1990 Mercruiser 3.7 with Alpha 1 Stern Drive Over heat issue

[90Avalon]

I just recently purchased a boat and took it out on the water for the first time and got out about a mile and the engine over heated and lost power so I got towed back. I replaced the impeller in the Stern Drive and figured I would replace the water pump and thermostat on the inboard. A friend and I have taken I believe all of the bolts from the front housing but can not seem to remove it. Also, is the thermostat behind the housing?

It seems as the front of the engine is not allowing the cover to come off. I have included a couple of pic that have the serial numbers for the I/O.

Any other items that I should look at which may cause overheating?

Does the impeller in the Stern Drive have anything to do with the boat over heating and loosing power?


Thx in advance as this is my first boat and looking fwd to enjoying once I can get on the water.

 

[stonyloam]

Re: 1990 Mercruiser 3.7 with Alpha 1 Stern Drive Over heat issue

OK drop the wrench and step away from the engine! Put all of the bolts back in the cover, the engine waterpump is NOT your problem. Be careful to torque the bolts back 15 ft. lb (so you don't crack the cover). Change the outdrive impeller AND pump housing (OEM Mercruiser if you can get them). Take the end off of the heat exchanger and check for junk (old impeller parts ect.). Pull the aft raw water hose off the heat exchanger and stick a garden hose in there to make sure the water flows freely out of the exhaust elbow. Do not replace the thermostat until you test the old one. As a matter of fact don't even remove the old one until you replace the outdrive impeller and test the engine on muffs. Put it in a pot of cold water and heat to about 180 F, with a thermometer, note where it starts to open (about 160) and where it is fully open (about 180). Make sure the coolant in the engine is about 50/50 automobile antifreeze Here is the manual: http://boatinfo.no/lib/mercruiser/manuals/mercruiser8.html#/248 . Since you have already overheated it you need to do a compression check and cooling system pressure check to make sure your head gasket is still OK you can borrow the tools from autozone. Good luck.

 

[stonyloam]

Re: 1990 Mercruiser 3.7 with Alpha 1 Stern Drive Over heat issue

Does the impeller in the Stern Drive have anything to do with the boat over heating and loosing power?

It is very likely that it has EVERYTHING to do with the overheating. BTW welcome to the "470 club":facepalm:

 

[southwest395]

Re: 1990 Mercruiser 3.7 with Alpha 1 Stern Drive Over heat issue

The most comon problem if it is overheating is the impeller and then check heat exchanger. If you see any coolant when you remove the from cap off. The heat exchanger has a leak. They can be repaired sometimes not. If you cant repair ir. They range any where from $500.00 to $1000.00 to replace them.

 

[southwest395]

Re: 1990 Mercruiser 3.7 with Alpha 1 Stern Drive Over heat issue

You can also check the radiator cap and make sure gasket is good on that as well. Pull your oil dipstick and check to see if its watery or kinda of milky to see if its mixing with coolant. Also check spark plugs see if they are wet. Might have a bad head gasket or sepertor gasket from exhaust and coolant. Only go to this step if theres no leaking in the heat exchanger.

 

[southwest395]

Re: 1990 Mercruiser 3.7 with Alpha 1 Stern Drive Over heat issue

Before i removed my end cap on my heat exchanger. I checked my coolant level seen coolant was low. Filled it up and noticed it was coming out of my outdrive. If it does that its your heat excahnger.

 

[90Avalon]

Re: 1990 Mercruiser 3.7 with Alpha 1 Stern Drive Over heat issue

Since I already remove the bolts from the water pump cover how do I take the cover off to replace the gasket? Is that in the manual or can you give me any tips thank you

 

[stonyloam]

Re: 1990 Mercruiser 3.7 with Alpha 1 Stern Drive Over heat issue

you are talking about #15 here right? http://www.mercruiserparts.com/Show...39469.png&inbr=908&bnbr=170&bdesc=FRONT+COVER You have to pull the rotor off the crankshaft. You can borrow a puller from autozone that will work. Reinstalling is a little harder, you need to make a spacer to put it back on. Do not pound it back on, or use the center bolt to pull it back on. You cn make a installer with a stack if greased washers and a threaded rod and nut (1/2 inch fine thread) look in the manual section 4-C.

 

[H.E.mech01]

Re: 1990 Mercruiser 3.7 with Alpha 1 Stern Drive Over heat issue

Hello I am new to the forum here I have a 1990 Welcraft eclipse with a 470 3.7l with an Alpha 1.
I have had the boat for 2 months and have done extensive work to it. Currently I am in the process of replacing the waterpump seals in the front cover. I have discovered that these seals are a common problem with the 470 engine once they have some age on them. If you are already that far you should go ahead and replace them . But also what was said in a previous responce should be listened to about testing your compression because with an aluminum block and cast Iron head these engine cannoy handle much heat without causing dammage to the head gasket. I have spent a lot of time researching this engine because I plan on having this boat for a long time to come. You have to pay very close attention to your temp when running the boat and a loss of power is a bad sign. Check your engine oil and make shure that there is no sign of water (Milky looking oil) and check your antifreeze for oil also. I am new to boating but have 15+ years experience as a Heavy Equipment Mechanic.

 

[90Avalon]

Re: 1990 Mercruiser 3.7 with Alpha 1 Stern Drive Over heat issue

I just wanted to say thx to everyone that replied with a lot of info and great suggestions. I did try to put the Stern drive back together and was running out of time do to vacation coming up and wanting to get in the water before having to store it for the winter! I took it to a service dept. and they put everything back together and are trying to use something like perma gasket I believe since there was a slight leak in the water pump housing. I am crossing my fingers due to the fact that if that does not hold tomorrow the entire engine needs to be pulled to fix the gasket that I never should have loosened and taken the bolts out of... Lesson learned..... read more about marine mechanics or get in a forum of knowledgeable people to ask questions.

Thx and will update in a week or 2 of findings.

 

[stonyloam]

Re: 1990 Mercruiser 3.7 with Alpha 1 Stern Drive Over heat issue

if that does not hold tomorrow the entire engine needs to be pulled to fix the gasket that I never should have loosened and taken the bolts out of... Lesson learned.....

It does not. If it still leaks come on back and we can help you through it. We all have to learn the hard way sometimes. Welcome to the "470 Club" :facepalm: Good luck.

 

[90Avalon]

Re: 1990 Mercruiser 3.7 with Alpha 1 Stern Drive Over heat issue

Curious as to what can be done to fix the gasket without taking the engine out.?

Thx

 

[90Avalon]

Re: 1990 Mercruiser 3.7 with Alpha 1 Stern Drive Over heat issue

Curious as to what it would take to fix the gasket if needed?

Thx

 

[H.E.mech01]

Re: 1990 Mercruiser 3.7 with Alpha 1 Stern Drive Over heat issue

The engine doesnt have to be removed. I unbolted my motor mounts put a 4x4 from one side of the boat to the other and wrapped a comealong around it and lifted the engine until I could get the balencer off the front.

 

[stonyloam]

Re: 1990 Mercruiser 3.7 with Alpha 1 Stern Drive Over heat issue

The only reason that you would have to take the engine out is if you mess up the oil pan gasket. The bottom of the front cover bolts to the oil pan and if you tear that gasket when you remove the front cover the book says the oil pan gasket has to be replaced, and the engine does have to come out for that. However if you are very careful you might be able to remove the front cover without damaging the gasket, if so a little NAPA Aviation sealant and you should be OK. If you do mess it up, then take a razor blade and cut the gasket flush with the block, remove it as intact as you can and find some gasket material that is the correct thickness and make a copy. It doesn't have to be an exact copy, the holes have to be in the right places and it must fit flush with the block. Pay particular attention to to sealing that joint when you put it back together. Remember the gasket alone is about $80 and pulling the engine will not be cheap. Anyway good luck.

 

[frankttaylor]

Re: 1990 Mercruiser 3.7 with Alpha 1 Stern Drive Over heat issue

The only reason that you would have to take the engine out is if you mess up the oil pan gasket. The bottom of the front cover bolts to the oil pan and if you tear that gasket when you remove the front cover the book says the oil pan gasket has to be replaced, and the engine does have to come out for that. However if you are very careful you might be able to remove the front cover without damaging the gasket, if so a little NAPA Aviation sealant and you should be OK. If you do mess it up, then take a razor blade and cut the gasket flush with the block, remove it as intact as you can and find some gasket material that is the correct thickness and make a copy. It doesn't have to be an exact copy, the holes have to be in the right places and it must fit flush with the block. Pay particular attention to to sealing that joint when you put it back together. Remember the gasket alone is about $80 and pulling the engine will not be cheap. Anyway good luck.

If you need a good manual to walk tyou through impeller replacement let me know. I did this twice I also learned a few tricks on how to seperate lower unit from upper unit and a few tricks on hwo to get them back together.

 

[90Avalon]

Re: 1990 Mercruiser 3.7 with Alpha 1 Stern Drive Over heat issue

I did want to let everyone know that I did get a call back and my boat is done and cost me only $276.00 to get it back together and check for leaks and temperature. I felt that was not bad considering, but if you have a manual that would be great as I will be need that when I replace the impeller next time along with any trick to put the units back together.

We are going out on august 3, to test it out on the river.

Wish me luck!

Thx

 

[frankttaylor]

Re: 1990 Mercruiser 3.7 with Alpha 1 Stern Drive Over heat issue

View attachment A1 Impeller replace.pdf

I did want to let everyone know that I did get a call back and my boat is done and cost me only $276.00 to get it back together and check for leaks and temperature. I felt that was not bad considering, but if you have a manual that would be great as I will be need that when I replace the impeller next time along with any trick to put the units back together.

We are going out on august 3, to test it out on the river.

Wish me luck!

Thx

When you seperate the lower unti it can be "stuck" to the upper unit. We used a sxcrew driver wedged between the nut on each side of the out drive and backed them out to seperate units. Puting it back together we used "C" clamps on each side and tighened each side sown simutaneously. I suggest you follow the steps and pressure test since the oil is super spendy and you don't want to do twicelike I did.

 

[90Avalon]

Re: 1990 Mercruiser 3.7 with Alpha 1 Stern Drive Over heat issue

Just wanted to let everyone know that we had our 3rd voyage this past Sunday on the lake and no issues since getting the impeller fixed and the water pump gasket sealed with perma gasket. Thx for all of the help and responses!