99 Mastercraft w/ corvette motor cooling issue, need help
 

I have a buddy with a 99 Mastercraft 230VRO with a corvette engine. The motor has two tstats. Engine runs 165 ish all the time the last several years.

the issue: late last year temp started to run at 200-210f.

end of season came, replaced impeller, which was fine, also replaced a 145 and 160 f tstat. Engine still ran 200-210.

this past week, new engine circulation pump was installed. Same thing.

The engine then had a mechanical gauge installed…. It read the 200 as well.

pulled the 160 tstat, (main one in traditional engine location) the water temp runs 150.

has anyone every worked on an engine like this and do you know what went astray to cause the engine temps to rise from 165 to 200?

thanks for your help,
chris

Check for blockages in the incoming water. Is there a sea strainer?

We actually did check and flush. Disconnected water line from tranny heat exchanger and inspected and flushed. All was clear. No strainer, but inlet is wide open.

Also noted is the water physically leaving the bait via the exhaust looks normal, ie it looks like it’s moving the water through.

Closed cooling? LT1 (typed LS1 by mistake). From what I've read, the two thermostat system can trap air. I would go about trying to burp the system.

If it is open cooling system, try draining the block. You could have sediment or sand. It is amazing how much crap comes out of my blocks when I drain them.

As I read through the posts, this is what came back to me. I had a customer with a Centurion towboat where they had to pull the plugs (on trailer) and run the engine just to get the block to clear the silt (mid summer low water going into / from dock) then vacuum the bilge out. It would pack enough that a tech ignored the owner's instruction and didn't clear the block prior to winterizing, and the job was incomplete.....

Was the timing checked/ changed?

It’s an open cooling system, yes I believe the lt1 engine, indmar engine.

Did not flush engine, but did not see any silt or anything around tstat like had seen on other boats I’ve seen.

timing was never touched as the boat runs great, no issue power wise.

Does the marine version of the LT1 use the same optispark as the automotive version? If so, no provision for adjustment of timing.

I’m not sure of the differences.

I would still try to flush it next. Even let it idle for a few on the hose with the block drains out.