96 mercury 200 efi running hotter on starboard side

**Calvin1013** · 03-15-2019, 01:56 PM

I have this same Mercury I have been working on for a while now. It was a complete rebuild. Bored 15 over new pistons and rings and bearings. I have also rebuilt the poppet. It is running good but it is running about 20 degrees hotter on starboard head. This is while on the hose. The port head is about 143- 145 but starboard is close to 160. This is being measured with infrared thermometer. I am going to pull lower off and check impeller. What else should I look at?

**Chaz** · 03-15-2019, 03:05 PM

If you were to separate the two thermostat hoses you would see that the "lower" port side expels a pretty good stream of water, while the "higher" starboard side has to deal with any air (steam) in the system as well as overcome all other "leaks" @ idle (hose) pressure to reach the highest exit point.
Bring the RPM up a little until water starts to flow out of both sides. See if they are not the same ..

**Calvin1013** · 03-15-2019, 04:04 PM

Ok what is a good temp I should be at at say 1200 rpm. On the head or where would be the best place to measure temp. I have been measuring just below temp sensor/sender

**Chaz** · 03-16-2019, 10:00 AM

Did you check for water flow out of both sides?
Injectors cleaned?
Check to make sure ign is firing each cyl in the proper rotation?
Timing?

Use your infrared on each plug body to see if you have a "flier" or if they are all pretty consistent.
It's never going to be "perfect" bank to bank with a crude three injector driver system, but it should be a lot better than 20* difference.
If your running it for extended periods of time on the hose the exhaust will tend to heat soak the whole thing, giving you a false indication.

Thinking out loud ... after the block was bored, did the little rubber diverters get put back in between the cylinders before the motor got put back together .. ???

**Calvin1013** · 03-16-2019, 02:16 PM

I pulled thermostat housing and screwed hose into flush. Water was coming out both side but fasterout of the port side. Injectors cleaned and flowed at brucato. Timing is right. Not sure about rubber diverters. I don’t remember seeing any when I took engine apart or put back together.

**Calvin1013** · 03-16-2019, 02:23 PM

Are you talking about the rubber strip behind exhaust cover between cylinder banks? If so it is in there

**tlwjkw** · 03-16-2019, 04:19 PM

those blocks (steel holes) didn't come with diverters.....

swap tha heads ta see if it changes......

**Motv18** · 03-16-2019, 06:16 PM

Being a fresh rebuild might look at timing. If the normal water flow checks don’t pan out.

**Calvin1013** · 03-16-2019, 09:47 PM

Timing has been checked. I ran it today at about 1000 rpm and it felt cooler but was still hotter on starboard but I didn’t have thermometer today. It idles at between 700-800.