2000 Volvo 7.4L GSi PEFS s/n-4012007357, approx 300hrs--w/captain's call exhaust. Volvo DP-SM drive s/n-4112093422
I have a very specific overheat problem that not even the mechanics can figure out. So here it is..... We bought the boat used and have had it for three years. We boat at the Lake of the Ozarks and as far as I know, the boat has never been in salt water. Last year I went ahead and replaced the impeller...no problems, just for preventative maintenance. The old impeller looked good...no pieces missing, just looked used. After getting it back together and out on the water, I noticed that at around 3100-3200 rpm the temp would start to rise quite quickly and I soon got the overheat alarm, I pulled it back and the temp would start to go back down. So I went ahead and changed the thermostat as well. When I opened up the housing, there were no problems, no chunks of anything; nothing stuck in the thermostat. Went ahead and put a new one in and even tested the old one using a pot of boiling water and infrared heat gun to check the temp and it opened up right when it should have. Re-installed the thermostat with new ring and gasket and took off the raw-water pump housing to re-check the direction of the impeller vanes. The impeller was installed correctly and looked fine. Still overheated around 3200 rpm. Checked all the hoses and water flow (on and off the muffs) and everything looked good. Used the infrared heat gun to check the block and t-stat housing (to make sure it wasn't a gauge or sender issue). Gauge and sender seemed to be operating fine as the gun showed the same temp and subsequent overheat. Runs great and solid.....no stuttering or stumbling.
I also changed the exhaust bellow around the same time; I just don't remember exactly when. When I bought the boat, it had a straight exhaust hose that was clamped on the stern side via a hose clamp. The other end (where it contacted the drive) was not attached. When the drive was down, it simply slid into that end of the bellow, allowing the exhaust to exit throught the drive. Once you raised the drive so far, it would lose contact with the hose. I asked the parts guy about this who looked it up and said that it should have the accordian style bellow that hose clamped on both ends. So I bought the accordian style bellow (which was not cheap) and put it on. I was later told that either bellow could be used.
Take it to the shop this year and tell them exactly the issues I was having and what I had already done. They took detailed notes and asked detailed questions. They suggested that perhaps the intake hose on the outdrive was collapsing under the pressure or maybe even a wrong impeller was installed. They doubled check my part #'s and confirmed I had purchased the correct parts (they were purchased from their parts counter). Anyway, they keep the boat and call me a couple of weeks later and tell me that I had done everything correctly and were following in my footsteps and could not find any problems with what I had done. They said they went ahead and put in another new impeller and t-stat and put on a new water pump housing (all brass) as the old one looked a little worn and was partially plastic. When they water test it, they take it up to about 4000 rpm, going about 50 mph for over a mile and saw no problems and had no overheat. They said it ran real strong, sounded great with no overheat and thought they may have solved the problem (with a new housing). However, they said that when they brought it back to around 3200 rpm, the temp started to rise and act just as I had described. Once they pulled it back even further, the temp would start to drop quickly and cool down again. Does the same thing with or without silent choice exhaust.
They bring it back, run more tests......check to see if the computer had thrown any codes-negative results; checked compression of the cylinders and everything checked out within normal range. They call Volvo and talk with them for about an hour and they are stumped as well. I asked if they thought there could be debris somewhere (manifold, oil cooler etc.) and they thought it was unlikely due to the fact that it only seems to overheat at that one specific rpm range. They put the clear hoses on and water test again to see if it was sucking air and found no problems; just the slightest miniscule stream of small bubble at all ranges. They checked the timing at the different rpms and found no problems.
They said they have ruled out any collapsing hoses as it doesn't overheat above and below 3200 rpm and gets good water flow at any rpm. They said they looked at cavitation issues around the drive and found nothing. They also said they did not believe it was a cracked block or head gasket issue but without tearing down the engine they couldn't rule it out 100%. The engine has never used a lot of oil and it always looks good when I check the level and when I change it.
So.....anyone have any suggestion?????? Sorry for the lengthly post but I think it is easier to make an informed opinion/decision/suggestion with all the facts at hand. I know I probably have left something out that may have been done, so don't hesitate to ask any questions.
Thanks,
Jeff
I have a very specific overheat problem that not even the mechanics can figure out. So here it is..... We bought the boat used and have had it for three years. We boat at the Lake of the Ozarks and as far as I know, the boat has never been in salt water. Last year I went ahead and replaced the impeller...no problems, just for preventative maintenance. The old impeller looked good...no pieces missing, just looked used. After getting it back together and out on the water, I noticed that at around 3100-3200 rpm the temp would start to rise quite quickly and I soon got the overheat alarm, I pulled it back and the temp would start to go back down. So I went ahead and changed the thermostat as well. When I opened up the housing, there were no problems, no chunks of anything; nothing stuck in the thermostat. Went ahead and put a new one in and even tested the old one using a pot of boiling water and infrared heat gun to check the temp and it opened up right when it should have. Re-installed the thermostat with new ring and gasket and took off the raw-water pump housing to re-check the direction of the impeller vanes. The impeller was installed correctly and looked fine. Still overheated around 3200 rpm. Checked all the hoses and water flow (on and off the muffs) and everything looked good. Used the infrared heat gun to check the block and t-stat housing (to make sure it wasn't a gauge or sender issue). Gauge and sender seemed to be operating fine as the gun showed the same temp and subsequent overheat. Runs great and solid.....no stuttering or stumbling.
I also changed the exhaust bellow around the same time; I just don't remember exactly when. When I bought the boat, it had a straight exhaust hose that was clamped on the stern side via a hose clamp. The other end (where it contacted the drive) was not attached. When the drive was down, it simply slid into that end of the bellow, allowing the exhaust to exit throught the drive. Once you raised the drive so far, it would lose contact with the hose. I asked the parts guy about this who looked it up and said that it should have the accordian style bellow that hose clamped on both ends. So I bought the accordian style bellow (which was not cheap) and put it on. I was later told that either bellow could be used.
Take it to the shop this year and tell them exactly the issues I was having and what I had already done. They took detailed notes and asked detailed questions. They suggested that perhaps the intake hose on the outdrive was collapsing under the pressure or maybe even a wrong impeller was installed. They doubled check my part #'s and confirmed I had purchased the correct parts (they were purchased from their parts counter). Anyway, they keep the boat and call me a couple of weeks later and tell me that I had done everything correctly and were following in my footsteps and could not find any problems with what I had done. They said they went ahead and put in another new impeller and t-stat and put on a new water pump housing (all brass) as the old one looked a little worn and was partially plastic. When they water test it, they take it up to about 4000 rpm, going about 50 mph for over a mile and saw no problems and had no overheat. They said it ran real strong, sounded great with no overheat and thought they may have solved the problem (with a new housing). However, they said that when they brought it back to around 3200 rpm, the temp started to rise and act just as I had described. Once they pulled it back even further, the temp would start to drop quickly and cool down again. Does the same thing with or without silent choice exhaust.
They bring it back, run more tests......check to see if the computer had thrown any codes-negative results; checked compression of the cylinders and everything checked out within normal range. They call Volvo and talk with them for about an hour and they are stumped as well. I asked if they thought there could be debris somewhere (manifold, oil cooler etc.) and they thought it was unlikely due to the fact that it only seems to overheat at that one specific rpm range. They put the clear hoses on and water test again to see if it was sucking air and found no problems; just the slightest miniscule stream of small bubble at all ranges. They checked the timing at the different rpms and found no problems.
They said they have ruled out any collapsing hoses as it doesn't overheat above and below 3200 rpm and gets good water flow at any rpm. They said they looked at cavitation issues around the drive and found nothing. They also said they did not believe it was a cracked block or head gasket issue but without tearing down the engine they couldn't rule it out 100%. The engine has never used a lot of oil and it always looks good when I check the level and when I change it.
So.....anyone have any suggestion?????? Sorry for the lengthly post but I think it is easier to make an informed opinion/decision/suggestion with all the facts at hand. I know I probably have left something out that may have been done, so don't hesitate to ask any questions.
Thanks,
Jeff
