Mercruiser 3.7 170hp overheating problem

southwest395 · Jul 7, 2012

I have a Mercruiser 3.7l 170hp 4-cyl, with an overheating problem. I have changed the impeller, the raw water hose from the outdrive and inside on the block, the heat exchanger was not getting raw water, but I pulled the hose off of the copper inlet and raw water was coming through, so that tells me that the impeller is working, however the boat motor is still overheating between 170 and 200. You can smell antifreeze through the exhaust, and it is spilling out through the overflow, is there a water pump or thermostat on these motors? The inlet hose from the heat exchanger is HOT and not just warm to the touch as I understand that it should be. I recently had two tubes plugged in the heat exchanger, there is a pinhole in one and water and anti-freeze is spraying from it, would this cause the overheating problem? Is there any way, that when you are changing the coolant and raw water hoses, that you can bleed the system?

southwest395 · Jul 8, 2012

Re: Mercruiser 3.7 170hp overheating problem

And if i correct this has a alluminum block or head. At what temp does it worp the head or block. To where you will never get it stop leaking coolant again. Just wondering cause i hear it happeneds.

southwest395 · Jul 8, 2012

Re: Mercruiser 3.7 170hp overheating problem

Please is there any 470 owners that can help

KCKracker · Jul 8, 2012

Re: Mercruiser 3.7 170hp overheating problem

if you smell antifreeze then you have a leak unless its spitting out the overflow?

check the following:
pressure test the closes system, is it leaking down? if so, where. could be the exhaust manifold into the motor, any of the exh gaskets, heat exchanger, really anywhere on the engine,

also is there a drip near the front under the pulley? if so its the pump leaking.

at any rate, anytime you have a LEAK you lower your boiling point and will overheat,

I have a 470 and id start with heat exchanger and leaks. PRESSURE TEST THAT!

southwest395 · Jul 8, 2012

Re: Mercruiser 3.7 170hp overheating problem

I had the heat exchanger serviced and repaired before. Cause coolant was leaking out the outdrive. one of the tubes that where has a pin hole leak now. Would that cause it to over heat and blow coolant out the over flow bottle. no drip under the pully and no leak under the pully

stonyloam · Jul 8, 2012

Re: Mercruiser 3.7 170hp overheating problem

Time for a compression check and a cooling system pressure check. Go to Autozone and borrow the tools. Sounds like it might be a head gasket problem. Not a bad job, just have to be careful to follow the manual exactly if it is a HG.

KCKracker · Jul 8, 2012

Re: Mercruiser 3.7 170hp overheating problem

if it is leaking anywhere it will lower the boiling point, especially a bad cap.
my concern is your smelling it out the exhaust,
how long does it take it to overheat at idle?
is the oil still clean?
have you pulled plugs to see if any cylinders are wet?
have you done a compression test?

southwest395 · Jul 8, 2012

Re: Mercruiser 3.7 170hp overheating problem

oil is clean, spark plugs are not wet

KCKracker · Jul 8, 2012

Re: Mercruiser 3.7 170hp overheating problem

if you want help you need to take the time to answer questions in completion, or nobody will take the time to ask them

southwest395 · Jul 8, 2012

Re: Mercruiser 3.7 170hp overheating problem

I checked the spark plugs and check oil. Oil is not milky and it doesnt look like a milk shake. Oil looks new just as like i did a oil change. I took pictures of what the spark plug looks like and it smell like fuel no coolant and took a picture what the heat exchanger and took a picture of the front of the pump and pulled all the hoses no crack or signs of oil and coolant mixing

.

southwest395 · Jul 8, 2012

Re: Mercruiser 3.7 170hp overheating problem

About 30 mins at idle before it gets to 185 degrees. About 20min at full open throttle.

KCKracker · Jul 8, 2012

Re: Mercruiser 3.7 170hp overheating problem

BLAM we got goooood input now! ok thats a long time. a headgasket would be fast. that sounds like lack of water flow and its slowly unable to keep it cool.

if it were me id pull the Tstat and check it on the kitchen stove, then exhaust manifold off and have it checked for cracks, leaking gasket, but mostly for being plugged up with crap, really sounds like a small leak or lack of flow on the manifold. get that sucker pressure tested off the engine!

southwest395 · Jul 8, 2012

Re: Mercruiser 3.7 170hp overheating problem

Please give me a location of where the thermostat is on the motor. I thought it would be on the front where the pump is under the three bolts and the hoseing is. but i didnt see it there.

southwest395 · Jul 8, 2012

Re: Mercruiser 3.7 170hp overheating problem

The pin hole leak isnt helping either on the heat exchanger. So that as well not helping.

stonyloam · Jul 8, 2012

Re: Mercruiser 3.7 170hp overheating problem

What year/serial number of engine?

southwest395 · Jul 8, 2012

Re: Mercruiser 3.7 170hp overheating problem

Serial number is B406239 the boat is a 1986 sea ray deville II. So i would asume the motor is a 85 or 86. If it was a bad head gasket wouldnt the coolant mix with the motor oil.

southwest395 · Jul 8, 2012

Re: Mercruiser 3.7 170hp overheating problem

Here a picture of the motor oil on a recipt.

southwest395 · Jul 8, 2012

Re: Mercruiser 3.7 170hp overheating problem

Ive pulled off every coolant hose on my motor. I didnt see any thermostat on there. Is there one suppose to be there on this motor or no? Does anyone have a location to look for it? Thanks

Eric 3.7LX Alpha 1 · Jul 8, 2012

Re: Mercruiser 3.7 170hp overheating problem

Two days ago..... there was a thread:
Thread: Mercruiser 3.7 Thermostat Question
http://forums.iboats.com/showthread.php?t=562984

There is a photo there with it!
already down to page 6 of this forum... you can tell it's summer

southwest395 · Jul 8, 2012

Re: Mercruiser 3.7 170hp overheating problem

Took thermostat out and put in a boiling pot of water it awhile to open up. And it didnt open up all the way only about 1/4 of a inch. Then took it out of the water still has not closed at all. Would this be a problem with the over heating and it blowing fluid out of the over flow bottle

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