Volvo 5.0 GL overheating at idle. Replaced thermostat and impeller. Cracked head?

[bhahs]

I have a 2004 Volvo Penta 5.0 GL with SX outdrive. I am overheating to 200 degrees at idle up to about 1500 RPM's. At 2000 RPM's, she's 160-165. I thought maybe the sender was bad so I bought an infrared temp gauge. Everything is reading 165 or less except the block and heads. The risers and manifolds are cool. I've taken off hoses while running and I have good flow. I have replaced the thermostat and impeller with factory Volvo parts. I have removed all hoses with no blockage. I took off the risers and they look new inside. I took off the circulating pump and it looks great. There is plenty of water coming out where the lower unit bolts to the transom. The lower unit has 2 holes on each side about midway down that have water streaming out of them. I have not taken off the lower unit. Some people are talking about seals that are bad which can cause air leaks. I guess that's a possibility? I'm wondering if I have a cracked head or bad head gasket which is allowing exhaust to get in the water flow causing it to heat up at idle. Is there a way to pressure test the heads without removing them? I'm not sure what else to try?

 

[bhahs]

I wanted to add that there is no water in the oil that I can see. She starts and runs great. Even when hot, she starts fine. No steam out the exhaust that I can see. The temperature alarm has never gone off. Runs perfect!

 

[John2037]

It does sound like an air leak. Get some clear hose and a union to put in line at the water inlet on the tstat housing to inspect. If you see bubbles then put it on the inlet of the water pump - no bubbles then you've got pump problems, bubbles still then you've got to trace it further back.

 

[mikeneal]

On my SX I once had the plastic fitting where the water inlet hose goes thru the transom under the gimbal bell and it caused odd over heating issues . Was cheap enough and easy fix, might be worth looking at, (cracked on backside so actually couldn't see it easily until it was removed.

 

[bhahs]

Put the clear hoses on today and absolutely no bubbles. Looking more like cracked head. It's just weird that the boat runs so perfectly. Not so much as a miss at idle or any rpm.

 

[bruceb58]

Are you running on muffs or in the water?

I don't think a cracked head is going to cause an overheat condition on a boat with raw water cooling.

Sounds to me like you have a cooling water flow issue.

 

[Sparkinator]

I had an overheating issue at idle/low rpms. I tensioned the raw water pump belt and the problem went away.

 

[bhahs]

It overheats in the water and on muffs. I made sure the belt was tight. As a precaution, I bought a new belt and still didn't help.

 

[gbeltran]

Did you check the passages in the thermostat housing? How about a little history, total hours, salt or fresh water, did this start this year when you fired up the boat for the first time, you just got it, it's been an ongoing thing....etc. When you say you took off the recirc pump did you remove the back cover and inspect? Just to be clear when you say recirc pump your talking about a cast iron piece that bolts to the front of the engine and not the pump with the rubber impeller? Don't be offended, have to ask.

 

[tkrfxr]

Also, please check, and make air-tight, if you have them, #1 the cap on the engine flush hose and #2 the connections on the NeutraSalt flush system.

#2 was a source of low RPM overheat alarm in my boat some 6 years ago....I had left a hose connector open at winterizing, and forgot to re-connect. In the spring, the boat went in the water, out for a spin and alarmed when at idle at returning to the dock....drove me crazy! Once re-connected properly, no more alarm.

 

[bhahs]

I bought this boat this year. Ran fine first time out. Second time out is when idle overheating began along with stiff power steering. Found loose belt and figured this would fix the problem. Well, I fixed the power steering but not the overheating. No hour meter. Always in fresh water. Bought it from original owner. I did take the back off the circulation pump. The thermostat housing is clear. I did make sure the blue cap was tight. I'm not sure if I have a Neutra Salt System? Where would that be? My alarm has never gone off. Everything that I shoot with the lazer thermometer seems to be cool except the block.

 

[John2037]

IMO a cracked head will cause more problems than what you're seeing - water in the oil would be likely, and problems are usually the opposite, worse at higher rpm's... I wouldn't think you have a neutral salt system for a fresh water boat but it ties into the cooling system to inject neutrasalt solution into the engine to cut down on salt corrosion. As ~~mikeneal said, a very common problem is there's a water nipple on the outdrive intake hose that cracks and will suck air, but that normally causes problems when your on plane or muffs because it's under water when you're not + you would have air bubbles in the hose. Everything except for the block should be cool since water always flows - block is regulated by the t-stat. How did you check the recirc pump? They aren't much and from what you say you've tested, it does lean to that, a flow problem or a bad/wrong t-stat. Guess you could pull the t-stat and see how that runs.

a. How hot was the block on your ir gun?
b. A cylinder compression test would tell you if you have any gasket/mechanical problems.

 

[bhahs]

I've overnighted a new complete raw seawater pump. Even though mine shows no wear, I'm hoping from several suggestions, this is the right way to go. I read one person said they had .010 wear on just a corner and it overheated at idle. Not much room for error! $350 gamble.

 

[jfpound]

Do the compression check. Sounds just like how mine behaved with a bad head gasket.

 

[bhahs]

Just tested boat out with new complete water pump and still overheated! UGH!!! I will check compression next. Thx Jeff.