Ideas on engine running cold

[txtaz]

Hey folks,
Anyone have ideas on why a '97 350 Mag MPI would run cold?
Indications (after running):
Exhaust headers cool to the touch
STBD bank warmer that Port, Port just cold
Engine stumbles when hitting it hard from idle
Carbon residue on transom after running

Could this be a stuck open thermostat or a bad temp sensor? Also the engine temp reads 120F, all electrics are good.
Thanks,
Wes

[mattyboy]

TXTAZ,
what is the lake temp?

Matty

[txtaz]

Hi Matty,
I called the marina but they were closed today. I can't imagine it is too cold since we are here in South Texas. I would guess around 70F.
Thanks for the help.
Wes

[MOP]

I would take a shot at the T stat, also if are sure that you will not going to run it in "salt" go for a 180 stat they run better up there.

[mattyboy]

70 is pretty warm have you tried to swim in it without pain :)?? even 60 degree water is cold, my boat runs cold early in the season when the lake temps are 50 to 55 degrees then in mid season when the lake is swimmable it runs warmer.
there is still water circulating in the engine with the t stat closed and pumping around 50 to 55 degree water will cool everything down, does it go above 120?? even after a hard run then when you come off plane does it rise a little then fall back down?? my boat does that as well, what does it run temp wise on a hose???
you'll get to the bottom of this
the carbon build up is something else, running rich on a carb boat don't know can an mpi boat run rich or lean??, I had this and it was a rotor problem not enough spark
the guys might have some other ideas

Matty

[txtaz]

Matty,
The most temp I get is 120 no matter idle or hard run. No spike in temp after hard run. Same on a hose. AND no I haven't tried swimming in the lake. LOL That's still a little cool for us southern boys. I think the carbon buildup is from the ECM running in cold/warmup mode all the time. Since the headers and the intake never get too hot to touch, I'm leaning towards the thermostat. When I get the boat back from the shop I will try a thermostat change. Then maybe a sensor change. I'd have the shop do it, but they already have me for $2k for a skeg repair and a prop shaft replacement.
It looks like I'm going to have a more hands on approach with this boat. AND I thought I could get away without getting my hands dirty. WHAT was I thinking?
Thanks,
Wes

[mattyboy]

wonder, being it was a Sunshine state boat if it has a thermostat at all??
good luck

[Fish boy]

Sorry I can't help with the reason, but I might be able to help with the diagnosis. I was having a lot of cooling issues as well. Since there are so many variables throughout the cooling system, a friend suggested getting an infrared thermometer. I found one at Sears for around $60, but you may be able to find them cheaper on ebay or borrow one.

infrared from sears (http://www.sears.com/sr/javasr/product.do?vertical=TOOL&pid=03482327000&bidsite=&BV_UseBVCookie=Yes)

Point it at different parts of the engine during different types of running (under load, at idle... etc). You will be able to get a good idea what is getting cooling and if there are other parts that may not. In my case, the sender was not reading accurately, but found one head (outboard) was getting cooling while the other was getting very little. Sender did not tell me this since it was located on the cooler head.

Works really well. Showed it to my dad last night on a half consumed can of coke. Showed 77degrees on the top half of the can and 49 on the part with the liquid.

At least you will know if there are any problems with different areas of the engine, and if your gauge/sender are giving you correct and consistent numbers to work from.

Good luck,

fish

[gcarter]

Hi txtaz;
Are you boating in Canyon Reservoir?

George

[txtaz]

Phil, Sorry I missed your post earlier. Thanks for reading my mind, the temp rating was going to be my next question. We will run in fresh water only, so 180 it is. Did you get your uninstall issue resolved?
Fish, thanks for the input. I have used those types of temp gauges before and they are nice. I think I will try the thermostat first. If that doesn't work, I will definatley go your route and di.gf into it deeper. Should be easy to determine if the sensor is bad....Just point, pull trigger and compare to the gauge. I also found some stuff on the ECM diagnoses if anyone wants the link:

http://www.marinemechanic.com

Thanks again,
Wes

[txtaz]

George,
We have only had the boat in Lake Medina so far. It is about 40 miles from Canyon but a part of the same reservoir system. Water temp should be the same, but cannot find it online anywhere. If that is where you were going with that question.
Wes

[gcarter]

Not really, I just love that part of the world!
I was born in San Antonio and raised in Houston. :us-texas:
BTW, I think its the Tstat or the lack of it.

Enjoy your boat!

[gcarter]

One other thing, I used to dive in Canyon, a lot.
Even when the air temp was in the 50's, the water temp was a consistent 70-72.

George

[RedDog]

Hey folks,
Anyone have ideas on why a '97 350 Mag MPI would run cold?
Indications (after running):
Exhaust headers cool to the touch - Should Not be Hot, Maybe Warm, Probably Normal
STBD bank warmer that Port, Port just cold - Probably Normal
Carbon residue on transom after running - Probably Normal for MPI
Engine temp reads 120F, - Sounds Cold .

[txtaz]

Hey George,
Hello from the home land. We live in Boerne and really love this area except for the allergies. We are originally from the coast (Rockport) and decided to move for a change. Besides, I was getting tired of my boats rusting from the salt.
We plan on running on Canyon during the summer, but so far it looks like we are getting very busy on our schedule. TOOOOO many fun things to do. LOL We will take some pics for you when we make it out there. BTW, have you been to the marina there. Nice place and very good food. We have run out there in years past and love it.
Wes

[gcarter]

Nope, haven't been to the marina.
I always thought the hills above Canyon would be one of those wonderful places to live if you could live anywhere.
The next time I get to San Antonio, I'll look you up. I was there just last October.

George
P.S. Good luck on your upcoming marriage.

[txtaz]

RedDog,
Thanks for the input. I used to own a 454 jet boat with water injected headers and the exhaust got pretty warm. Albeit, not SS marine headers but hot to the touch. Also, the intake got hot to the touch. Then again, I went through 3 engines in that boat in 2 years.
Since this is our first Donzi, I am being very carefull and learning as much as I can to make the boat perfect and reliable. Also, the engine has low hours (54 now) and has sat quit a bit from the previous owner with no maintenance. So I want to go through everything. Plus it takes time to get to know a new boat.
Thanks again,
Wes

[txtaz]

George, Thanks for the sentiment. She is a sweetheart and I'm lucky to be with her. Absolutley, give us a call next time you are here. We will take you and yours out for a day on the boat.
Poodle, Thanks for the advice. The boat is in the shop at the moment. I will send the s/n when I get it back (probably Thurday). It is a raw system. As far as a spike I have to admit, it is a new boat to me and I have not pushed it that hard. I have hit 65mph a few short times with throttle to spare. Cruised around 40mph for 20 mins a few times. Mostly went through break in cycles to check the boat out. Thank god I did that with a prop shaft bent 3/8" and no vibrations. Otherwise the damage would be worse.
The temp may be normal as in your 22 and 18. Since the sensor is only $14 I think I'll get a new one just to be safe.
Thanks,
Wes

[MOP]

Try putting your hand on the T stat housing after a run it should be at the just uncomfortible temp, 120 will feel quite a bit cooler.

[Rootsy]

old mercs up until the 90;s used a 142* F thermostat... the GEN II series beginning sometime in the early 90's went to a 160* F t-stat... the warning system goes off at 180 and is rather annoying... :boggled:

the risers should be cool to the touch.. you should be able to lay your hand on them without issue... the t-stat housing will be at operatiing temp of the motor.. and well should feel hot to the touch.. first verify that your gauge and sender are operating correctly...

[BUIZILLA]

There is no way in hell a prop shaft bent 3/8" isn't going to be felt. Is this the same shop that just charged you 2k and then found the water pump ??????? ........i'm sure your bill will be 3k before you leave there. Just my feelings....

J

[txtaz]

Trust me, I was just as amazed as the owner, head shop mechanic and everyone else. We put the prop back on and ran it in the lake. NO VIBRATION. I was sure they had done it. But after running it, I could not tell them it wasn't that way before I brought it in. So I owned up to it.
Yeah 2K is alot for a prop shaft and skeg work. It will be the last time they work on the boat.
Wes

[ToonaFish]

infrared from sears (http://www.sears.com/sr/javasr/product.do?vertical=TOOL&pid=03482327000&bidsite=&BV_UseBVCookie=Yes)
{snip}Works really well. Showed it to my dad last night on a half consumed can of coke. Showed 77degrees on the top half of the can and 49 on the part with the liquid.

Um, can I borrow this sometime? I'd like to prove that my feet really are cold...

[txtaz]

Toona,
I'm sure you have heard this before....BUT, (from a classically trained piano dude) if you can ToonaFish can you tune a piano? With a plug wrentch and a feeler gauge? :confused: :rlol: :bighug: :party:
Wes

[Fish boy]

I'd like to prove that my feet really are cold...

Toona, I have a hard time beleiving that you get cold feet about anything... ;) ;)

[mattyboy]

Toona,
sounds like you have a T-stat problem too!,
just walk over to it and turn up the heat :) ;)

till your feet get warm
:kaioken: :biggrin.:


Matty