an "L" shaped fitting. Not a "T" shaped one as is shown in the MM cooling video. The water (I assume) goes straight to the thermostat and through it to the exhaust manifold.
Is my thermostat being circumvented? And should I fit a "T" fitting to the crankcase so the thermostat can do its job? I've read here that people have run without a thermostat for years. Is that safe?
I'd also like to replace the cooling system hoses. Does anyone have any suggestions on what kind of hoses I should purchase?
Thank you!
-Michael.

[Mo]

I don't use a T stat on my RWC and I doubt there will be one in yours. Sounds like he has the by-pass out of it so you get a cool running engine. Over time on long runs it will warm up but not on short runs.

I figure it's up to you if you want to put the by-pass loop back in there and put a valve on it. Previous owner sell you a boat with a "purring engine"? ...IMHO he was doing something right.

[ndutton]

I see a potential problem

Speaking to the late model cooling system (I learned my lesson), if you're running with a thermostat and no (or closed) bypass, when the engine is cold the flow to the manifold is restricted, bad idea. You want full flow to the manifold at all times to counteract exhaust heat.

For this reason, not to mention safety, removing the bypass indicates thermostat removal too.

[Mahoneymik]

Hah! Exactly right

The engine does purr. Sounds new.
So I guess I'll just leave it the way it is.
Thanks for your help!

[Mahoneymik]

Speaking to the late model cooling system (I learned my lesson), if you're running with a thermostat and no (or closed) bypass, when the engine is cold the flow to the manifold is restricted, bad idea. You want full flow to the manifold at all times to counteract exhaust heat.

For this reason, not to mention safety, removing the bypass indicates thermostat removal too.

Hmmm... Two opposing views. It seems that the engine was designed for a thermostat. My gut tells me there should be one.

[ndutton]

Hmmm... Two opposing views. It seems that the engine was designed for a thermostat. My gut tells me there should be one.

The engine was designed with the bypass too so doesn't the same logic apply? Having a thermostat makes the bypass important.

[Mo]

The engine does purr. Sounds new.
So I guess I'll just leave it the way it is.
Thanks for your help!

This removing the T-stat is not new...there's a 40 yr history of it here. Very few A4's around here have them...if you get caught in a storm outside the harbor it's wide open to Europe...the engine has to work and work hard if you go for it.

[msauntry]

I tend to see the tsat removal issue as a work around of other problems.

Sort through whatever problems the engine has instead of working around it. If its overheating or running rough, its asking for your help. If its plumbed weird, lets get it straightened out.

Do those running without a thermostat also remove the thermostats from their cars? Why would the boat be different?

I spent years with RWC and it worked fine with the thermostat. Why not have it? I changed to FWC only because I added a water heater and cabin heater.

It sounds like the way its plumbed, you probably won't find a thermostat under the housing.

[ndutton]

I'll take this one

I also had a thermostat when I was RWC, a 140° three spring Holley, worked fine. Then the advantages of FWC overwhelmed me (rust inhibitors of anti-freeze, higher operating temp to name two) and a strategy was developed.

Zero clearance at the flywheel eliminated the MMI PTO pump, my personal preference against the auxiliary drive pump eliminated the other. Hello Johnson CM30-7 electric coolant pump. As has been discussed, the CM30-7 is a stirring type pump, plenty of flow to do the job but vulnerable to restrictions. Anticipating its shortcomings I did my best to alleviate perceived restrictions (sideplate Tee in particular) and an acid flush. When all was installed I opted to make the first trials without replacing the thermostat, removed previously for the acid flush. I figured, "Let's see how it performs."

It ran up to 180° under load and sat there rock steady. Well Gee, that was the ultimate goal anyway. Why mess with success? So I didn't, the Holley three spring stat (I love saying this), the Holy Grail of thermostats, rides merrily along in the spares locker.

I don't know that reinstalling the thermostat will make a difference, positively or negatively, and frankly in my case it doesn't matter anyway. Engine runs under load @ 180°. What could be finer?

[romantic comedy]

I have the original t stat with FWC, runs at a steady 180.

[JOHN COOKSON]

I have the original t stat with FWC, runs at a steady 180.

I have the original t stat with FWC, runs at a steady 145-150.

TRUE GRIT

[Dave Neptune]

Choice FWIW

The temps that we run our A-4's at is somewhat dictated by the type of cooling fluid and or exchangers for other reasons.
If in salt water you are restricted to staying in the 140 range because of the salts.
If in fresh water you can go higher even to 180 or more before deposits from even fresh water start to appear.
If using a heat exchanger you can go to 220 if you want using the "anti freezes" available with a heat exchanger.

Those are just basic restrictions. Now due to the use of "hi-nickel" blocks and a slow turning engine "temperature wear" factors are pretty much moot.

My choice is to keep the cabin cool as my engine is amidships, so I run just below 130 at cruise which works out to be around a 140 degree block when shut down (shut down temps matter) and I am a raw salt water cooled A-4 with no t'stat since 1983 and thousands of hours at that. I would like to go to a heat exchanger for block erosion issues and if I did I'd still run her at the 130 to keep the cabin cooler.

For those concerned about temps my engine should serve as a bit of a ray of confidence that it won't hurt.
Don't forget that you can control temps with the bypass too, I keep mine partially closed to keep the temp down and I can bring her up to over 160 if I want just with the bypass. A t'stat is definitely easier and also an additional point of failure for those following the "KISS" rule. Truly a "choice".

Dave Neptune