Hello
New to the forum, hoping to find someone with some knowledge to help me fix an issue i am having with my boats motor. Apologies for the long post, but for those who like a problem, i am sure you will enjoy!
Details as follows: INDMAR LT1 V8 Corvette motor - 1997 make, 500 running hours. Inboard ski boat, Mid mount.
SYMPTOMS:
- Once the engine has been operating for at least 20 minutes, when brought up to cruising speed from a standing start (such as pulling up a skier) when the engine is under load, the engine temp rises rapidly from 150F (normal operating temp) to ~200F when the management takes over and shuts down the motor.
- The temp can be brought back to normal (equally as rapidly - nearly instantaneously! which i know is not good for anything) by a quick "blip" of the throttle, which appears to restart the cooling.
- The problem does not happen at any speed if the engine is not put under excessive load, ie, i can run it at WOT with no problem so long as i take it there slowly.
WHAT IT IS NOT! I have been over the cooling system and checked / replaced the following parts, none of these have fixed the problem.
- Raw water impeller, replaced (was due anyway), not the problem, good water flow
- Raw water thermostat, replaced also ran without, not the problem
- Cooling circuit, does not appear to have any blockages
- Engine side thermostat, replaced, not the problem, Ran without, NOT OVERHEATING but runs too cold, as expected (~110F), and the EFI management stays in cold start calibration
- Water pump, replaced, was squeaking, thought it could be sucking air through the bearing (cam driven not belt), did not fix the problem although the engine doesn't squeak anymore! (have to take the good with the bad!)
WHAT I THINK THE PROBLEM MAY BE I think i may have done a head gasket. But i am open to other suggestions from anyone who may have a bit more knowledge on the engines. I figure water is pouring into the exhaust (or exhaust into the water) when the engine is under load, creating a hot air pocket under the engine side thermostat which is preventing it from opening and causing the problem. Potentially it is only when under load that this seal is "blowing out", which is why i can run all day so long as i take her to speed slowly. There are no other leaks, could the cooling circuit be sucking air from anywhere else?
CAN YOU HELP?? (PLEASE!) Before heading down the track of tearing the engine apart, i am hoping that i could get some comment on my "diagnosis" and any other potential problems i may have missed. Also keen for some advice on the following:
- Is there any way to confirm this (given that it is an intermittent) prior to pulling the engine apart? Especially with relation to which cylinder bank has the problem.
- Although i do know the common sense answer to this question, am i likely to do the engine any harm running without a thermostat (other than running a bit rich on cool start calibration) to keep the engine cool and not putting it under load. For various reasons, ideally i need to get a few hours out of the engine before i can get this maintenance done.
Apologies agian for the long post. This problem has stumped at least half a dozen marine mechs over here (Australia) and i am keen for resolution.
Cheers Michael S
New to the forum, hoping to find someone with some knowledge to help me fix an issue i am having with my boats motor. Apologies for the long post, but for those who like a problem, i am sure you will enjoy!
Details as follows: INDMAR LT1 V8 Corvette motor - 1997 make, 500 running hours. Inboard ski boat, Mid mount.
SYMPTOMS:
- Once the engine has been operating for at least 20 minutes, when brought up to cruising speed from a standing start (such as pulling up a skier) when the engine is under load, the engine temp rises rapidly from 150F (normal operating temp) to ~200F when the management takes over and shuts down the motor.
- The temp can be brought back to normal (equally as rapidly - nearly instantaneously! which i know is not good for anything) by a quick "blip" of the throttle, which appears to restart the cooling.
- The problem does not happen at any speed if the engine is not put under excessive load, ie, i can run it at WOT with no problem so long as i take it there slowly.
WHAT IT IS NOT! I have been over the cooling system and checked / replaced the following parts, none of these have fixed the problem.
- Raw water impeller, replaced (was due anyway), not the problem, good water flow
- Raw water thermostat, replaced also ran without, not the problem
- Cooling circuit, does not appear to have any blockages
- Engine side thermostat, replaced, not the problem, Ran without, NOT OVERHEATING but runs too cold, as expected (~110F), and the EFI management stays in cold start calibration
- Water pump, replaced, was squeaking, thought it could be sucking air through the bearing (cam driven not belt), did not fix the problem although the engine doesn't squeak anymore! (have to take the good with the bad!)
WHAT I THINK THE PROBLEM MAY BE I think i may have done a head gasket. But i am open to other suggestions from anyone who may have a bit more knowledge on the engines. I figure water is pouring into the exhaust (or exhaust into the water) when the engine is under load, creating a hot air pocket under the engine side thermostat which is preventing it from opening and causing the problem. Potentially it is only when under load that this seal is "blowing out", which is why i can run all day so long as i take her to speed slowly. There are no other leaks, could the cooling circuit be sucking air from anywhere else?
CAN YOU HELP?? (PLEASE!) Before heading down the track of tearing the engine apart, i am hoping that i could get some comment on my "diagnosis" and any other potential problems i may have missed. Also keen for some advice on the following:
- Is there any way to confirm this (given that it is an intermittent) prior to pulling the engine apart? Especially with relation to which cylinder bank has the problem.
- Although i do know the common sense answer to this question, am i likely to do the engine any harm running without a thermostat (other than running a bit rich on cool start calibration) to keep the engine cool and not putting it under load. For various reasons, ideally i need to get a few hours out of the engine before i can get this maintenance done.
Apologies agian for the long post. This problem has stumped at least half a dozen marine mechs over here (Australia) and i am keen for resolution.
Cheers Michael S
