Mercruiser 3.7 170hp overheating problem

[southwest395]

Re: Mercruiser 3.7 170hp overheating problem

and which way does the thermostat go in? Umbrella up or down towards the heat exchanger ?

 

[stonyloam]

Re: Mercruiser 3.7 170hp overheating problem

From the "book": "Install the thermostat with the umbrella up"

 

[KCKracker]

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

did you use a thermometer to see what temp it opens?

 

[southwest395]

Re: Mercruiser 3.7 170hp overheating problem

did you use a thermometer to see what temp it opens?

Thermostat opens at 160 degrees well thats what ingraved on the side of it.

 

[southwest395]

Re: Mercruiser 3.7 170hp overheating problem

Ill try a thermometer tonight thanks

 

[KCKracker]

Re: Mercruiser 3.7 170hp overheating problem

Ill try a thermometer tonight thanks

ok so now you know its a 160, so drop a thermometer in the water and see if thats when it opens

 

[ktbarrentine]

Re: Mercruiser 3.7 170hp overheating problem

Just curious....why do you have a 160 deg t-stat in there? I thought 3.7's took a 140 t-stat. Better check your book to make sure.

 

[Old Yeller Boater]

Re: Mercruiser 3.7 170hp overheating problem

According to manual, all models of the 3.7 in the 85 to 89 range use a 160. When looking for the 99155T2, that's the only ones I found.

http://boatinfo.no/lib/mercruiser/manuals/mercruiser8.html#/0

somewhere around page 243

 

[ktbarrentine]

Re: Mercruiser 3.7 170hp overheating problem

According to manual, all models of the 3.7 in the 85 to 89 range use a 160. When looking for the 99155T2, that's the only ones I found.

http://boatinfo.no/lib/mercruiser/manuals/mercruiser8.html#/0

somewhere around page 243

Excellent! Thought I saw reference to a 140 in a parts book once, but this manual spells it out clearly! Thanks!

BTW...Southwest, look at pages 251 and 252 of this manual link to get the info you need on testing/replacing your t-stat. Sounds to me by your test so far, you could use a new one.

 

[Old Yeller Boater]

Re: Mercruiser 3.7 170hp overheating problem

Have you pulled the ends off your heat exchanger to be sure there's nothing in there blocking the water flow? Mine had bits from an old impeller in it.

 

[IceWater]

Re: Mercruiser 3.7 170hp overheating problem

I have a 1980 Silverline with a 470 and I am having the same problem. I was was fishing with my wife and kids about a week ago and the boat was running fine, great, actually. We trolled for about an hour, shut down to cast for a bit and when I fired it up ago it immediately overheated. I'm taking it to the shop tomorrow as I just don't have the time to repair it myself. Hopefully I didn't cook the engine, but I don't think I did as I got it shut down quickly.

Regardless, I am learning a lot from this thread and I appreciate it.

 

[Old Yeller Boater]

Re: Mercruiser 3.7 170hp overheating problem

I have a 1980 Silverline with a 470 and I am having the same problem. I was was fishing with my wife and kids about a week ago and the boat was running fine, great, actually. We trolled for about an hour, shut down to cast for a bit and when I fired it up ago it immediately overheated. I'm taking it to the shop tomorrow as I just don't have the time to repair it myself. Hopefully I didn't cook the engine, but I don't think I did as I got it shut down quickly.

Regardless, I am learning a lot from this thread and I appreciate it.

Here's another thread that may be of help to you:
http://forums.iboats.com/showthread.php?t=561585&p=3871168#post3871168

 

[ashley4262]

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?

I had this same problem. Relaxed everything except the head gasket. There is a freeze plug on the exhaust side rear of the head. I pulled the waste water hose and hook a garden hose to run through the system. The freeze pug was rusted aeway and waste water was pouring out of the hole. Once we replaced that freeze plug our over heating problem was solved. So if your over heating and have change everything check this freeze plug before replacement of head gasket.

Hope this helps all who have this problem