Running hot!!!

[chiron]

I recently rebuilt my A4 and on its first test run noticed it was running hotter than I remember, around 200*. Through searching this form I found that maybe getting rid of the thermostat would help. I removed it and took the boat out for a 2 hour run to raft up with some friends. With the thermostat removed I was suddenly hitting temps of 220* at 1500 rpm. Max for me is about 1800 rpm.

I am fresh water cooled with a non Moyer heat exchanger. My first thought was that the pump was not working. To test this I, by hand, crimped the bypass loop and inspected the flow of antifreeze through the fill cap. When I crimped the bypass loop things flowed very well, but otherwise the heat exchanger seemed stagnant. I'm rafted up for a week so I can't go for a spin to further diagnose the problem, but was wondering if putting a ball valve on the bypass loop, or getting rid of it altogether would be a solution.

I don't remember reaching these temperatures before my rebuild and am certain I have all the cooling lines put back as they were originally. What could be causing this?

[hanleyclifford]

Losing the thermostat was a good idea and the ball valve in the bypass loop is necessary to regulate temperature.

[tenders]

If you take the thermostat out, you must restrict the bypass hose somehow. I use a short bolt stuffed in the hose. An adjustable valve is adjustable, sure, but my system has run great for 20 years and two or three flushes over that time.

Your symptoms could be explained by a thermostat mounted upside-down.

[edwardc]

Check for a restriction in the raw water side of the HX. The corrosion products from the protective zinc pencil have a way of accumulating and clogging the HX. I had this happen this past spring. Had to pull the end caps and clean out the crud. All runs at 180 now, as before.

[hanleyclifford]

That's a real mess, Ed. I've never understood the theory behind zincs in a copper exchanger; what metal are we protecting the (noble) copper against?

[chiron]

Life has kept me from the boat but I got to take it our for a spin the other day after installing a ball valve. I had the ball valve closed all the way and was running at 180 deg at 1500 rpm, my normal running speed. For fun I increased to WOT and was hitting 200 again. If I ran at 1000 rpm it would get down to 140 deg. Should I be concerned or is all of this in the safe running range?

Our water temp here on the Columbia River is up to 70 deg, and both pumps seem to be working fine, and the heat ex changer is clean as can be with coolant flowing nicely.

[hanleyclifford]

For some reason you are not getting the cooling you should. Are both your pumps Oberdorfer? If so, what cams are you running? Have you done all you can to expedite flow by increasing hose sizes and using cast plumbing fittings? Each connection should be scrutinized to ensure you have the most efficient set up possible. Also, are you certain your antifreeze jacket is full and there are no air pockets? Also, raw water flow can be difficult to quantify. Have you checked the intake system thru the hull for obstructions?

[Dave Neptune]

C, I think you have something that needs cleaning via a vinegar soak of acid flush. If you have descent water flow through the HX and good flow THROUGH (not around) the block it should be running much much cooler. Have you confirmed the gage to be good and/or shot the sender with an IR temp gun.

Dave Neptune

[Al Schober]

Some years ago I had an Onan genset (different boat) with a Sendure heat exchanger. I ended up buying a LONG drill bit to open up the tubes.

[hanleyclifford]

Some years ago I had an Onan genset (different boat) with a Sendure heat exchanger. I ended up buying a LONG drill bit to open up the tubes.

Good point, Al. I've taken the end off more than one Sen-Dure and found 1 or more tubes plugged. It's a difficult diagnosis because even partially plugged the exchanger will give the appearance of normal because the flow will simply redirect to the remaining open tubes at slightly greater velocity, but ever decreasing efficiency.

[chiron]

Good point indeed. I looked inside and it all appeared clean. the symptoms are telling me that at higher RPMs there is not enough coolant moving. Ill take some temp readings the next time I am out. Other than not enough coolant flowing is there anything like timing, fuel mixture, or valve adjustment that could be contributing. I will admit that once I got the engine rebuilt it fired up so wonderfully and sounded great that I never checked timing or readjustment of the valves. It just runs so well I figured why mess with a good thing.

[chiron]

For some reason you are not getting the cooling you should. Are both your pumps Oberdorfer? If so, what cams are you running? Have you done all you can to expedite flow by increasing hose sizes and using cast plumbing fittings? Each connection should be scrutinized to ensure you have the most efficient set up possible. Also, are you certain your antifreeze jacket is full and there are no air pockets? Also, raw water flow can be difficult to quantify. Have you checked the intake system thru the hull for obstructions?

I have the Oberdorfer water pump, Im not sure what cams I am using. What is the cam in a water pump?
Full of antifreeze and there is plenty of water coming out the exhaust, so any issue in internal. When I rebuilt the engine the block, head, manifold and everything I took off to clean was internally clear and clean.

[hanleyclifford]

Good point indeed. I looked inside and it all appeared clean. the symptoms are telling me that at higher RPMs there is not enough coolant moving. Ill take some temp readings the next time I am out. Other than not enough coolant flowing is there anything like timing, fuel mixture, or valve adjustment that could be contributing. I will admit that once I got the engine rebuilt it fired up so wonderfully and sounded great that I never checked timing or readjustment of the valves. It just runs so well I figured why mess with a good thing.

For this and other reasons it would be a good idea to bring dwell and timing to spec. After a reassembly valve lash should be reset. It may simply be that the exchanger is slightly undersized for the application in which case the effects can be mitigated by pursuing better flow everywhere you can.

[roadnsky]

I have the Oberdorfer water pump, Im not sure what cams I am using. What is the cam in a water pump?

The CAM refers to the "Cam Shoe" which is the part of the pump that bends the blades of the impeller to produce the pumping effect in the water pump.
On the Oferdorfer the usual size is either M5 or M7.
(BTW, sold on this site)

In pic #1 note how the "blades" of the impeller are being bent by the cam shoe.

[ndutton]

I think Hanley hit on it and Al followed up. Coolant flow is not expected to degrade since the installation of FWC but raw water flow is a different matter. Any sort of debris or salt encrustation (or a combination) can clog the raw water side of the heat exchanger (see Edward's picture). Raw water flow is just as important as coolant flow. A slight reduction in raw water flow can affect your temp especially at higher RPM where you're producing more heat.