PDA

View Full Version : T-stat housing question



stillcrazy36
06-18-2010, 09:42 AM
Acquired a rebuilt 350 with headers. The T-stat housing on the engine was new but not stock Mercruiser (I changed out the OMC) Any one familiar with the difference in the housings ? The one supplied was set up for a SINGLE feed to the manifold header and used a bypass plate to supply water to the riser elbow. Eddie Marine's suggested piping is to use the "jumper" hose between the two.In any case I am getting overheating.
I have replaced the raw water pump, checked the oil cooler for clogging, tested the thermostat, run it directly on a hose, all to no avail. I am now questioning the T-stat housing and the internal porting that might be restricting the flow and be sized for some other app.
At the cost of a new housing $200-400 I would like to confirm. Attached pics. Anyone have a comment on the two.

fogducker III
06-18-2010, 09:55 AM
I have the exact housing as in your first pic on my Scorpion, I have had no issues with temp........I think you might have another issue that is causing the over heating......what tempatures are you getting and where? Block, manifolds, risers, one side or both...?

VetteLT193
06-18-2010, 10:22 AM
is the water flowing out the exhaust? if so, how does it look flow wise?

what temps, what drive / raw water pump are you using? Is the circulating pump new?

Cuda
06-18-2010, 04:28 PM
It must be in the plumbing. Call Eddie Marine, they were very helpful when I got some manifolds from them. I think they had left out a brass elbow I needed.

mrfixxall
06-18-2010, 05:58 PM
1 st make sure you are putting the thermostat in the rite spot..in the t-stat housing and not in the intake manifold..if you only have 1 water port per exhaust ,maniforl which should be at the bottom running another hose to it is not going to make it not over heat..i suggest to get a old thermostat and gut the center,put it back together and run it and see it if gets hot..

if it still over heats then your problem exists elae where like a bad head gasket..


your old thermostat housing? is it stainless and if your not going to use it want to sell it :)

stillcrazy36
06-20-2010, 08:42 AM
Wow, Thanks guys for all the suggestions. When you get going round and round on one of these problems it is easy to get frustrated especially if you have crossed off something on your list.
Here is some basic info:
The motor first overheated on the lift, in the water@ 1000-1200 rpm. Reving did not help. It was at 160 for a short time and then went up to 200 and I shut it down. Risers felt uncomfortably warm to touch. I did not have time to digitally confirm.I then replaced the impeller on the raw water pump ( it looked OK) but I did not reinstall it for several months as I found other problems on that test. Oil leaks, carb needed rebuild fuel problem, the new (?) alternator was drainning the batteries, and the list goes on. but back to the OH problem.
I took apart and inspected every thing in line with the water supply system up to the motor including the T-Stat hsg and tested the T-Stat. Everything was clear. No chunks of anything. Checked the timing and was 8 degrees BTDC. I checked the Temperature sender to confirm it's reading.
I believe it is still LOW water flow to the motor so I am going to look at the pump again.
Thanks Fogducker lll-If the Tstat hsg. works for you it must supply enough for me.
VetteLT193- Removed and inspected the re-circ pump yesterday as it was questionable that the rebuilder had used a marine part. It was OK and stainless.
Cuda- already talked to EMI. Added the suggested jumper hose. Did not help.
Mr Fixall-Tstat is correctly installed. BUT I will check the head for a crack as the previous owner had a problem.
Hope I have covered everyones questions.

Cuda
06-20-2010, 11:10 AM
If you have the heads off, you can check them for flatness with a straight edge and feeler guages.

stillcrazy36
06-27-2010, 10:27 AM
Thanks Cuda. I have already rebuilt a 350 when I was younger but a cracked gasket or head is going to be my last resort. I am still stuck on not seeing enough water flow. That is why I questioned the T-Stat housing in the first place. I pulled the raw water pump again and it looks OK but I will replace it since it is apart.
Water Flow path

Pickup
Pump
Tube
Hose
Fitting
Hose
Cooler
Hose
T-Stat hsg.
Circ pump& Manifold & discharge
Motor
T-Stat hsg.
Thermostat
Discharge
I have inspected # 2,4,6,7,8,9,10, and 13

MOP
06-27-2010, 03:54 PM
Say what you like I over the years learned to hate that housing, the ball spring tension and the balls sticking have caused many an over heat. There are much better straight forward ones that have no moving parts. That being said are you 100% sure that the impeller is in the housing correctly, I screwed up myself this spring after 40 some odd years of doing pumps. I did the pump over on mine and somehow flipped two blades of the impeller the wrong way when I shoved it in, it is a crank mounted pump you can give it a twist in the right direction for the first little bit. It is hard to see if the impeller slipped in correctly. It did not over heat I just noticed that at idle I had low water flow, I pulled the pumps cover thinking that may have happened and sure enough I had two flipped. One or two blades flipped the wrong way reduces capacity big time.

MOP
06-27-2010, 03:57 PM
If the balls are not nice and round on the contact side unscrew the nut on one side pull the shaft and turn the balls so the good side is toward the housing. There should only be light tension on the balls when seated!

stillcrazy36
06-28-2010, 07:51 PM
If the balls are not nice and round on the contact side unscrew the nut on one side pull the shaft and turn the balls so the good side is toward the housing. There should only be light tension on the balls when seated!
The first picture shows the T-stat hsg. that is installed on the motor. It does not have any "Balls". It uses orifices cast in to direct the water flow until the T-stat opens. Fogduckerlll says he is using the same hsg. with no trouble but I am still not sure until I find something else.
Today I replaced the Raw water pump but again the Impeller blades were all curved in the right direction and looked good as new. I examined the pick up and verified that it is clear.
I'm still looking.

MOP
06-29-2010, 06:56 AM
I went off on the ball type housing as I hate them, they cost from Merc $500 and are crap! The one you have is a good piece and trouble free.

Now back to thoughts of your issue, get a hunk of clear hose the size needed to go from the Tstat housing to the exhaust. Take the hatch off and get a buddy to go for a ride, watch the clear hose carefully. You will be looking for a stream of air bubble usually quite small but steady, if you do see them you are sucking air into the system which collects in the cylinder heads and causes over heating. No bubbles no problem keep looking!!!!

Phil

Cuda
06-29-2010, 08:15 AM
I think I have three t-stat housings in the garage, but I think they are all from an HP 500.

stillcrazy36
06-30-2010, 09:25 AM
I went off on the ball type housing as I hate them, they cost from Merc $500 and are crap! The one you have is a good piece and trouble free.

Now back to thoughts of your issue, get a hunk of clear hose the size needed to go from the Tstat housing to the exhaust. Take the hatch off and get a buddy to go for a ride, watch the clear hose carefully. You will be looking for a stream of air bubble usually quite small but steady, if you do see them you are sucking air into the system which collects in the cylinder heads and causes over heating. No bubbles no problem keep looking!!!!

Phil
Hey thanks for a fresh idea. This problem starts at the dock, I don't even have to be up and running. I'm still stuck on water flow. Yesterday I installed a NEW water pump,checked the pick up again,Back flushed to the pump from the cooler inlet,flushed forward from cooler thru Tstat,motor,headers and out the exhaust. Good flow. That verifies #1-6. Everything appears clear.

stillcrazy36
07-11-2010, 10:32 AM
Hi guys,
Several days of rain but I squeezed in a few days of time in the Keys. I have since drilled and taped the T-stat housing for a gauge. I have never seen any stats on what the pressure should be, but I will record it for giggles. i also researched and found ( unconfirmed) that Merc says 10-15 gallons per minute @ 1000 rpm. It looked more like 1-2 GPM during my test. Hope to run new pump and gauge soon.

Conquistador_del_mar
07-11-2010, 10:47 AM
Just throwing out a possible suspect. Are you sure you have the correct direction recirculating pump? A serpentine belt driven system uses the opposite direction pump from the conventional belt driven system. Bill

stillcrazy36
08-21-2010, 09:28 AM
Long time between posts,and still crazy with demands on me. Went to try a complete new water pump and found that the drive had a oil leak on propeller shaft carrier. I got estimates on repair to do it myself and from a repair shop. It didn't look bad to me but they advised to replace it. So it's been decision time and I decided to go for a replacement drive.I bought it direct, not thru a repair shop.
This should be interesting since everything will be new.....except the T-Stat housing.