Ford 351 with PCM manifold heating up while idling

Hi all,
Well I can't wait to show you my 6 year restoration project on my 77' ski nautique. Will post pics in week or 2.

Before I get to problem - The long block, intake and all engine components are brand new. the boat was just started for the first time last weekend. I put a FWC system on it. New hoses - everything.

(I bought these 96' PCM manifolds and risers used - looked good from surface)

I am using a proflo system to flush boat on trailer. Plenty of water is flowing out the flappers equally on both sides. Raw water pump is new with new impeller.

The motor starts up fine. The motor idles fine. The intake, heads, valves and riser elbows are is cool to touch. The heat exchange is cool and warm right at thermo - like it should be.

After about 3-5 minutes I notice steam coming from the driver's side manifold. Really hot to the touch along the bottom especially- although the elbow and riser is not hot. The other side is cool.

Both heads are warm to touch and feel to be the same temp. Nothing alarming there.

I need some help. I don't want to jeapordize the new motor.

I read a few things on various forums. here are some of those:

- gasket on riser could be facing wrong way - no, mine has tab to rear.
- maybe my engine doesn't reach operating temperature when in idle.
It could be that when your thermostat is closed only 1 side of the exhaust get enough water (the cold side) and the other side get less - lots of water pouring out back on both sides so thinking something else.
- a guy mentioned that could be just hot at idle and higher revs will provide more flow pressure and work just fine - I am not comfortable with that.
- There is also a flapper on the inside of some of the exhaust manifolds that can stick in the closed position and cause this problem - I am thinking this may be the cause.

How do I know if manifold is bad?
Can I run some test on the manifold somehow somehow?

Problem 2:
Not sure about my temp sending unit (new too) / temp gauge - .
When I turn the key from a cold start the temp meter reads 190-200. As it idles the temp creeps up to 240 however the motor, block, intake, heat exchanger, valves and heads are barley warm not even hot -

So Im think something is up with temp unit or gauge. I am not sure how a cold motor can read 200 at start up.

Anyone got any suggestions for me? I sure could use some.

Thank you very much,

Mark

Mark,
Welcome to CCfan. With all the skilled tech help here, I know we can help. Heat exchanger? Do you have a fresh water cooling system?

When you got the new temp sender, did you match the Ohm range to the old gauge? Post some pictures showing the routing of the cooling system (hoses).

Make sure you get the pictures posted!!!

what is the condition of your RWP, it could be pulling air thru the seal or weep hole. airiated water completely looses its ability to transfer heat

Mark,
I'm glad to hear you're making some head way, getting answers and things are looking normal. I wouldn't worry about the steam out the tail end. Depending on the dew point you will get it. Since the starboard side is running hotter, it most likely got to the point where you got steam.

BTW, regarding the temp sender problem, don't shop at Autozone!!

water does take its easier path and yes at times will favor one side more than the other, how hot is hot? if you dont have access to a digital thermometer, simply put a heat thermometer on there and get some temp readings, they are exhaust manifolds and will get hot. one good way to gauge if you think they are getting excessively hot is to put some water on the hot manifold and if it instantly boils then you know its past 212 degrees.

What is the highest "safe" temp you can run at? I noticed my temps creeping up close to 190 at the end of the season. I am getting ready to put in a new circulation pump though. Came yesterday in the mail. Good shape and the internals look brand new. Hope that cools her down a few degrees.

Keegan and Dave,
You really do not want to get the engine close to boiling unless you have a FWC system. If it boils, the steam/air pockets don't tranfer the heat. On a FWC closed system like a car, the pressurization keeps the boiling from happening and the reason they can run pretty hot.

Keeganino wrote: I hope the new circulation pump brings the temp down.

Not that a circ pump failure couldnt cause you to overheat, but that sure doesnt seem to be a common cause on these engines.

Were you running hot at idle or at speed?

If at idle, you likely had an air leak- most likely a loose hose clamp. Its best to tighten them with a socket rather than a screwdriver.

If at speed, then you either have a blockage in a line, a failing impeller, or a RWP needing a rebuild.

Good troubleshooting tips Tim thanks.

I think it would run hot after a WOT run and seemed to stay hot longer than usual. That was a few months ago now so I dont remember exactly what was going on. My RWP is 3 years old and seems to be in great shape. I pulled the impeller when I winterized and it looks good but I will replace it anyway.

Could be a leak in the hose from the trans oil cooler since that is the only one I have not replaced. Blockage is certainly a possibility. I guess if its still running hot I will replace the hose and do a good poking around to look for blockage.

just opened cap to FWC and started motor.
for a brief second the temp did start out about 160, but climbed to over 240 within 2 minutes.

Going to check ground on gauge.

I know I need to check the temp gauge reading against actual temp of motor.
any suggestions how to do that ?
And where should i test ? (take sending unit out after heat up and test water under intake ???)

fellas ?

Will teflon kill your oil pressure sender too. Have not been able to get that to work and know it is teflon taped too.

Ok, cleaned the threads on both unit and intake.
Restarted with cap on and off of FWC and still
Same Problem

could my gauge not be grounded good.

Will be at all day tomorrow. got to get some work done today.

Need some suggestions.

Keeganino wrote: I think it would run hot after a WOT run and seemed to stay hot longer than usual.

Is it safe to presume that you returned the boat to idle after running at WOT? This is probably the most stringent test for the cooling system (very hard operation followed by minimal cooling ability at low RPM) so any weaknesses will reveal themselves. If getting back up on plane brought the temp back down, then you would likely have a minor air leak somewhere.

ok,
Then maybe the original hot wire is compromised somewhere between gauge and unit ??

ZenZeus wrote: ok, Then maybe the original hot wire is compromised somewhere between gauge and unit ??

No. If "comprimised", you ether wouldn't get any reading on the gauge (you do) or if the wire/connections/terminals corroded causing high resistance, then the gauge would read low.