T-Stat ?
 

I have 532 ci BBC, Bowtie blocks and Dart Iron Eagle heads, I'm running a 160 degree Eickert high flow stat, factory merc t-stat housing, circulating pump, oil cooler, Stainless Marine exhaust. First time out and I could build enough heat in the engines to open the stat. According to the gauge ...140 degrees, I shot a hand held stat at the intake manifold right below the t-stat housing and it only read 127 degrees. Being that the stat wasn't open water pressure was high. I'm planning on installing water pressure bypasses but I'm not sure what to do with the stat....should I run a 140 degree stat?
Lake water temp was 55 degrees. Any suggestions???

I would keep the 160 stat as it is better for the oil and the cylinder walls. Getting the cooling system to funtion can be a bit tricky. You don't say which Merc thermostat housing you are using. They have different styles of bypasses in them and in some there is no bypass at all. Further, Merc has an external bypass valve that is used on faster boats in order to drop some of the pressure created by the ram effect on the drive.

With more details I can give you more specific suggestions.

install the bypass valves first then see where your at..when using the reytec gun you have to be rite on the intake,,the further your away from reading the object the power the tenps are..could be up to 10-20 * lower then what it should be..

I figured I would post a pic ....easier than describing. I have a "Y" fitting installed joining the two 1" hoses together before it feeds the bottom of the exhaust manifold. Bypass hose between the intake and the water pump also.

Very simple and clean setup! I'm assuming the bypass hose you speak of "between the intake and the water pump" is really the by-pass between the intake and the circulating pump. Is this correct?

On the port side of the starboard engine (pic 1), there is a small blue hose. Where is it coming from and where is it going to?

Those t-stat housings have a built in by-pass. I am guessing that you have a larger than stock sea pump and it is putting out too much water for the by-pass to handle. Some versions of these housings used plastic, spring loaded balls in the upper, forward outlet ports. These balls frequently get stuck in the ports. Are you running with these check balls in place?

Do you know how much pressure you have anywhere in the cooling system? If you have much more than 13 psi under the stat or 3 at the inlet of the circulating pump, then you have too much water trying to enter the cooling system. This can also cause water to leak out the back cover of the stock big block circulating pump.

IF this is the case, there are two ways to fix it. The easiest is to do what MrFixxAll said and add the Merc Hi-Perf external by-pass valve. If your cooling temp spikes after a hard run, then the internal by-pass in the housing will need to be reduced or plugged off. There are various springs available for this relief valve to adjust when it opens. It is also used on the closed cooled versions of the 3.0 liter, V6, and small blocks.

The second would be to open up the internal by-pass passage in the t-stat housing. This will require some trial and error to get it correct. This method will allow for a temperature spike after a hard run as much of the water will now be by-passing at idle. This is typically not an issue, but some people get nervous about it. On some versions of this housing there is a large pipe plug un the underside of the casting. Removing this plug will allow access to the by-pass hole.

Yes, bypass hose goes from front of intake to circulating pump.

Blue hose in the top of the manifold feeds the water pressure gauge.

The springs and check balls have been removed

According to the water pressure gauge as soon as I throttled up the pressure started to climb...15 lbs....I backed off the throttles then.

My housings don't have any plugs in the bottom of them and I'm using the stock merc sea pump, plastic housing.

I do plan on installing the bypass relief valves, still curious why the engines won't get up to 160 degrees. I will recheck with the temp gun and make sure that I'm close to the surface.

Sorry! I was referring to the other blue hose in the same picture.

15 psi in the water crossover is way too much and is sufficient to blow the thermostat open.

fixx
 

change the thermostat housings,,i went through this with a set of emi's..whats happening instead of all the bypass water is not going through to exhaust..whyle the thermostat is waiting to open its back feeding through the hose and the circulation pump is recirculating the water through the block to keep the tstat closed...(where the check balls and springs that were removed) thease balls should not have been removed,,thease keep equap water pressure going to both manifolds and keep water from backing through the system.

you have 3 options,,factory merc 4 port housing's,stainless marines(i have 2 new ones that they dont show on their website which im using) or the SS sierra makes which would work perfect on your's..

i blew up your picture and the fittings you have are not y fittings,,those wont blend the water so well,if anything it will cause air bubbles..

When you say better for the oil can you elaborate more. I have twin 454/425's and one motor reads 130 and the othe reads 160 when hot. I've been experiencing some issues with the motor running 130. Oil pres drops real low when I idle down, notice some soot out of the exhaust and the motor lags behind the other motor. There is no crossover installed. Could I have a 130 stat or could it be stuck open?

I would be more inclined to think the stat is not shutting. Is the temp of 130 all of the time or just at high or low speed? If you change the oil on the 130 engine, does the oil pressure come back up? If the block is running 130, then the oil is also running too cold. When that happens, the oil never gets a chance to warm up the condensation (water and fuel) and push it our the crankcase vent system.

This will also affect the fueling system. Both carburetor and EFI (but worse with EFI) will not run properly if the heads are too cold.

Are the engines running cold all of the time or at idle or at full speed?

If you are interested in trying something, you can install a T fitting on the hose that feeds water to the housing (from the cooler). From this T, place a quarter turn valve. After the valve, place another T. Run both sides of the second T to more Ts placed in the hoses coming from the upper fitting of the T stat housing. With the valve closed, you will be running like it is now. With the valve open, you will be able emulate a larger bypass in the housing or the HiPerf by-pass valve. If you like the results you see, you can go from there.

It's running 130 all the time. It warms up to 130 and stays there. I usually only run the boat up to 3k and it stays at 130. I tried going higher rpms on Saturday for a few secs and came back down to 3k. The I felt a loss of power on that motor and the rpms dropped, so I backed her down to idle speeds and that's when the oil pressure dropped to about 10 psi. I shut it off and fired it back up a couple mins later and had good pressure but when I got to PIB it was low again at idle speeds.

Should I go and get a 160 stat.

I'm assuming that the system use to run at 160 with no issues. If so, then yes, changing the stat is a cheap and simple thing to try.

The motor has always lagged behind the other and the oil pres has always been questionable along with water temp. I bought the boat last year and it came with auto meter pro comp marine gauges but same sending units. I had a mech swap the water temp sending unit last summer and since then it been 130 one side and 160 the other. Another mech told me that my oil pres was just backwards, so this summer when I notice the pres getting close to 80 I installed a mechanical gauge and that's when I notice the pres dropping to 10 at idle speeds. So I have know clue what stat is in that motor. I'm going to pick a 160 stat up tonight and then prob swap leads going to the sending units and see if the temps swap on the gauges.

I've had the 130 temp motor out for a trans rebuild and one head pulled off to tap out a broken spark plug. I plan on getting new gauges because I don't want to get knew sending units plus I'm not a fan of auto meter for marine use.