Engine running COLD MIE 215

"I have a pair of old (ear

"I have a pair of old (early 1970's vintage) MIE 215's installed in a 23' Uniflite Sport Fisherman. The engines have always run cool. When first started they will warm up to about 140-150 and then the temp drops to 120 (I assume when the thermostat opens). After that they will run all day (starting, stopping, cruising, running hard) at 120.

Recently I replaced one seawater pump. The original pump (which I rebuilt) started making noise. I couldn't find any reason for the noise so I replaced the pump with a Jabsco pump designed to replace old Mercruiser seawater pumps. The pump is quiet, but this weekend I took the boat to the lake and that engine never warmed up. It ran at 105-110 all day.

So...several questions: 120 seems too cool for the engines to run anyway (but they run so well that I wasn't worried) 1)Is it possible that the gauges (Faria out of an old Pacemaker) don't match the senders and are giving low readings? 2)Why would replacing the seawater pump make the engine run cooler? 3)If both engines run well, should I even worry about it?

Cheers,
Kelly McCoy
West Texas"

"1. These gauges are not prec

"1. These gauges are not precision instruments. If anything is wrong the temp and oil senders may be covered with a layer of crud which you could clean off of a temp. sender. An electric oil pressure sender is just a diaphragm pressure operated potentiometer. It needs to be replaced since it has a pinhole for the oil pressure to push the diaphragm. The gauge calibration may be off slightly. However, since they are not precision analog gauges, they will not display 143 deg. but rather a range of the same which may be 139 or 145 deg. I calibrated precision analog electric gauges in the military where the pointer was adjustable. Believe me there is a big difference between general use auto/marine gauges and precision gauges.

2. It is pumping a higher volume of water because it is new and tight.

3. Your choice. I would at least consider changing both the T'stats if it has been a while since they may be opening (120 deg.) to soon."

"Kelly

120 is too cool, cha

"Kelly

120 is too cool, change your thermostat.

yes it is possible that your gauges are not compatable with the sender units.

Replacing the raw water pump you may now be lifting a much greater volume of water through the system so it will make it cooler than if the pump was failing before.

You need to worry about engine temps and readings. Running Engines that do not reach correct running temps can lead to premature wear and damage and if your gauges are not correct you can never confirm wether or not your engines are in fact at the right operating temp.

Check your gauges .

Cheers
Peter C"

"Gentlemen,

Thanks for your

"Gentlemen,

Thanks for your advice, but I still have some questions...

If the gauges may not be correct they why should I replace the thermostats? Wouldn't it make more sense to find out what the real temperature is? I know that oil pressure senders come in different resistance ranges and must be matched to the gauge. Is the same true of water temp gauges? Are senders available that match particular gauges? I have looked at lots of senders and have never seen resistance ranges (as are listed for oil pressure gauges).

The new pump did not replace an old tired pump. It replaced a freshly rebuilt pump that was noisy (for no reason that I can find). The pump in the starboard engine was rebuilt at the same time and both engines were running at exactly the same temp. The engine was running great and cooling was apparently fine before I replaced the pump. It's just that it runs much cooler now. I guess it's possible that the performance of the replacement pump is greater than the original (it isn't the same pump, it is Jabsco's universal replacement for old MIE seawater pumps). I don't think that explains why the thermostat isn't maintaining the same temp in the block.

How would you suggest confirming true block temperature if the gauges are not reliable?


Cheers,
Kelly McCoy
West Texas"

"Kelly

Your engine temps ar

"Kelly

Your engine temps are critical too the long term reliability of your engines.
Constantly too low an operating temp will kill them just as surely as to high an operating temp will.

You need to confirm your gauge readings as rather being acurate or inacurate, if they are acurate and you are running your engines constantly at 120 you will be doing damage.

You can purchase laser temp reading guns reasonably cheaply which you can point at your engine and see what temp they are running at or you can go and buy a cheap automotive gauge and just hook it up engine at a time and see what it reads.

My recomended course of action for you is to
1) confirm your engine temps as compared to gauge readings.
2) If the gauges are acurate, fit 2 new thermostats.
3) if the Gauges are inacurate, fit the matching senders to the gauges or replace both gauges and senders.

Considering that thermostats do fail and are cheap, I would just be putting a couple of new ones in anyway.

Cheers
Peter C"

"OK guys. I purchased an IR th

"OK guys. I purchased an IR thermometer and took it with me to the lake today. The stbd. engine (which has the rebuilt but original seawater pump) acted just like always. Warmed to about 140 on the gauge then dropped to 120 and stayed there all day. The IR thermometer said that the actual temperature was 165 (intake manifold next to sender, top of exhaust manifold).

The port engine (which has new Jabsco pump) only got up to about 120 on the gauge and then dropped to about 100 and stayed there. The IR thermometer said that it was actually running about 125. I know that's too cool so I need to fix it.

My plan is a new thermostat for the port engine. New senders that match the gauges so that I get more accurate temp readings. Then try it again.

I still don't understand why the new pump made the engine run colder. I understand that it might be pumping more water, but if the thermostat is working correctly wouldn't the extra water just be dumped into the risers? The thermostat should still restrict flow through the block.

By the way. The IR thermometer is great fun. I checked the temperature of all sorts of things without crawling into the engine room to feel them. The stuffing boxes are running about 90. The exhaust hoses are cool. The transmissions are running about 105. It's great to know that everything is working right. The thermometer was well worth the $25 I spent.

Thanks,
Kelly McCoy
West Texas"

Examine the T'stat housing

Examine the T'stat housing for heavy rust and mineral deposits blocking or narrowing water passageways preventing recirculating some of the hot cooling water.

"I think I've solved the m

"I think I've solved the mystery...Why would a new seawater pump cause an engine to run cooler if the thermostat is working properly?

I replaced the senders on both engines to match the gauges (Stewart Warner, not Faria as I said earlier). Now the gauges match the temps measured with the IR thermometer.

I also replaced the thermostat in the port engine (the one that was running really cool). When I pulled the old thermostat I first thought that it was stuck open. Then I realized that there were bypass ports built into the thermostat so that some water goes through even when the thermostat is closed. My guess is that when I installed a new seawater pump that was pumping more water there was enough water going through the bypass ports that the engine never warmed up.

I haven't had the boat in the lake yet (just running on the garden hose), but both warm up to about 150 F.

By the way...the thermostat for a 1972 MIE 215 is only available (from Mercury) in a kit that obviously fits many different models. If anyone needs a gasket for a thermostat housing I have a whole bag full.

Thanks for everyone's advice and help.

Cheers,
Kelly McCoy
San Angelo, TX"