TOPIC: Engine Overheating

I am trying to get my 26 ft 1976 Fiberform Boat operating correctly but I keep overheating when the engine is under a load. My engine is a brand new Volvo Penta Ford 351w engine with a nearly new San Juan Engineering freshwater cooling kit. I just built up the engine and plumbing and have it in the boat. I put a new water pump and housing in my Mercruiser 888 stern drive. When I have it on the hose the temperature will not rise enough to open my new 160 deg thermostat? We checked the timing on the engine at it is at 10 deg btdc per the tag attached to the engine. Where else should I look or what else should I try? Thanks much. Tom

OK, this might be obvious, but....

on the hose, you have pressure going in, so not a good indicator of water pump pressure under power. A PIA, but I'd pull apart the drive and double check the impeller/water pump. If the engine ran for even a few seconds with the outdrive on and not conected to a running hose, you could have fried the impeller. For instance, the drive is installed, and you start fine tuning the engine thinking you have water in the cooling kit to keep the engine safe for a few minutes, and forget that whenever the engine turns over, the drive shaft and impeller are moving, boom, you just fried the impeller.

Thank you for you reply. Yes the stern drive a mercruiser 888 has just been rebuilt and I installed a new impeller, impeller housing and key way. We then pulled it apart after our second run of overheating and the impeller is like new. We checked the output of the pump and it is 4 gallons per minute at 750 rpm idle. So the pump is performing quite well. We checked out the heat exchanger innards and it looks great as the unit is new. We pulled the risers off of the manifolds and they had no rust in them and are very clean. So we are moving on to engine timing next.

Thanks again, Tom

You state that you put a Volvo engine in the boat. You have gone from prehistoric manifolds to center risers I assume? You need to be sure the hoses are routed correctly as they could be confused between the thermostat housing (water distribution block) and the manifolds. Remember, water flows one way while the t-stat is closed and another after it opens. If you are using the original manifolds, be sure they are not clogged.

Regarding your volume test, reference MCM service bulletin 82-4. I believe your drive is a 1.50:1 ratio. You should get 4 gallons min @ 1000RPM. So you are good there except that the boat must be in the water, a garden hose will corrupt your reading.

If you are using the original water distribution block, check it for corrosion. Also, if your lower unit water intakes are damaged or missing (the plastic inserts if yours has them) that will cause problems at speed.

Do you really have an overheating problem or an indication problem. A bad voltage regulator will cause the indicator to read high. I doubt timing is an issue.

Thank you jmandros, yes the engine is a new Volvo Penta Ford 351w. The manifolds and risers are new as is the San Juan closed water cooling system new heat exchanger and all hoses are new. My 4 gallon reading was on a water hose. I have been using an infrared temp gun for all of my temp readings to verify the degrees in Fahrenheit. The compression on the engine is 145-150 psi across the cylinders. We check all of the hoses per the diagram and found two incorrectly installed and changed them to the proper locations. I had forgot the water pump bypass hose and installed it a couple of days ago. We have removed the thermostat for now until we nail down the problem.
We are good on the plastic screen inserts. we removed them and checked for debris and found none. We installed a clear hose form the stern pump to the heat exchanger and discovered that we are getting quite a bit of air in the hose so replacing the water pump, housing, keyway, and all gaskets an O rings to be sure that we we have no air leaks. We pressurized the upper stern drive with water and no air in the line so it has to be an issue at the pump. Thanks again for your suggestion and information.

Tom

Since the water pump in a #1 drive is situated in the exhaust area, any gasket leak could allow exhaust to be sucked into the cooling water flow. So, look at the base to lower unit gasket, base to steel plate gasket and the steel plate to cover gasket.

Because you are running closed cooling, you have a 160 deg t-stat. Remember, the temp gauge is very sensitive to voltage and the extra 13 degrees will cause the gauge to indicate higher than you would have seen with a 143 deg. What kind of readings are you actually seeing with the infrared?

Good suggestions Karma, we are going to replace the pump again with a new kit and will pull everything that requires a gasket or O-ring and replace with new. We have been seeing temperatures as high as 195 degrees many times. We are missing some little thing here with big consequences. Again Thanks, Tom

Well I finally discovered that the number 8 cylinder had a defective plug wire and has never fired. I made a new one and the first start was smokey but when that cylinder burned off the fogging oil and engine build lubricants it settled down and started running well. We also replaced the pump and the pump base. Temps are real good. We took the engine up to 3200 rpm and noted a cruise speed of 24 mph. A good speed for fuel mileage. We are still varying the speeds for the first ten hours of break-in. Glad to have it running so very well. Tom

Congrats - now thats some trouble shooting! glad it worked out!

Thanks much Karma for your suggestions. I took it out into the Columbia River here at Astoria today with my wife Joanne Marie on the boat bearing her name. It was a lovely trip and the boat ran flawlessly.

Regards, Tom

Tom, beautiful area there. The wife and I took a month off last year in June and toured. Took lots of pictures from on top of the tower, even flew a few planes
Then made the 5 day trip back to WI.