F36 Overheating both engines

[pwollsch]

Hey every one, frustrated as ever... Here is my saga:

1974 Chyrsler M400's with dual helm + Sherwood D55 pumps

1. After running (under-way) for 10-15 mins both engines will reach 160 and hold
2. After no repeatable amount of time they will begin to drift to 180-200. I shut down and start the same sequence over.
3. Maintenance actions completed:
- All New impellers. Found broken vanes in both pumps from previous impellers - the ones I removed were intact! They had a set to them and were old.
- Oil and transmission coolers backwashed and checked for more debris = all ok
- Removed thermostats, tested in hot water on stove confirmed the both opened at 140-150
- Installed new Sherwood on SB engine ($$ ouch)... rebuild would not hold seal
4. While at dock, temps hold at 160 like I expect. Even running RPM's up and holding for 5 mins at 1800RPM.
5. I did notice my gauges in salon vs the flybridge are not the same readings - off by 20 degrees
6. Hoses are mostly very old, I checked for tight clamps and no air intakes

Today I am going to check resistance of senders and wiring (previous thread - great advice thanks!). I also have a portable gauge I plan to install on
one engine in place of buzzer sender on Thermostat housing to get independent reading when under-way

Any ideas?

[mikeandanne]

Hi there---- are these raw water cooled engines or fresh ?---- get yourself a hand held temp gun so you can shoot different areas to double check temps , therm housing, block, heads , oil pan etc ,I would do this before going any further----- seems odd that both engines are the same---- when you say you shut down and start the seq. over do you mean that both engines start at 160 and climb again--- if that was in a street car I would say a bad radiator or the circulation pump was tired because it will idle at temp spec all day and only goes over the edge when under load --- that said after total timing was checked----- lots of guys here with marine experience--- Mike

[Cmount]

I would actually check the thru hulls...being this late in the season, could they be clogged from the outside?

Also, how is the water flow out? you should see a real steady flow at the dock...You have done so much already, this is all I can come up with if the engines are running well.

My f32, with twin 318's does heat up under load...and goes as high as 200 if I push her at 3300...higher rpms will drive it higher.

[Big D]

I assume you replaced both impellers in each pump right? Don't laugh, or feel bad if you didn't, ran into folks that have replaced impellers and didn't know there were two in each. Yes take temp gun and confirm readings at the engines first. Old intake hoses will also fall apart inside and reduce flow. Clogged manifolds will also restrict flow. Try running with no t-stats and see what happens.

200 deg is too high Cmount.

[Cmount]

Yea im not happy when it gets there but i have new manifolds impellers etc. ill look at it again over the winter.

[8lug]

by no means am i a pro or a mechanic but
i had a set of crusaders 454's they would do the exact same thing
i even replaced most everything you did
i tried everything
finally i figured out i had air in the system
i had to let it heat up to operating temps so the system had pressure and bleed it off while it was running at different locations on risers, elbows, ect.
quick, easy, and free
the temps stabilized and ran as they should for the remanding time i owned it
you have went this far with it i wouldnt do anything else till you bled the system
o and you will know immediately if air is in there

[pwollsch]

Thanks everyone for the great comments.
I got the overheat to occur at the dock now.
I have good flow out the exhaust.
It is raw water cooled. I have no strainers, only the grates on the hull.
I suspect I have restriction there. Going for a dive today.

All new impellers...4 of them.

I used heat gun and confirmed high temps at sender and block, exhaust,
Etc.. She is overheating. Exhaust manifolds are coolest part when the rest is hot. The thermostat output going to the risers and elbows is very hot.


A very interesting comment from SLUG -- I have a friend in the marina that said the same thing. He says air gets into these systems and must be bled out. He does it first time in every spring. He connected a hose at the thermostat bypass output that normally feeds back into the cooling pump inlet. He then capped off the inlet where this hose was at the pump inlet and ran the engine for a while. I will try this too. I am not sure how to bleed air out as you describe, or this essentially what my friend is doing?

[gettaway]

I have Crusader 454 350's and when the PO had his mechanic replace the manifolds extensions and elbows at purchase, the mechanic used a vacuum type hand pump to pull air out of the cooling system, he had to bleed the cooling system several times to get the temps to run normal there is a petcock on top of the thermostat housing that he bled from as well.

Also, at least with my 454's, if I idle for a longer period of time, the temps rise, if i give enough throttle to get the RPM's at about 1000, the temps drop, due to increased water flow through the HE's. the entire cooling systems on our boat are new, from the raw and cooling system pumps, manifolds, extensions & elbows, hoses and coolant, HE's and oil coolers were sent out and cleaned.

[pwollsch]

pulled thermostats out last night and went out.... still got hot.

Weather was bad, cold.... did not want to dive in and check the through-hull grates at the intakes.

Anyone have a photo of what one of these grates looks like? (1974 F36 boat with Chrysler M400's)

I do not have strainers - just a grate before the seacock.

[gettaway]

Just curious, do you have decent water flow out the exhausts? Could you rig up a back flush to your raw water intakes and use dockside water to back flush thru the seacock , you should see bubbles and turbulence from the side of the boat in the approximate area of the seacocks.....

Risers and elbows corroded closed?
Plugged oil coolers or heat exchangers?
Calcium build up in the raw water pump causing cavitation?

[Hardeight]

I just had the same issue with my starboard motor. Last time out the belt broke and overheated the motor. I got the new belts on yesterday and took her out. Right away she heated up and I thought I had something else messed up. I let the engine cool down and checked the coolant level and topped it off, I then started the engine without the cap on and she took more coolant. Once topped off and the cap replaced she ran at perfect temp all the way to WOT and the rest of the day. I used to have to do that to my old pickup truck that had a 454..... try it out and see what happens.

[Big D]

Bill, coolant doesn't apply here,he mentioned earlier that it is a raw water cooled system.

[mikeandanne]

pulled thermostats out last night and went out.... still got hot.

Weather was bad, cold.... did not want to dive in and check the through-hull grates at the intakes.

Anyone have a photo of what one of these grates looks like? (1974 F36 boat with Chrysler M400's)

I do not have strainers - just a grate before the seacock.

http://www.4secondsflat.com/Spark_plug_reading.html
If you can, take out two plugs from each engine,one from the front and one from the back --- do not clean them or touch the electrode end-----I am curious as to why both engines have the same problem and if you would like to read the plugs( initial and total timing) check out check out 4seconds flat website- just a shot in the dark but you never know ,as it seems you have checked everything else--- I have had my boat for a year and find all kinds of wacky stuff in almost everything I have checked--- Good luck. Mike

[dfg4240]

sounds strange to me.
both engines doing the same thing tells me it is not thermostats or manifold or risers. I've heard of overheating due to timing being off but both at the same time is hard to believe.
I replaced my starboard manifold and my boat runs cool and infact running the whole way from oswego ny to the genesee river which is 55 or 60 miles at 21MPH and sometimes faster my engines never went over 120 degrees.I am going to the boat tomorrow and I will take a picture of where the intake is and what it looks like for you if you want.
too bad you could not take the intake hose off and connect it to another hose and hang it over the side and let it draw in fresh water to the engine unrestricted.
I noticed before I left the marina in seneca lake that the water had lowered a lot and there was tons of seaweed under and along side of the boat and was thinking that I better not let it sit there and idle in the slip as the seaweed would get sucked up into the intakes eventually.
dfg4240

[paskyhawk]

I have a 36 Tri that had a similar problem, I tried some of the same things as you did. I took the dock water hose and hooked it up to the raw water line going to the hull strainer, blew out what ever was caught in the hull inlet.

Rich

My wife and I put 300 hours into restoring my parents boat for them (age 88 and 90), you guys have been a great asset, Thanks.