Logo

1976 Chrysler 75HP failed water pump after fine day at lake?

Hippofox

New member
New to the forum, so hello to everyone here.

I have a 1976 Chrysler 75HP that I think has quite a few hours on it during it's life, but I've only got about 10 hours since I bought the boat late last fall (we got out late this year for non-boating reasons). This past week we made three trips to the lake (Beaver in NWA) and had about 4 hours of fun with no issues I could detect. Motor is pushing a 16' VIP and was doing about 35mph at top end with two people, then about 32mph with the boat fully loaded (7 people and stuff). I don't keep it at full throttle for very long though.

After about 2.5 hours of continual use (cruising and pulling a tube) the motor wasn't hot at all - I could hold my hand on the head shortly after stopping. Next day I went to flush the motor and clean up the boat. After about 30 seconds the motor started running rough so I went to 'up the pressure' on the whiskers to increase water flow thinking it wasn't getting enough water when the overheat buzzer went off (at 180F on this motor I think). So I raced back to the boat and shut it down after about 20 seconds of buzzing). There was oil on the head below the top two spark plugs that I didn't see before this happened - can't see any damage to the head.

Is this normal for a cooling system to suddenly fail after being fine the previous day? The guy I bought the boat from had the impeller replaced the year before he sold it to me and said it didn't have many hours (<25) on it. Also should I worry the motor is in any other trouble other than needing a new water pump kit installed? Or is something else likely?

I already know I have to replace the propeller shaft seal as I noticed it leaking as well, so I'm concerned about ever increasing costs. At this point I'm hoping I can do all the needed work to save on the repair, but I don't want to start totally rebuilding a 2-stroke motor as I've only worked on land loving 4 strokes!

Any help and guidance is greatly appreciated.
 
I would do a compression test with plugs out first before water pump replacement,This engine is 40.proceed from there.troubleshooting does not cost much.
 
Last edited:
Tach and stuff 001.jpgTach and stuff 002.jpg

The muffs you used might be the problem??
The muffs with the big round flat thing might be the problem.
The pics are the suggested muffs.
Also if you only had the water on slow flow that could hurt it too.
While it's in the water it has access to MILLIONS of gallons.
On the hose maybe 3-4 gal a min.

These with the small slits on the upper section need to be DEEEEEP in a bucket at least 3-4 inches over the joint where the lower unit meets the mid section.

The pump is NOT self priming.
It will pick up water and work once it's been deep enough to pick up water.

Do the compression test.
Change the impeller.
A used car/boat salesman will tell you ANYTHING to sell!!!!
They should be changed every 2-3 years with light use.
They can "take a set" and be less effective.

Oh yea, WELCOME!!
You can learn a lot from the guys on here.
 
Last edited:
Thank you both for your quick replies!

Update: Checked compression today. Pulled plugs (see image)Cob75HP-plugs.jpg they are #1 #2 #3 (top to bottom) respectively. One bit of good news (maybe) is the top plug was actually a bit loose in the head! Guess there was resistance when I replaced the plugs and I didn't torque it hard enough and it managed to vibrate loose during the long day at the lake. I think that explains the oil on the outside of the head and the foul nature of plug #1!

Comp numbers (removed all three plugs and grounded them against the head, screwed in compression tester and turned over motor about 5 or 6 times each time):

#1 - 135psi (throttle closed), 142psi (WOT - in neutral)
#2 - 141psi 150psi
#3 - 135psi 140psi

- can't find the OEM specs for compression in the manual. Maybe 150 - 160psi? Is the 10psi difference something to worry about?

Might need a new prop too as I just noticed the old one is pretty nicked up and has a small dent on one blade!
 
Last edited:
Below are some pics of the boat and the MOPAR (HaHa!) outboard.

Jerryjerry05 you are so right about people selling used (read that old ;)) stuff telling you tales, but this time I think the guy was shooting me straight (long story). I got the impression he was the type to pay for the work, rather than attempt it himself, but tell the MECH to get him out CHEAP (which is always a bad idea in my experience). Maybe that explains the early departure of the impeller (AM instead of OEM)?

Thanks again for your help / guidance - trust me when I say that I will probably repeat this many times as I'm so completely NEW to boat owning, but I've always loved and felt at home on the water.

BTW - Is 35mph a good speed for this boat/motor combo? Should it be faster?
smVal1.jpgsmVal2.jpgsmVal3.jpg
 
The comp readings are good.
IF??? all the holes are within 5# of each other it's good.
The readings could be?? Should be???
The book doesn't always post a comp # as the difference between the gauges will have someone rebuilding a head un-necessarily
As long as the readings are close to each other it will work.

A cheap gauge might read 120 on all 3 and a better gauge might read 145.
But being close is what matters.
Now if the gauge reads 80 on all?? Then another gauge is needed to make sure.

35 for your boat is good.
Here are 2 links for some good reading on repairing the Chryslers.

http://forums.iboats.com/forum/engi...ler-outboards/616464-carb-and-timing-tutorial

http://forums.iboats.com/forum/engi...orce-chrysler-faq-and-other-great-information

The links cover impeller replacement and carb setup.

Keep asking questions.
 
Back
Top