Overheating

my tartan 30 heats up to over 200 degrees when motoring into
a headwind. I have replaced the raw water pump what do you recommend next?

[Don Moyer]

Here's a recent Q & A we prepared from our service and overhaul manual on basic troubleshooting for an overheating late model engine:

Q: My late model engine overheats intermittently. Is there a systematic method to start troubleshooting the cooling system?

A: Check first to see if you have a normal flow of cooling water coming out of the exhaust. A normal flow of engine cooling water will usually be sufficient to build up a head within the water lift muffler at idle to overpower the exhaust pressure, and result in a "batching" of the water out of the exhaust every second or so.

If you do not have a normal flow of water through the exhaust system and out the back of the boat, your water pump could be too weak to provide sufficient water flow; or you could have a restriction in a location that can limit the total flow of water. Examples of these restrictions include a blocked raw water through-hull, a piece of broken impeller in the elbow on the outlet of the water pump, a clogged manifold, a blockage in the inlet fitting to the exhaust system, etc.

If, on the other hand, you experience overheating while observing a normal flow of water out of the exhaust, you will have to look for a restriction that is preventing water from entering the block, and preferentially moving through the by-pass hose instead. Examples of such a restriction are a blockage within the "T" fitting, blockage in the diverter cap inside the center of the water jacket side plate, or a thermostat that is stuck in the closed position.

You can trouble shoot the extent of a blockage in this location, as well as getting some short term relief, by clamping the bypass loop partially closed with a pair of pliers or a small "C" clamp.

NOTE: The bypass loop is the hose between the "T" fitting in the center of the water jacket side plate and the inlet to the thermostat housing. The short hose on top of the head between the thermostat housing and the manifold is not part of the by-pass loop.

If the flow of cooling water out of the exhaust reduces significantly as you clamp off the by-pass hose, the restriction would be quite serious and will probably require removal of the water jacket side plate and/or or the thermostat for further inspection, cleaning, or replacement.

Don

[Jim Booth]

Mine is running hot too so I pinched the bypass hose using a small clamp over a clip type clothspin. Water flow out the back seems normal and temperature stayed below 180 while under power tied to the dock. My temperature gauge says 140 though even before the engine is run. I then did the acid flush and removed the clamp, but the temperature wanted to go too high again, so I restored the pinch. After the acid flush I poked around where I could in the thermostat area. There was still loose crud laying around so apparently water flow isn't fast enough to flush it out at normal rpm. I noticed in the pinup pictures that some have a permanently installed valve in the bypass hose. Does that tell me even engines with no blockage problems need some restriction there? Based on your experience, what's the most likely spot for blockage?

Thanks,
Jim

[jhwelch]

If your temp. gauge is reading 140 with the engine cold you may have
a defective sending unit. This happened to me once and I used
a cooking thermometer to test around the engine block. Give that
a try just to rule out the sender as being defective.

-jonathan

[Don Moyer]

Jim,

Pending the results of the check proposed by Jonathan, here's a basic guide for chasing after a restriction:

Check first to see if you have a normal flow of cooling water coming out of the exhaust. A normal flow of engine cooling water will usually be sufficient to build up a head within the water lift muffler at idle to overpower the exhaust pressure, and result in a "batching" of the water out of the exhaust every second or so.

If you do not have a normal flow of water through the exhaust system and out the back of the boat, your water pump could be too weak to provide sufficient water flow; or you could have a restriction in a location that can limit the total flow of water. Examples of these restrictions include a blocked raw water through-hull, a piece of broken impeller in the elbow on the outlet of the water pump, a clogged manifold, a blockage in the inlet fitting to the exhaust system, etc.

If, on the other hand, you experience overheating while observing a normal flow of water out of the exhaust, you will have to look for a restriction that is preventing water from entering the block, and preferentially moving through the by-pass hose instead. Examples of such a restriction are a blockage within the "T" fitting, blockage in the diverter cap inside the center of the water jacket side plate, or a thermostat that is stuck in the closed position.

You can troubleshoot the extent of a blockage in this location, as well as getting some short term relief, by clamping the bypass loop partially closed with a pair of pliers or a small "C" clamp.

NOTE: The bypass loop is the hose between the "T" fitting in the center of the water jacket side plate and the inlet to the thermostat housing. The short hose on top of the head between the thermostat housing and the manifold is not part of the by-pass loop.

If the flow of cooling water out of the exhaust reduces significantly as you clamp off the by-pass hose, the restriction would be quite serious and will probably require removal of the water jacket side plate and/or or the thermostat for further inspection, cleaning, or replacement. In the case of lesser restrictions, one of our customers was able drill an 11/32" hole through the center of the "T" fitting and tap it with 1/8" pipe threads. He was then able to connect a garden hose to pressure flush the "T" and diverter cap to restore good flow. After flushing, he installed an 1/8" pipe plug in the hole.

With respect to by-pass restrictions, a bit of added restriction can keep operating temperatures in the lower range of the thermostat specifications in cases of minor build up of crud in the block and head. In fact, in subtle cases of block and head blockage, adding a restriction to the by-pass loop will frequently result in overcooling.

However, the temperatures that you're reporting are beyond what I'd recommend remediating with restriction in the by-pass loop. I think you'll find a gauge problem or a rather serious restriction somewhere.

Don