Chronic Overheating

[Sailhound]

Please forgive my ignorance when it comes to this engine, or any for that matter. I purchased the Moyer shop manual and it has gone missing, so I am back to asking questions online. The A4 is overheating. I have removed and cleaned the heat exchanger. Didn't help. Next I will check the impellers which haven't been replaced in at least two years. Why not, you ask? because I have NO idea where they are! I have been told that there are separate impellers for raw and fresh water. I'm assuming they are in a housing on the block where the water intakes are, but before I start ripping things apart, I'd like to know for sure. It seems like I am getting a good amount of raw water out the exhaust, so I'll start with the fresh water.

If that doesn't pan out, I'll check the thermostat. Which means I'll remove it and try it without. In that case, can I use an adhesive type liquid gasket to test it? And when I figure things out, will I need a specific gasket to replace it, or are there universal ones out there?

At normal running rpms, the motor will jump to 200 in under 5 minutes, if thats any help.

Thanks!
Alex

[Mo]

Alex...I've only worked on a couple of boats with FWC. Indeed, it sounds like your raw water side is OK. How is the fluid level in your system. There are a number of things that can cause your trouble and a number of guys here that are pretty good with the fresh water cooling. Before I start sending you on a wild goose chase I'll wait for them to direct you better than I can on the subject. I imagine you will hear from a couple of them tonight or tomorrow...doesn't take long.

PS: Grey or Black (tube) of silicone gasket maker is a good thing to keep on the boat. It can be used on pretty much anything other than gas. When time allows you may order your gaskets from MMI.

[CalebD]

$.02

My engine is raw water cooled so take this for whit it is worth: < $.02.

I do believe that some "FWC" engines run without a T-stat.

Is it possible that your engine block & head could use an acid cleaning? That would entail draining the closed loop of anti-freeze and running vinegar or a stronger acid through it, then re-filling.

I'm not an expert on RWC engines but I do know what a HX is and what it is supposed to do.

[ndutton]

You need to confirm the FW pump is in good working order. Depending on what type of FWC you have and how it was installed it's in one of three places:

Here



or here


or on an odd looking bracket right behind the distributor. The impeller is accessed by removing the cover plate screws (4). Here's where the manual comes in handy. The impeller and shaft can be slid out of the pump to work on the bench. The rubber impeller is held onto its shaft with a retaining ring that most efficiently takes a special tool to remove and replace.

If you find pieces missing off the impeller please report back. We'll have to find where the pieces went, a very real possibility with your symptoms.

All the right parts and specialty tools are available on this site but in your case I'd recommend calling Ken in the parts department. He's a wealth of knowledge.

And yes, lose the thermostat at least until this diagnosis is finished. You can always install it later if you prefer. With the thermostat out you really need the bypass valve to control the flow. As long as you're calling Ken, order at least 2 thermostat gaskets too.

[Sailhound]

Thanks everyone. I'll talk to Ken, order another manual, impeller and gasket kits. In the meantime, I'll pull the hose off the heat exchanger to see if anything comes out while it's running. Coolant level is good. Thank you for pointing out the impeller location for me, it was driving me nuts! I was also wondering about the accuracy of the temp gauge. When it hits 200 it will stick there at times until I restart the motor. Is that a common occurrence?

Thanks!

[Skywalker]

You will get terrific help here from some from very experienced people. This group and MMI are unique.

I have a FWC A4. I would certainly follow the advice you have already been given, but I had a similar situation years ago. Turned out to be a faulty cap on the heat exchanger. I did acid flushes, pump rebuilds, etc until I happened to notice the pressure rating when shopping on line. Mine was letting the coolant blow by.

Every now and then, even a blind squirrel finds a nut!

When you order your stuff, I'd buy one. Can't hurt.

Chris

[Sailhound]

Ok I have removed tstat stuck in water coming to boil and it didn't open. So Iran without the stat and now the gauge is jumping and sticking. So before I rip other things apart. I'd like to check the sending unit, wiring and gauge. The temp will jump around then stick at 240 until turn the engine off, cool off and restart. And when running at a supposed 240 degrees, it seems to run smoothly and without weird smells. Is it possible there would be buildup on the sending unit that would cause this? And is there a standard test to check the sending unit?

Thanks
Alex

[Dave Neptune]

Make sure first

Alex, before going any further I'd check the gage. This is not the best way but it will give you an idea if you don't have access to an IR gun. Get a meat thermometer and hold it against the sending unit and observe as the engine warms. Don't worry so much about the numbers matching just be sure they warms at the same rate.
I'd also check and clean all connections related to the gage before going any further.
If money is available I'd just get a new gage and sender for piece of mind.

Dave Neptune

[Bold Rascal]

Over heating

Hello Alex, all good advice here in the forum but as you may have guessed it, Overheating can a frustrating thing to correct.

Go to Autozone or pep boys or similar and pick up an inexpensive set of automotive guages. The nice set with the faux chrome underdash mounting. the oil and water temp guages are non electric and direct reading.

Just rule out your potentially faulty gage first.

if you are indeed still running hot (180+) take the easiest steps first. Not necessarily in this order...
1) Insure you are discharging (batching) water from your exhaust. Won't be much but it will be consistent. Should be warm but not scalding
2) Make sure your HX is properly mounted or vented.
3) Check your coolant levels, should have coolant within an inch of the fill cap and look inside the HX fill port for evidence of flow. (NOTE!!!! This is done with a cool engine of course)....
4) Remove your T-stat for the time being (some run without it as normal) I run with it. Also check to make sure your T-stat housing isn't corroded up or creating blockages, water should flow freely thru it.
5) Look for kinked or leaking water hoses. or any other water leaks around the block.
6) Remove your heat exchanger, flush it of any debri. Run a small rod or dowel down each interior tube. Replace bad or failing gaskets, Good time to install new pencil zinc.
7) Check your water pumps and impeller's. A recent poster found his cooling issues related to the pump missing it's shoe.
8) Check for blockage or debri's in your water lift/muffler.
9) Remove your engine's water cooling chamber side plate and clean out any build-up between your piston cylinder's. If heavily scaled consider an acid bath)
10) Check the water flow at the exit from your exhaust manifold. Remove the fitting from the manifold and prod it for any loose rust scale or other debris. Especially after an engine flush..

An immediate build up in temp smells of a bad pump or severe blockage on the coolant side.

The Moyer manual is an excellent trouble shooting guide.
Be patient and Good luck!

[Sailhound]

Thank you guys! My new manual arrived, but it says precious little about the FWC system. I have given my HX a UV bath at a rad shop, so it's ruled out. I am running without a TStat. The spiking and sticking gauge is the only indication I have of overheating, and it stays stuck on 240 until I turn the engine off and on again. The engine sounds and smells fine, and I have the usual discharge out the exhaust. I will get a cheap gauge from the auto parts guys next. I am leaving the impeller and water jacket till last, because the gauge thing has me thinking that the gauge or sending unit are the problems, and my water pump and water jacket are so hard to get to.

Thank you again for the comprehensive advice!

[hanleyclifford]

It wouldn't hurt to do a critical examination of your fittings that carry the antifreeze. Get rid of the machined brass sharp 90 degree elbows and replace with cast type used by plumbers. In the process of changing such fittings you may well find your obstruction. In a FWC system it's all about flow.

[JOHN COOKSON]

The spiking and sticking gauge is the only indication I have of overheating, and it stays stuck on 240 until I turn the engine off and on again.

My first guess is a short in the sending unit. If it were me I'd replace the gauge and sending unit and for peace of mind check the wire from the sending unit with an ohm meter for grounding (it shouldn't be grounded) and for continuity.
There are only three items in the circut: Sending unit, wiring, and gauge. This will catch it all.

TRUE GRIT

[Sailhound]

Considering the price, I think I'll go ahead and take your advice and replace the sending unit and gauge with Moyers stuff. It seems pointless to buy a cheap version to test only to have to replace it again.

Thx!