Normal operating temprature for Mercruiser 188/Ford 302

Can anyone tell Me what temprature The mercruiser 188's should runn at? Would they run warmer just on the earmuffs than in the water?
One engine runs at a constant 190 or so temp and the othe spikes up over 200 temp. Would like to Know what is normal.H

 

Normally have 160 deg. thermostats in them. Depending on water supply with muffs, can run hotter.
I would check thermostats.

 

Most marine engines run between 70 and 80 °C (160 and 180 °F respectively). Anything inside that range should be considered normal.
Both 190 and 200 °F are too much.
It could depend on:
- wrong temperature reading (temperature gauges are not very precise)
- faulty thermostats (you'll have to replace them)
- reduced cooling water flow (check the raw water and muffler piping for clogs of any type, like plastic bags, algae, rust or other debris)
- worn-out pump impeller (it is made of rubber which can wear with time and will loose the designed pumping capacity).

Generally, the problems related to reduced water flow can be diagnozed by the fact that water leaving the exaust pipe is very hot. Normaly the raw water temperature rise between the inlet and the outlet is not bigger than 15 °C (60 °F). Anything above that should make you suspect on waterflow, so it's either related to the pump or to the debris clogging the cooling system.

 

A mercruiser of that vintage has a 145 thermostat

 

With the engines cold check your water intake volume on each engine, it should be at least 2-3 gallons per minute, your service manual can give you the exact volume. Disconnect the water inlet hose and measure the volume in a 5 gallon bucket. If the flow is low suspect a bad impeller or clogged intake screen. Shut down the engine quickly though and then restart after reconnecting the hose. If you have good flow move on to your thermostats. You can check them but at their minimal cost it isn't worth the bother, just replace them. Then check the output volume of the engine circulating pump, some dummy might have put an automotive pump on there and the impeller could be corroded to dust. Then check the temp of the exhaust manifolds, they should not be over 180 at the water jackets. You can do this with a magnetic surface thermometer available at any kitchen supply house or go to PepBoys or such and get an infrared unit, the surface unit is more accurate as it pinpoints temp where the infrared units give you a reading of the surrounding area. Record the temps, then do the same on the risers. If one manifold is more that 10 degrees different and the riser is even hotter, suspect a clogged riser and clean or replace it. If the riser and manifold are the same temp suspect a clogged manifold, clean or replace it. If all of your flow is good then you might have a lean fuel condition causing the engine to overwhelm the cooling system. Good luck.

 

I could be as simple as a worn sending unit, which only cost a few bucks to replace. Use thermometer and check for actual temperatures at the thermostat. The other obvious things are to check the raw water impellers, circulating pump, leaks at the transom hoses, blocked intake screen, condition of the cooling passages (scale, etc.), etc. The usual culprits are worm impellers, scale build up and bad thermostats.

 

I've always wondered why marine engines are engineered to run so cool. I realize that most systems are not pressurized and you don't want salt crystalizing in a raw water cooled engine. I would have thought a freshwater cooled engine with glycol etc. could stand a bit more heat in the motor and help push condensation etc. out of the oil.

So what is it I'm not understanding since I doubt I'm right and an entire industry is going about it all wrong.