White steam / smoke

the riser gasket blocks off the front passage not the rear passage or the two side passages. If it is blocking the rear passage then all of the water almost instantly goes out the riser and does not circulate in the manifolds. Call Vince and double check me but I'm almost 99% sure that's the way it should be.

79,

That is what I thought also. When Marks said that, I checked Skidim's website. It says:

"GSKT EXHAUST RISER
PCM FORD AND PCM GM SMALL BLOCKS
The blocked water passage goes towards the exhaust outlet. Same Gasket 3" and 3.5" Risers."

I'll call Vince in the morning to make sure. Had to order 2 new ones from them tonight anyway. Took the risers off tonight, but no way to save the gasgets.

Put the new riser gaskets on with the exhaust outlet side (back) blocked. It was better. Still got some steam / smoke at full throttle, but not much. Did not have any when accelerating. Definitely better.

Came back down the canal (couple minutes at idle). Risers were not as hot as before, but still hot. Could hold hand on there for a few seconds, maybe 10, but not indefinitely.

My raw water pump test results from a few days ago were:
With boat in the water, hose from top of raw water pump filled a 5 gallon bucket at 2500 rpm in 21 seconds.
Hose going into driver's side manifold filled just under half of the 5 gallong bucket in 20 seconds.

Manifolds and risers are new.

Any thoughts.

Went out today and checked temp of risers. I can't leave my hand on them for 5 seconds. Did some of the above prescribed work today.
1. checked water pump flow. ok
2. chased all hoses from water pump through thermostat to manifolds. ok

I've never burned up an impeller since I've owned the boat. Now I'm wondering if the PO did and there are pieces in the manifold or something. What do you suggest next? I guess checking to see if the riser gasket is turned the wrong way, but I'm nearly certain it's turned so the blocked portion is toward the stern...I remember following skidim instructions when I changed them.

This is starting to bug me and I didn't even know it's a problem. I did notice that there was steam coming through many, many boats' exhaust tonight though. Does humidity matter? We have steam coming off our grass most summer mornings here...
Either way, according to you guys, my risers are way too hot.

Azeus17,

I don't think I ever solved anything on mine. I still have a steam issue. I don't think mine is just weather or climate related, as it does it when it is hot or cold, wet or dry outside. We pulled the boat to Lake Lanier in GA this summer and it even did it there.

While the steam is there most of the time at acceleration, I don't seem to have any other problems. Boat runs pretty good and temp gauge stays from 150 - 165. We are just using it as is.

Over the winter, I may swap out the raw water pump and hoses from the intake to the pump.

Have you run the raw water pump test? That can show you a lot.

Another thought, and I know the weather conditions have been discussed, but the water temp where I am running is nearly 90. At that temp, can I still expect the engine temp to stay right near 160? I even put a 140 tstat in, but the temp still hovers just north of 160 when at idle and lower RPM's and goes up to about 190-200 after a high speed run and then drops back down.

Boat doc

I think I disagree with you on this one some days I get steam along with my water coming out of the exhaust. I know I have no cooling issues as I can hang on to the manifolds at idle and WOT all day long.

Now I agree with you that if he can not hold onto his manifolds and risers he has a problem. But once he can hold on to them and he gets a some steam from the exhaust outlets then he is ok.

Boat doc,

I started another thread about an overheating problem I am having, but have been watching this thread too. I have overheated twice in the past month, first time temp gauge went up, second time it didnt. Ran boat several hours between the two incidents and it was fine. I noted what you said about leaking RWP. I replaced my impellor this spring(Chev 305 w/OMC conv - big impellor-big fins)
I had to fashion my own new gasket. It drips ever so slightly with garden hose hook up. Drip goes away when engine is running. Since the overheating just started this year (after the pump servicing) could that ever so slight a leak be indicative of enough air getting in to cause a problem. Note: I ran over 20 hours this year before the problem showed up. If you have a moment, look at my "overheating" thread that has some more detail. I'd appreciate your input.

Thanks,

Larry

75, if it leaks under pressure...it'll leak under vaccuum(sp?)

This is incorrect ,an impeller type pump would rather suck air than water, and a small air leak at the seal will cause a substantial loss in cooling flow,causing an overheating situation.
The same pump will most likely exhibit no external leaks nor any visible symptoms as to the integrity of the seal.....boat dr

The block and the risers are cooled by the same water,both should be the same temp. Have seen cases or "insulation" from silt & sediment collecting at the rear of the block restricting or stopping water flow around the cyls.
Would not be hard to check, remove a "FREEZE PLUG" on each bank at the rear and look. I know this sounds like a long shot, but stranger things have happened....boat dr

FREEZE PLUG? is that a hidden message?

Well, took her out again today and I have mixed emotions. On one hand the temp gauge read 160-180 the whole time. On the other hand the block and oil pan and valve covers were hot as hell. Not sure exactly the temp ( I have the IR thermometer OTW, bought on line). I am still getting some white smoke out the exhaust. Here is what I have done so far:

tstat
Impeller
temp sending unit
RWP test-fine
Circ pump test-fine
cleaned strainer

I have all new hoses on the way from DIM and tomorrow I am going to take the tstat out all together and see what happens.

I am still thinking that there is a clog somewhere in the cooling lines in the block. I don't know enough about the route they take though. Anyone have an idea where they might bottle neck and allow a build up?
I have an idea to unclog whatever might be there. Can anyone tell me if I can do this without harming the motor. If it screw a fitting into the block drain and attach the hose to it and take the inlet hose off the circ pump and try to reverse the water flow. Has anyone tried it or know if it would harm in any way. i.e.- water in the cylindars???

Maybe everything is fine. Vince at DIM seemed to think that if I have good flow everywhere, it should be fine. All I read on this site, though, is that engine should be cool enough to lay your hand anywhere.

HELP!!!!

Azeus17,

"All I read on this site, though, is that engine should be cool enough to lay your hand anywhere."

This statement is not completely correct. Since you have a 140 degree thermostat, this means the water in the block will be regulated to a temperature of around 140 degrees. To put this in perspective, most home hot water heaters are set for 130 degrees. 140 degrees is considered scalding hot. This doesn't necessarily mean that the entire engine will be 140 degrees. The bottom of the exhaust manifolds, where they attach to the heads, does not have a water jacket. This area gets very hot. Also, since these engines do not have oil cooling systems, the oil temperature may be 10 to 20 degrees higher than the water temperature, meaning the oil pan may be hotter than 140.

The exhaust risers are not subject to the thermostat. All excess water from the raw water pump is dumped into them along with the output water from the block. As others have said, the exhaust risers should be cool enough to touch all day long. If they are running too hot to touch, it is usually a sign that the raw water pump is not keeping up.

One other note. 160 degree thermostats are common in the PCM 351. Are you sure yours is 140? You may have ordered a 140 degree but received a 160 degree. You might want to consider testing it.

Hope this helps,
Mark

Tim,

I get some steam too in my 89. Some days more than others. Temperature and humidity must come into play. We are mixing water with very hot exhaust gas.