The plastic hold down spacer is a pain to get out but the trick is to use a small 2 finger gear puller and hook it to the t-stat, It will pull up both at the same time.

8 out 10 times it saves the plastic hold down spacer, # 6 in your parts list.

I am gonna rip it apart again and check it out.

The only thing I forgot to mention is before I get back to the dock (7min idle) the temp is back to 160* and everything is normal again before the boat is docked. But it happens everytime I use the boat......... could almost set my watch to it. Some have told me not to worry about it but since it has been happening I seem to get more condensation in the breathers and under the oil fill caps. It never did it before so something is wrong. The port side motor doesn't do it.

Thanks anymore input would be appreciated

These are what are called Gremlins!!!-- Don't ask where they come from but as sure as God made little green apples they always appear. I have the voltage meter on mine that requires (every year) to take the connector wires off the post- scuff them up a little and then re-attach -- or else the volt meter will peg at 18 volts.

Ground issues are in my opinion the cause of most of these problems.

all the best

3poinstar

I will echo what SB and BUP have said. I am fairly confident this is not an electrical issue but a mechanical one involving the thermostat, housing and or plastic insert. Also check for an errant piece of debris that may be in the housing perhaps missed before.

Replaced the Thermo housing and thermostat with all new senders ............. still does the same thing. I even changed the sea water pump and made sure the circ pump was working. Everything checks out, any other ideas? I am getting milk in my breathers (not on the dipstick and barley under the fill cap) which I think is a condensation issue....... possibly caused by the water temp dropping under 100 after coming off plane??

Any help is appreciated

Did you ever mention what app you have (motor) and year model along with is this a stock set up. Is your oil cooler stock set up,


What t- stat did you buy and installed ? Also did you install the correct spacer to hold down the t-stat in the housing / they have 2 different ones FYI. talking about # 6 in the parts that SB posted.

When you bought your parts did you use your engine serial # to get the correct parts for your app ? Do you have the correct t-stat housing installed per your app ? Did you install the T-stat correctly and used a new corked gasket or what ever is called for per your app to seal the t-stat in the housing ?

next just wondering what Exhaust system do you have ? If Mercruiser stock do you have the correct riser gaskets installed ?

It's a Mark 4 540. Oil cooler is stock merc 502 cooler. It's not a new build I have been running it for years.......just a new problem. I just swapped the housings from the port side to the starboard side. I am running EMI exhaust.