90 hp 3 cylindar overheats at idle

[Whitefox]

I have a 90 HP Chrysler about a 1976, SN is 7682. Cruising at speed, its is fine, but if I idle it for 5+ minutes its get hot. I already replaced the impeller, and it is pumping, but at idle there is very little water coming out of the ports at the back of the motor.

The impeller that I removed was in fair shape and still had all its vanes attached. But the new impeller is pumping no better at idle then the old one did.

Before reinstalling the lower unit I ran water up the water line with a hose, and did not get much flow, but when I put the hose to the water exit port at the back of the intermediate cover, I had good flow out the water tube. I have a manual ordered, so I will check that when I get it. I suppose there could be a partial blockage in the flow tube up to the engine head.

I found in another thread information about adding a tell tale to the motor, it looks like a great idea, so next time I run it I will be removing the plug at the top of the motor to check water flow from there. If there is a partial blockage from below, I am wondering if adding the tell tale indicator would be a 'cheap fix' for the low idle flow problem.

 

[pnwboat]

Re: 90 hp 3 cylindar overheats at idle

Have you tried replacing the thermostat?

 

[Whitefox]

Re: 90 hp 3 cylindar overheats at idle

I am pretty new to the world of out board motors, and had no idea it even had one. I am ordering the manual as soon as I can make sure I find one that actually has my application in it. but until i get one, where is it located??

 

[DavidW2009]

Re: 90 hp 3 cylindar overheats at idle

Please provide the model number. It's on the tag, inside the cowl, front starboard on the motor.

Then go here to determine the year & hp.

http://www.maxrules.com/ChryslerModels/90_150.html

edit: According to the exploded drawing in the Clymer's manual, the thermostat on a three cylinder is located at the top of the cylinderhead, under a removeable cover.

 

[Whitefox]

Re: 90 hp 3 cylindar overheats at idle

The tag reads:

907HB
7682

Looks like it is a 1975 motor:


hp Year Model
90 1975 907HB

 

[DavidW2009]

Re: 90 hp 3 cylindar overheats at idle

or a 1976, 90 hp

 

[DavidW2009]

Re: 90 hp 3 cylindar overheats at idle

I need to clarify the thermostat location. My description may have been too vague.

The thermostat is located on the vertical face of the cylinderhead, the same face that has the spark plugs, at the top, just above the top spark plug.

There are (4) screws holding the cover to the head, according to Clymer's.

 

[DavidW2009]

Re: 90 hp 3 cylindar overheats at idle

I just went out and pulled the cover on my 90 HP (907HA, 1974), and it does not have the removeable thermostat cover as shown in two places in the Clymer's manual. I'm not sure how to get to the thermostat. But maybe yours does have it??

Best summon a Chrysler expert on that one. I need to know, also.

 

[Whitefox]

Re: 90 hp 3 cylindar overheats at idle

Thats OK, I don't do anything in a hurry these days. I am retired after all.

But I am pretty sure that mine is like yours. Yup, I just checked, it looks like the head needs to be removed to access the thermostat.. Interesting design.... NOT!

 

[DavidW2009]

Re: 90 hp 3 cylindar overheats at idle

I'm learning that these aftermarket manuals are not accurate in several places.

Example: In one of the exploded-view illustrations of the Tillotson carb, the float is graphically shown upside-down.

There are other examples, but I won't go there. Don't want to turn this into a product bashing thread. LOL.

 

[Whitefox]

Re: 90 hp 3 cylindar overheats at idle

Well when we are dealing with equipment that is 34 years old, OEM manuals are hard to come by. We just have th engage our brains before picking up the tools.

 

[pnwboat]

Re: 90 hp 3 cylindar overheats at idle

Boy don't I ever know that feeling! LOL! Been there, done that more times than I'd like to admit to.

 

[huskerdaninva]

Re: 90 hp 3 cylindar overheats at idle

My '69 70hp is the same set up. You have to remove the bolts from the head, including the three small ones (two if you have a thermoswitch) more towards the middle. The plugs have to come out too.Then the outer waterjacket cover comes off and voila...Mr. T-stat. I believe the Frank had mentioned something earlier about possibly switching to a later model cover style that had a separate access for the thermostat.
Dan

 

[RRitt]

Re: 90 hp 3 cylindar overheats at idle

don't forget the impeller housing. after a while they can get pitted up enough to cause this same problem. It's probably not the problem ... but I haven't seen it mentioned and this is a pretty old engine.

 

[Whitefox]

Re: 90 hp 3 cylindar overheats at idle

Yeah I looked at it, and virtually NO pits. There was 1 tiny hole in the pump housing that appears to have been put there on purpose, probably to pump fresh water into the lower end since the exhaust exits through the cavitation plate just aft of the prop. I noticed when we had the motor running also that there is a small hole through the lower unit housing on the starboard side that was expelling a small stream of water, the hole appears to have been drilled, but could be production as the paint does not look disturbed, (yes it could have been repainted). Upward and onward. I still wonder if there might be a blockage of the water exiting the engine... I am installing a tel tale out of the top of the motor, that will insure that there is circulation.

Well I have the telltale in, put water on the motor, started it, and there is not a lot of water coming our of the telltale I am really starting to thing that there is a blockage of some sort in the cooling water flow.. From the pictures I have seen on the 'telltale thread' there should be a lot more water flow then I am getting. At least it only overheats when at an extended idle, runs cool when cruising at 4,000 rpm

 

[DavidW2009]

Re: 90 hp 3 cylindar overheats at idle

Frank says that hole is for draining a blind cavity in the lower end. Mine does the same, also. Though I haven't checked it yet, I suspect the water streaming out is cold.

Here's a link to the thread with Frank's answer:

http://forums.iboats.com/showthread.php?t=378091

 

[Whitefox]

Re: 90 hp 3 cylindar overheats at idle

thanks I was hoping to get a stream like post #21 that mark posted on the telltale thread

http://forums.iboats.com/showthread.php?t=210027

go there and scrool down to post #21

My motor barely puts any water out the telltale.

 

[Whitefox]

Re: 90 hp 3 cylindar overheats at idle

OK I still do not have a manual, but I was reading something in the post about replacing the impeller that caught my interest. I think it goes along with my thread. Also, the impeller replacement thread discusses a gasket under the stainless steel plate under the impeller/water pump. Mine had no evidence of a gasket, nor was there any RTV like substances apparent. There is a very slight amount of wear on the plate from where the hub of the impeller rubs against the plate. You can see it, but not feel it, more like polished.

I will paste the portion of the instructions about installing an impeller that are not clear to me,, Not your fault,, I am just a bit confused about it.

http://forums.iboats.com/showthread.php?t=231685

Now remove the six (1/2 inch hex head) exposed mounting bolts under the cavitation plate. The lower unit may just slide right down, or it may take a little persuasion with a rubber mallet. The black rubber crankshaft seal will probably come off the top of the drive shaft as well as the steel collar. If they stay up inside the midleg, lower the engine and they should just fall out. If not, tap and jiggle a bit. When you go to replace the lower unit, the collar goes on with the groove facing up and the rubber seal goes on with the beveled end up.

The part I am not clear on is the order in which the crankshaft seal and the steel collar go on to the drive shaft during re-assembly. I am guessing that the seal goes on the shaft on top of the collar?

When I took my lower unit off, the black rubber part was half way down on the shaft, and I could not tell which way the collar was installed as it fell out of the motor when I removed the lower unit.

What does this seal, seal?? And what does it touch when the lower unit is installed? Do I have a much bigger problem since it was installed incorrectly? (I hope not)

Its obviously been installed wrong since before I got the boat. I have run it several times, and the only problem I see is overheating at idle.

 

[Whitefox]

Re: 90 hp 3 cylindar overheats at idle

Right now I am waiting for the manual to show up along with the parts i need so i can get this motor running right.might have to pull the power head.

But I have lots of reading to do before the parts get here. Lots of reading.

 

[Whitefox]

Re: 90 hp 3 cylindar overheats at idle

OK I have also subscribed to the online version of the manual, and have done quite a bit of looking around. I found that there is an additional collar that goes on the drive shaft above the rubber seal in the specs. I did not find one on my drive shaft, so I ordered a new rubber seal, and upper collar. According to the mechanic at the local boat shop, the purpose of this seal assembly is to keep water and contaminants from getting to the splines and the lower end of the opening that the shaft fits into on the power head. Makes sense. When I pull the lower unit again I will check to see if that top collar is still up on the power head. I hope not!

I have been looking for information in the online manual about pulling the power head, but so far have not been able to fine it, but will keep on looking. SO until that time, I will be focusing my efforts of checking the thermostat. AS stated earlier in this thread, my power head does not have the handy little plate for accessing the thermostat, so I will be pulling the plate the holds the spark plugs.... Right after I order a new head gasket.

Yup I sure forgot how much fun it is to own a boat!

ANY suggestions will be gladly accepted at this point.