Mercruiser 3.7 470 overheating

[franktank11]

i am in need of some help.....i have a project boat 3.7 mercruiser 470 that is still over heating....work performed: i have replaced the head gasket and resurfaced the head, carb rebuilt, starter, fuel pump, plugs and tune up.

here is whats happening. last night i put the carb back on and fired back up (Sounded Great for lots of hard work i was happy ) and ran for a 15 mins then started to over heat at an idle so i thought i was low on coolant so i went this afternoon and picked up coolant and mixed it with water and started it back up. which leads me to my first question how much coolant should i put? fill till i see some in the resivor? i put coolant in and saw that coolant was starting to come out from where the muffs are located. not good i assume :facepalm:

so i started it and ran for 20 mins and started to overheat agian. the first 5 mins no white smoke, after 10 mins lots of white smoke, the last 5 mins some white smoke not as much though.

i have done some looking around and this leads me to believe there is something wrong with my lower unit? maybe

thanks in advance for your help

 

[stonyloam]

Re: Mercruiser 3.7 470 overheating

The reservoir should be full, and the overflow while running should go into the expansion tank. If antifreeze is coming out of the outdrive I would suspect a bad gasket between the reservoir and the exhaust manifold. You could also have a leak in the exchanger. Try pulling the aft plug on the exchanger, should be only seawater coming out. If there is any antifreeze there you probably have a leak. Need to do a cooling system pressure check, can borrow the tools from Autozone. Good luck.

 

[EddiePetty]

Re: Mercruiser 3.7 470 overheating

" ....If antifreeze is coming out of the outdrive I would suspect a bad gasket between the reservoir and the exhaust manifold......."

I really believe Stonyloam meant to say...a bad gasket between the RISER and exhaust manifold !!!

And, to ensure that you have eliminated trapped air in your cooling system, raise the bow as high as possible and fill the system with coolant. Maintain the proper level in the overflow canister and the engine will maintain the correct level in the block.

 

[stonyloam]

Re: Mercruiser 3.7 470 overheating

" ....If antifreeze is coming out of the outdrive I would suspect a bad gasket between the reservoir and the exhaust manifold......."

I really believe Stonyloam meant to say...a bad gasket between the RISER and exhaust manifold !!!

To be absolutely correct that part is called the "EXHAUST ELBOW AND RESERVIOR ASSEMBLY" which bolts to the "EXHAUST MANIFOLD ASSEMBLY" but riser is OK too LOL. Just thought it would be a little less confusing to someone that might be new at this. Agree getting the air out is important with the 470, and the gasket should be checked asap, you do not want coolant sitting in the manifold where it could leak into the cylinders.

 

[franktank11]

Re: Mercruiser 3.7 470 overheating

i figured it was going to be that....dummy me i went the cheap route and picked up gasket maker that no worky! i have ordered the gasket and another 100 bucks worth of stuff of iboats! YAY! noticed my exhaust bellow is split right down the middle so my next venture is to replace all 3 (exhaust, drive, and shifting cable) replace the t-stat. thanks for the advice once i get all work completed i will update

thanks again

 

[franktank11]

Re: Mercruiser 3.7 470 overheating

Alright guys I'm lost.....I have replaced the gasket from the riser to the exhaust I got from I boats and I put the side with the slut bow side....I filled it (with the bow up) and still coolant coming out from the lower unit, frustration its starting to set in

 

[franktank11]

Re: Mercruiser 3.7 470 overheating

Alright guys I'm lost.....I have replaced the gasket from the riser to the exhaust I got from I boats and I put the side with the slut bow side....I filled it (with the bow up) and still coolant coming out from the lower unit, frustration its starting to set in......just a thought...am I over filling it?...from the lower unit water should enter the voltage regulator right?

 

[EddiePetty]

Re: Mercruiser 3.7 470 overheating

To the best of my knowledge, there are only two places that the engine coolant and the raw water become parallel: the blank/gasket (pc. 28 of http://www.marinepartsexpress.com/M...XHAUST MANIFOLD-EXHAUST ELBOW (CAST IRON).pdf ) and the internals of the heat exchanger.
IF you are certain you have piece 28 installed properly, I would suggest that you remove the heat exchanger and have a hydrostatic test conducted to the tube bundle. (Test the shell at no more that the pressure rating of your cap and the tubes at about 10 psig).

Answering your last question: Yes, raw water is pumped directly from the impeller pump in the lower unit, thru the transom via a hose and barb forward, through the voltage regulator to the forward end of the heat exchanger. The then heated raw water leaves the exchanger's tube bundle to the exhaust riser and overboard via the idle ports and/or prop hub.

 

[franktank11]

Re: Mercruiser 3.7 470 overheating

Yes sir I installed it just like that....I feared and took off the house from the voltage regulator to the heat exchanger and coolant poured out....my assumption its that the hose from the voltage regulator side of the heat exchanger to the outlet to the exhaust elbow should be surrounded by the coolant (within the heat exchanger) and have raw water running through the coils and if coolant its pouring out one would assume a bad heat exchanger and there are holes in the coils where the raw water moves through

 

[EddiePetty]

Re: Mercruiser 3.7 470 overheating

"..... one would assume a bad heat exchanger and there are holes in the coils where the raw water moves through "

At this point, a fair assumption. If you are still in doubt, remove the forward end cap of the heat exchanger and fill the engine coolant with liquid. NO liquid should be visible from the open tube ends.

sounds like exchanger hydro time to me.

 

[franktank11]

Re: Mercruiser 3.7 470 overheating

Great news picked up another heat exchanger had it tested and good to go.....no more over heating....going to get all my hard work on the water tomorrow...wish me luck

 

[franktank11]

Re: Mercruiser 3.7 470 overheating

Update! Gotit in the water today an over heated again....didn't do it in the driveway...empty reservoir checked the oil and to my suprise milky! I have replaced the head gasket already had the head resurfaced and magna fluxed....how is the coolant mixing..cracked block?....what to do next? go on to another project? Continue with this one? Will a compression check tell me if I have a crack in the block? input is greatly appreciated

 

[EddiePetty]

Re: Mercruiser 3.7 470 overheating

"...Gotit in the water today an over heated again....didn't do it in the driveway..."

This latest development sounds like a blown head gasket (time for a compression test) as you reported lost of coolant into the oil. As the newest overheat does not develop on muffs (no-load condition) I am leaning towards an exhaust passage restriction. Remove the prop, check the foot for obstructions, remove the exhaust boot and do likewise.

Realizing you have recently replaced the head gasket and surfaced the head, you have probably not had the running time to re-torque the head. The 470 is a touchy creature in regards to overheating due primarily to the dissimilar metals between the head and block...the head gasket is the weak link. As you did not report the 'radiator' cap lifting during your exercise, I believe the cooling system relieved it's pressure via the head gasket and thus water in the oil.
Please prove me wrong with a compression test.

 

[franktank11]

Re: Mercruiser 3.7 470 overheating

You are correct sir I did not retorque the head....as for the exhaust I recently replaced all the bellows to include the exhaust. Should I be looking for anything else? where are the boots located? I am going to do a compression test soon. I guess that will be my deciding factor.

Back to the head retorquing the head....should I do that with the muffs on or on the water?

 

[Eric 3.7LX Alpha 1]

Re: Mercruiser 3.7 470 overheating

Hey Frank, read your thread from top to bottom, and didn't see anywhere that you replaced the impeller in the drive? Maybe you did and didn't mention it?

Also very important to have a good accurate temp gauge on board. Let us know how you make out with those compression numbers. The retorquing is done while the engine is off but after it gets up to temp.

Not sure what your using for a repair manual, here's the best one, the original Merc service manual for your engine and drive:
Manual #8 for your engine:
http://www.4shared.com/document/zTbCbkDD/Service_Manual_08.html

Manual #6 for the drive:
http://www.4shared.com/document/zz_5pj9o/Service_Manual_06.html

 

[franktank11]

Re: Mercruiser 3.7 470 overheating

Hey Frank, read your thread from top to bottom, and didn't see anywhere that you replaced the impeller in the drive? Maybe you did and didn't mention it?

Also very important to have a good accurate temp gauge on board. Let us know how you make out with those compression numbers. The retorquing is done while the engine is off but after it gets up to temp.

Not sure what your using for a repair manual, here's the best one, the original Merc service manual for your engine and drive:
Manual #8 for your engine:
http://www.4shared.com/document/zTbCbkDD/Service_Manual_08.html

Manual #6 for the drive:
http://www.4shared.com/document/zz_5pj9o/Service_Manual_06.html

Eric, I never replaced that out board impeller. I guess it's time to do that. I am using the mercruiser "bible" .

 

[stonyloam]

Re: Mercruiser 3.7 470 overheating

Eric, I never replaced that out board impeller. I guess it's time to do that. I am using the mercruiser "bible" .

That is probably it. It would be a good idea to replace the whole thing (impeller and housing) and then replace the impeller every couple of years from now on. If pieces of the old impeller are missing look for them in the front of the heat exchanger. Good luck.

 

[Eric 3.7LX Alpha 1]

Re: Mercruiser 3.7 470 overheating

Is sounds like you had a couple of different problems going on there, with the exchanger being one. I bet that imeller is another one helping you to overheat. There is a link in the sticky for changing the impeller, under Mercruiser info, and some pretty good youtube vids, on it if you've never done it before.