Overheating Mystery!

[johnrolf]

My 1972 Chrysler 35hp has been running perfect until last week. I took it out, got the impeller intake clogged and burned up the impeller. IT overheated really bad! Smoking like a chimney. I replaced the impeller and now it runs like crap. It seems like it is missing. It will run but it surges every couple of seconds. Don't know if it's a gas problem or what. I know that it is not and electrical issue becuase I've checked both plug wires for spark and it's all good. Plugs are good too. It had been running PERFECT before the overheat. The engine also is still overheating. The impeller and waterpump are in good shape and it seems to be pushing water very well. I also flushed the system with a water hose to check for blockages and found none. Why is it still overheating and running rough? These problems have to be in deirect relation to the bad overheat I would think.

 

[BF]

Re: Overheating Mystery!

Have you checked compression since the overheat? It is possible bad things happened... like melted rings and/or piston.

 

[eurolarva]

Re: Overheating Mystery!

That motor has a water bypass on it. So even if you see water coming out the telltale water may not be getting through the engine. Try removing the thermostat and run it without that to see if it improves performance. I dont recommend doing this as a fix but just for testing. You should first do the compression test that BF mentioned. If compression is good and removing thermostat does not help you probably have blockage in the motor. If water is coming out the telltale then the water system at the exhaust gaskets are not plugged. Your plug is probably somewhere where the thermostat is connected.

 

[johnrolf]

Re: Overheating Mystery!

Removed the thermostat and same problem. Don't have the tool to check compression, but will try to get that done. Could it possibly be that I fried the head gasket?

 

[eurolarva]

Re: Overheating Mystery!

How do the plugs look. Is one clean? I got my compression tester at sears for 30 bucks. My 1967 chrysler 45HP was blowing 145 on each cylinder last week. Yours should be well over 120. You need to test it when it is warm. Should not be a problem for you . You may want to buy a new head gasket and look inside to see if you can see anything. If water is coming out the telltale you are getting some flow it is however only cooling the exhaust area. My guess is you are not getting any cooling on the starboard side. What is the model number of this motor. I have the factory manual and the factory parts list and I believe the 35 is included in that. I dont know if that will be any help to you but let me know if it does.

 

[johnrolf]

Re: Overheating Mystery!

Model # is 354HC. Should I pull the water jacket off and take a look for obstructions? Also, the plastic adapter piece (water line seal?) that comes out of the water pump and on to the copper water tube to the small block is melted pretty bad. I'm not sure if the water line is seating in the water pump deep enough. It looked like it had enough pipe left to seat in petty good, but that might be part of the problem. Also, will a bad head gasket cause the engine to run rough, like it is missing?

 

[eurolarva]

Re: Overheating Mystery!

Here is the part number for that sleeve FA485914. Mercuty sells them for 3 dollars. Interesting. Last time my impeller went out and my motor overheated that part melted on mine as well. As long as you are getting water to the telltale I would concentrate the search after that point. Start where the water goes into the head through the thermostat. You mentioned the motor was not running very good. It sounded like it was missing. Does this happen when you first start up or after it heats up?

 

[johnrolf]

Re: Overheating Mystery!

It seems like it is missing, but I don't think it's a fire issue at all. It may be a fuel problem. It's strange because it didn't do this before the bad overheat on the lake. It did do it only at startup sometimes. I would crank it and for the first 30 seconds or so it would run rough and sound like it was surging, and then even out and run perfect. It does it constantly now though. It does it when I first crank up till the time I kill it, when the engine is cold and warm. The telltale is getting water and it looks like the normal amount of water that it usually expels. Other than a blockage in the water circulation, what else can cause an overheat?

 

[eurolarva]

Re: Overheating Mystery!

You should get that compression tester. You really need to start there. If compression is good then you need to find the blockage on the water. After that the missing. The missing could just be the timing is slightly off. I cant think of any other thing that can cause overheating other then water not flowing. Other then your pistons are damaged and they are overheating.

 

[johnrolf]

Re: Overheating Mystery!

Will any auto parts store have a compression tester? After I check for compression, what is my next step of action?<br /><br />1. If compression is good, where do I check for a blockage. What parts should I check and in what order?<br /><br />2. If compression is bad, then what course of action?

 

[scotiany]

Re: Overheating Mystery!

Even Kmart and and Sears have compression testers,. It's not a rare item.

 

[eurolarva]

Re: Overheating Mystery!

I hope someone can help you with the blockage problem. I have taken the powerhead apart only on the exhaust side (port side) of my motor. I have never had the head gasket off. I think this is where you are going to have to go. I would get another head gasket because I doubt you can remove it without damaging the old one.<br /><br />To test the compression <br /><br />You will need to either use muffs or a garbage can with water. Let motor warm up and then kill it. Remove both plugs and leave them hooked to the plug wires and ground the spark plug threads to the ground on your motor. Advance the throttle to wide open and use a clamp to engage the neutral interlock switch. let the starter turn at least four revs and write down the reading then do the other cylinder. <br /><br />When your motor overheated the first time was the impeller intact or was some of it missing? Did you hit sand or something? A word of caution. I tried removing the exhaust gaskets from my motor and three of the bolts broke. I had to remove the powerhead and drill out these holes and refill and tap with JB Weld. This stuff sucks and I dont think it will hold anywhere as good as the original threads. You may just want to do the compression test and then call around to mechanics and see if someone can help you out. You might get lucky and remove the head gasket and find the clog and be done with it. The gasket set for the entire head is 45 bucks. That includes every gasket in the powerhead. You have to decide if your mechanical abilities are up to the task. This forum is great for simple stuff or bouncing ideas around that people may not think about, however it is easy to trash a motor if you dont know what you are doing. I wish you luck.

 

[johnrolf]

Re: Overheating Mystery!

Do you know the part number for the gaskets for my engine? It's a 354HC.

 

[eurolarva]

Re: Overheating Mystery!

Original merc number for the head gasket is F201529. Original Chrysler number is 201529-1. Merc is not showing the price for the part. If you go here Head Gasket Part number 18-3856 cost 22.91 dollars and it is the same part. You may be able to get this through NAPA however they are having problems getting force and chyrsler parts.<br /><br />If you want a complete gasket set for the power head the part number is 18-4314 and cost 37.98 dollars powerhead gasket set

 

[interceptor]

Re: Overheating Mystery!

john_chrysler,<br /><br /> Your overheat sounds similar to mine (Force 50). Outboard won't run properly, but mine is now low on compression. Don't know what it was prior to overheat, but it's now down in the low 90's, which allows it to run, but only at about 1/4 throttle or so. I'm planning on just parting it out, as this seems to be a common ailment with Chrysler/Force outboards.

 

[jasonbailey]

Re: Overheating Mystery!

The head gasket sounds like the way to go. I did it on mine as well. I had an overheat problem on a 75hp. I ended up putting two gaskets in, the first time I did not have the head plained. I highly recommend taking the head to a machine shop and having it plained. If you don't you'll be buying another head gasket. Oh, and buy a new set of head bolts too.

 

[johnrolf]

Re: Overheating Mystery!

Talked to a boat mechanic and explained my problem. His 1st response was water pump problem. 2nd, he said check the head gasket.