Thermostat OK but still running hot

[Baltimore Sailor]

Here's something I don't get: my thermostat is opening OK (tested in pan of hot water), and the housing is in good shape (meaning that the opening thermostat has a good seat on the bypass inlet to push against), but if I don't partially clamp the bypass hose with vice grips the engine will run hot.

If I completely close the bypass hose with the grips the engine runs very cool -- around 135 deg. I've "calibrated" my vice grips so that the engine runs at around 165 deg all day long, but I'm still puzzled. If the thermostat is opening properly and pressing strongly against the bypass inlet, why is that any less effective in sending the water into the block than putting the vice grips on the bypass hose?

I don't see how a blockage in the cooling jacket passages would cause this to happen. If someone can explain this I'd really appreciate it.

Thanks!

[High Hopes]

Balt,

Good question. Is it possible that the vise grips are stronger than the thermostat top pushing against the thermostat housing top? Maybe it is a matter of degree. I imagine you inspected everything when you popped the thermostat. Very strage indeed.

In mysteries like this I try to get more data. You might want to test assumptions. Unhook the water connections to the exhaust manifold and see if a glass of water flows freely through it.

Remove the hose to the water pump. Remove the temperature sending unit and rig something see if water will flow easily from the port to the water jacket tee fitting and out the hose.

Use a garden hose to forcibly back flush and see it anything comes out.

OH! Make sure your thermostat housing isn't on backwards. The housing is NOT reversible. If backwards, when the engine heats up, the port to the exhaust manifold will close. I am talking about the thermostat cover, not the thermostat itself.

Something is being assumed about your situation which is inaccurate.

Good luck. Keep us posted.

Steve

[alleytm]

Similar Thermostat Problem

Sounds like we may be having similar problems.

I have a 1965 Atomic 4 engine with the "Dole" style of thermostat and housing. The old thermostat failed a while back and this year I decided to replace the unit to see if I couldn't get the engine running at a more optimal temperature.

With the new thermostat in place, I stopped seeing water come out of the engine exhaust and the engine got very hot in a short period of time. An IR thermometer showed 219F head temperature around the spark plugs and this was confirmed by being able to boil water on it in short order.

I checked the new thermostat in a pan of hot water and confirmed that it was working properly. It opens at 140F and is fully open at around 160-180F.

I checked the water pump and I am getting a good flow of water from it.

So I fired up the electric bilge pump and started walking down the system with the engine running. With nothing connected to the discharge lines from the thermostat housing, I got a good stream of water from the recirculating (bypass) side with a cold engine.

Hooking up the recirculating line, the engine warmed up to around 175F (per the IR thermometer pointed to the top of the exhaust manifold casting) and then stayed there. The thermostat opened up and I got a good flow of water coming out of the output (i.e., non-recirculating) port of the thermostat housing.

Next, I connected the hot water tank and fired up the engine. Again, a good flow of water from the water heater core and the engine temperature stayed steady.

I then hooked up the exhaust pipe (a double walled copper pipe that carries the cooling water as a jacket until just prior to it exiting the boat). No flow out the exhaust and the engine quickly heated to over 200F.

I was able to confirm that there was no blockage in the exhaust line jacket, so I wondered if back-pressure on the cooling water flow was an issue since there is about a 30-36" lift required to pump the cooling water from the boat. To test this, I connected a 6-ft hose to the output port of the thermostat housing and started the engine. I got good flow until I raised the hose up. With about 18-20" of head/back pressure on the output port, the flow stopped and the engine started to heat up very quickly.

I examined the new thermostat more closely and compared it with the original unit that I removed. It appears to me that the new unit (from Westerbeke, according to the packaging) allows more water to "blow by" the body of the thermostat even when it opens up and seats a plunger on the bypass line. The size of the opening to allow the "blow by" appears to be enough that when presented with more than 18-20 inches of water in back pressure, the cooling water will prefer to flow through the recirculating loop around the engine regardless of the thermostat position.

My first thought was to put a valve in line with the recirculating loop to create more of a restriction so that the cooling water would prefer to flow through the exhaust system when the thermostat opened. Then it occurred to me that this simply amounted to replacing an automatic thermostat with a manual one and I decided not to pursue it further. Some of the posts on this forum have people doing similar things by clamping onto the recirculating hose with vice grips or finding some other ways to restrict the recirculating water flow.

Looking at the replacement thermostat, the bottom of the plunger that blocks off the recirculating line when the engine reaches operating temperature has about a 5/16-inch hole in it. The old unit had a very small hole -- less than 1/16-inches in diameter. My first thought was to solder a small copper or brass disk onto the end of this thermostat and, if needed, drill a very small hole in it to allow air/pressure to bleed off from the resulting cavity. I'm concerned about damaging a $50 thermostat by doing this, however.

Again, I thought I would see if anyone here had any experience with this before trying to engineer my own solution. Any suggestions would be appreciated.

Thanks in advance for your time. My apologies for such a long posting.

Tom
Alberg 35 "Tomfoolery"

[Baltimore Sailor]

You're having slightly different problems than I am, since I always get water flow out of the exhaust, even when running hot.

I installed a ballcock valve between the t-fitting and the thermostat, adjusted it to where my temp gauge reads between 170-180, and left it. No further adjustments have been needed. IIRC, this solution was actually recommended by Universal, so I don't feel badly about having it in place. When I get time I'm going to flush the engine and see if that solves the problem; but I really don't mind having a means to manually force all the water through the engine if I want to.

Hope you find a solution you're happy with!

[Don Moyer]

Tom,

I've been stewing over this report ever since first seeing it last week, and I don't believe I can resolve the issue until we do some testing of our own.

We have known for many years that variations in back pressure can cause preferential flow within the circulating loop of early model cooling systems. This tendency can become very problematic when relying totally on a manual valve to control the re-circulating loop; e.g., the valve can be set for a stable temperature at one power setting, but overheating can occur at another power setting - perhaps even a lower setting.

By being able to virtually close off the re-circulating loop, a Dole thermostat should be able to automatically adjust to these varying back pressure conditions.

In the meantime, could you please clarify two points for me? Does your new thermostat have two weep holes in the mounting flange, and are these the holes which you are referring to in terms of "blow-by" of water through the body of the thermostat? These bleed holes are intended to allow enough water to flow through the body of the thermostat to cool the exhaust while the engine is still cold (recirculating port full open and the outlet to the exhaust full closed, except for the weep holes).

Also, did you mean to say that you're seeing no water at all out the back of the boat? I'm wondering why you wouldn't at least see some water from the weep holes. In worst cases, an early model engine might create a little steam in the first few minutes of running before the engine warms and the thermostat repositions, but I'm not sure why you would report seeing nothing.

Don