Temp guage reads 200-220 '90 SN 351 but motor not hot???

[MiracleDriver]

when we fired it up for the first time this year after winter storage (removed all drain plugs, water seperator, fogged, etc...) put everything back together and started it with the garden hose as we always do it ran fine, but the temp was up to 140 in a minute or 2 - we only ran it for a few minutes to make sure it started. Then we dropped it in the lake and noticed the temp was running between 200-220. we are getting normal water pressure and the motor was not any hotter than usual, if not cooler.

We ran it for about 1 hour and then back to the trailer when the temp light came on, although it was still reading 200-220.

the top of the water pump where it leads to the manifolds was cold to touch (running in 55-60 degree water)and as stated neither the motor nor the manifolds were that hot.

any thoughts on how to diagnose the problem?

[MiracleDriver]

haven't gotten a reply yet.. not sure if I was unclear..

I have yet to check the pump, but will do that first. any suggestions?

anyone have any diagram's on how to change the thermostat or pump internals?

thx

[WakeSlayer]

bad gauge?

[MiracleDriver]

it easily could be, I've had other electrical issues.. the boat was just in teh shop in september for a complete once over as we were having a lot of issues. they looked at everything from the compression, rebuilt the carb and installed a new distributor, but there was never a water pressure problem. it has sat on the trailer since being at the dealer, so I doubt it is related to the impeller, however the thermostat could have gone bad over the winter.

I looked at some FAQ's and they say that as long as the temp stays in one spot it should be alright, and it does stabilize around 210.

also, just found out that the gasket in the water strainer was not installed. been told this could cause the problem. only problem is I have to put it in the lake to test the strainer...

thanks!!!

[Rick]

If you don't have the gasket then you are probably pulling alot of air with the water. This could definately cause you to run hot. However if everything feels cold I would suspect either a bad ground or bad sensor. Try this, detach the lead from the temp sensor, start the boat. short the wire to the engine block then touch it to the sensor. If you get the same reading with both touches replace the sensor.

[MiracleDriver]

that's great advice, thank you.... is the temp sensor the one right by the waterpump and coil on the top of the block?

[MiracleDriver]

okay...

got the gasket in, but there is still a problem.

tried touching the lead to the block and the sensor, but you only get a reading from the sensor so it seems to be working.

initially when I had installed the strainer again the boat got hot.

I stopped it and loosened all of the hoses to look at the impeller. it looks perfect from the above angle and it is definitely getting water.

when I did everything up again, the temp seemed to be lower. from 170-180, but it acts weird.

from 10-20mph the temp sits right around 170. when you give it gas it rises and when you give it WOT it gets right up to 210 or so.

when you back it off, it seems to run cool, especially around 10-15 mph when the nose is in the air...

I'm lost.. please help!!!!

[coloradonautique]

Miracle,
You definitely need to figure out whether it is the sensor, the gauge or a water supply problem. I am leaning towards the first two since you say the risers and engine are cool to the touch. I sold my '90 but here are a couple of things I remember.

You actually have two pumps on that engine. A sherwood supply pump (belt driven on stbd front side of engine) and a circulating pump (hidden behind main pulley?). A good water supply test is to run a short hose from the intake/strainer into a 5 gal bucket on the ground while the boat is on the trailer. Then fill the bucket with a garden hose and start the engine. This does a great job of simulating the lake. It actually is the worst case scenario since the supply pump has to pull water from 5 ft below the engine without any help from water displacement or garden hose pressure. Let the engine get to temp and you should start to see water come out of the exhaust. If you rev the engine, you should literally shoot water 5-8ft out the exhaust. Check how quickly it pulls water from the 5 gal bucket. Without the garden hose running, it should empty the bucket in 15 seconds at 2000rpm. Faster at high rpms, slower at idle. Make sure you are seeing this trend otherwise something is leaking air or the pumps are not working right.

If you have a voltmeter handy and some resistors from radio shack, you can diagnose the sensor and gauge. I cannot remember whether the temp sensor is a one wire or two wire setup. I am thinking one wire which means it is grounded through the block and easy to work with. Let me know which it is and I will post some additional things to try.

If you short the wire to the engine block, I think you should have got max temp on the gauge. Most auto temp sensors are high resistance = cold ; low resistance = hot.

Regards,

Lorin

[coloradonautique]

Based on your last post about the good temp at idle, bad at higher rpms, you could potentially have a bad thermostat that is only partially opening. It is fine at idle when a little water flow can keep up with the engines heat output, but once you start pushing rpms and creating more heat, the partial opening cannot let enough water through to keep up. It's a $12.50 thermostat and easy install so it might be worth trying. Skidim or whitelake will have them in stock.

http://www.shopwhitelake.com/thpcmfoen160.html

[MiracleDriver]

checked the sensor. it doesn't read anything when you touch it to the block and it reads when you touch it to the sensor.

I just ran it at the dock... when at idle it gets hot and the temp light comes on. when you give it some gas it drops back down to 170.

like I said before when out on the water it goes up to 200+ when running over 35mph. runs at 170 and no temp light when between 10-20mph.

the RWP and risers are cold to touch when running. as are the hoses to the risers. the hose that runs down from there to the circulating pump is hot.

also, when you shut off the motor the hot water runs back through everything and the pump and risers are hot. not sure if this is a problem.

thanks for your help so far guys, keep it coming.

MD

[MiracleDriver]

so I tried to test to gauge now.

I used skiDIM's faq: http://skidim.com/Faq_TROUBLESHOOT.asp#RWTS

took the wire off (there are 2 and 1 ground) and attempted to ground each of them to the block. I didn't get any reading on the gauge from either wire,

except when I disconnected the ground wire the gauge is pegged. it will peg no matter if it is grounded or not.

could my gauge actually be bad?

[coloradonautique]

Miracle,
That is definitely leading me towards a faulty thermostat.

My thoughts are: When thermostat is closed, RWP pushes water through the bypass to the risers. Hence cold RWP pipes and risers. The circulating pump is re-circulating water through the engine until it reaches optimal temp (170) and then the thermostat opens and closes to let cold water into the circulating path from the lake to maintain the 170 optimal temp. Definitely replace the thermostat.. If that doesn't do it, I would look at the circulating pump although it is rare for those to fail especially if the engine has never seen salt. I've only seen one circ pump ever fail and it was on my Chevy pickup with 200K+ miles.

Here is the pump link.

http://www.skidim.com/prodinfo.asp?number=WP-2225MNRH

[coloradonautique]

Your results from the gauge testing makes some sense. I think.

I would expect the three wires on the back of the sensor to be:

Ground
Sensor Input
+12V supply

You need both Ground and +12v connected for the gauge to work at all. Then if you touch the sensor lead to Ground the gauge should peg. If you touch the sensor lead to ground with say a 10,000 ohm resistor, you should get some reading but not pegged.

I actually would have expected four wires on the back. With one lead being the backlight... although that could be a seperate bulb inserted into the case.

Given your results of varying temps at different running speeds, I am skeptical that it will turn out to be the gauge.

As Skidim suggests. Try removing your T-stat and see if the engine runs cold all the time. You may also find you just have a piece of impeller or something blocking/screwing with the T-stat operation.

T-stat is real easy to get at. Dead center on top of the front of the engine. 2 Allen bolts (I think) and you are there.

[MiracleDriver]

Based on your last post about the good temp at idle, bad at higher rpms, you could potentially have a bad thermostat that is only partially opening. It is fine at idle when a little water flow can keep up with the engines heat output, but once you start pushing rpms and creating more heat, the partial opening cannot let enough water through to keep up. It's a $12.50 thermostat and easy install so it might be worth trying. Skidim or whitelake will have them in stock.

http://www.shopwhitelake.com/thpcmfoen160.html

is that the thermostat to use? it says 94 and up efi. I have a 1990 carb 351.

I tried to loosen the 2 allen bolts on top of the thermostat and they will not budge... what kind of torque should they be tightened to? because I can't undo it with my hands...

checked the impeller and its mint.



how quickly do boats burn? lol :twisted:

[coloradonautique]

Yup.. If you have never had it off it will probably be tough. I always use an allen socket and a long handled socket wrench with an extension. You should be able to get it. No idea what the torque specs are but I cannot imagine it is much.

I thought all the ford 351s T-stats were the same (other than temp range) but I could be wrong. Ask Skidim or whitelake, just in case.