Engine overheating at high speed
 

Engines runs fine at low/mid range speeds but temps really climbs when I hit the throttles hard.

Thermostats had been drilled (1 hole) but that didn't help.
Took the guts out of the thermostats and that seems to have solved the problem but now I don't have decent engine temps.
Is there a high volume thermostat out there - or maybe another cure?

Engines are 502's with crossovers...

G-

What temps are you seeing at W/O ?? My boat runs at only around 120 degrees after a hard run when it is 80 degrees outside.

Are your sea pumps new/rebuilt ??? It sounds like you have enough flow if the temp drops when the t-stat is out. You might need to find a happy medium with a restrictor plate in place of the t-stat.

Have you checked the oil temp when the water temp is hot??? Your oil coolers might not be sufficient enough.

Also check your timing. If it has too much advance it will run hotter. I believe you want a max of around 34 degrees from 3000 rpm to redline. Timing too far advanced will also drive up oil temps.

Later Bro--

This is usually a result of the water pickup sucking air at high speeds. Is your boat so fast that it needs a low water pickup? Is there something on the boat bottom adding air to the water that is passing by your intake?
Sincerely
Dennis Moore

We backed off after 160+ degrees with no sign of the needle slowing down.
Everything on the engines are brand spanking new.

Now running 105 without T-stats.

Definitely thinking the T-stat is too restrictive - could go with an automotive one but really don't want to be changing them every year when the finally start sticking.

I'll have to see what oil temp I'm running - using straight 40 weight Schaffer (sp?) and have great pressure.

See ya! Matter of fact....I'm leaving the office in 20 minutes to go tool around and waste some gas on the boat. Today and tomorrow....in the 80's. After that....brrrrrrrrrr.:D

hey G, what temp thermostats do you have in there? Also is the oil cooler or if you have a powersteering cooler too small? maybe that restricting the water flow at higher speeds? How about the intake hoses? are they new as well? maybe they are colapsing on high rpm's due to vacume from the sea water pumps? :)

Do you have sea strainers? They may be filled.

Check your water hose too, pickup to the water pump. It could be collapsing internally.
Gary

Arizona Speed and Marine have the high flow T-stats. I bought some 120's. I think they have 140 as well.

Just another thought, my 502 would use oil to the tune of 1 qt per 5 hours on some trips. Other times I could go 5 and not use a drop under similar conditions. Once the 120 t-stat was installed oil consumption has gone to maybe 1/2 quart in 10 hours. I am running the 120 because of the blower. Oil consumption never really changed even with the addition of the blower.

I see the engines are new, but is the boat and drives old?

I have seen the water hose from the transom assembly to the bell housing collapse at high speed. I have also seen salt build up where the water hose attaches to the transom assembly reducing flow.

I had a problem similar to this. The motor had no thermostats, showed water pressure, but almost burned one CMI header down at top end. I tried everything I could think of. The start of the next season I had no water movement at all. The sea pump impeller was replaced, and the rubber tips of the old one were pitted. Problem went away!

You might look at the intake ends of your coolers there may be something obstructing the flow.

You could have someone observe your tailpipes at WOT to check the flow. I had one header running dry, but only at top end.

These are just some additional thoughts.

HERE`S THE ANSWER:
 

I had the SAME EXACT problem earlier this year. I tried t-stats among other things. No change.
Several people suggested my impeller was bad. I thought: no way, I just put a new one in this spring.
I pulled it anyway and found that the corners of each blade were damaged. I popped in a new impeller, no more overheating!!!!!!

I replace my impellers every 2 years as part of preventative maintenance. It's pretty easy once you get used to it. Its a real pain once they fall apart and you have to get all the pieces out.

The correct type of water hoses usually have a wire sandwiched in them to keep them from colapsing.

KAAMA
I've had 2 boats where the inner lining of the hose "delaminated". It would collapse to less than 1/2 normal size. The outside of the hose still felt solid because of the wire support in it. You could only tell by looking down the hose itself. The hoses were about 10 tears old though.
Gary