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Volvo Penta v8 running hot 200degrees

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Volvo Penta v8 running hot 200degrees

Old 06-10-2021, 12:47 PM
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Default Volvo Penta v8 running hot 200degrees

Posting for a friend- I have been helping him over past few weeks with a running hot issue. Below is what we did but still runs a steady 200 degrees.
1986 5.7 Volvo penta (new vortec long block 2 years ago) with volvo 290 outdrive. Closed cooling.
1- Replaced water pickup housing and gasket on top of outdrive.
2- Replaced all salt water hoses from outdrive to water pump. (belt driven sea water pump)
3- Replaced impeller.
4- Replaced thermostat.
5- Removed and inspected circulator pump. (came with new motor and was fine). I also verified water flow thru block from rt side to left side with garden hose.
6- Boiled heat exchanger.
7- Removed and inspected risers. Clear as a whistle. (Also new 2 years ago including manifolds.)
8-Replaced temp sensor, wire and guage. Old one would be pegged at 220 and jump around so this was definitely bad.
When underway the exhaust elbows are only warm. They never get hot. There's plenty of salt water flow. Antifreeze is topped off.
Before all this work was done, the gauge would jump to full 220degrees. We would place in neutral and give gas and it seemed to cool down to about 200 until we took off again. Even when engine seemed to be too hot, manifolds are only warm.
After all that work was done, it now runs steady at 200 degrees. Doesn't ever rise or lower. This engine should run about 160degrees. I don't want to think the unthinkable of a bad head gasket, but the engine runs and idles perfectly.
Did I miss anything? At this point I'm stumped and recommended him to bring to a local shop, but there all too busy right now.



Old 06-10-2021, 01:13 PM
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if bad head gasket
you'll either loose coolant in the closed system or you'll see bubbles in it or Both
how often does the coolant need topping off ?

did you check heat exchangers for blockage take off both end caps and look down each tube?
have the heat exchanger pressure tested,


test the new thermostat by boiling it make sure it opens all the way at 160

test motor without thermostat




Old 06-10-2021, 01:22 PM
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Check your gauge and sensor? Get an infrared thermometer and check temps with that as well.
Old 06-10-2021, 02:02 PM
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Originally Posted by 30West View Post
Check your gauge and sensor? Get an infrared thermometer and check temps with that as well.
100x this. Get a temp gun and check all over the engine. Check near the temp sensor.

Also verify your sensor is the right one for your motor and guage.

Old 06-10-2021, 04:05 PM
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Agree with all above.
Has this engine been the same since your friend got it or is this a recent change?
At WOT underway, does the engine reach toward the top of it's spec rpm range , or possibly well below that with engine overloaded due to over-pitched prop?

Confirm you don't have installed a 2-station temp sender with 1/2 the resistance at any given temp. Lower resistance in a temp sender temp equates to higher gauge reading. And do use an IR temp gun aimed next to the thermostat housing and temp sender. when the gauge is reading 200*F . Readings should be very close to the other.

All FW -side hose clamps are tight, no weep at the bottom of the circ pump?

Is the coolant staying at the same level each time when checked cold , or is there overflow to the reservoir or just have to add often with no overflow evident? If overflow at 200*, is the correct pressure cap being used?
Are you sure the t-stat is installed correct side up? Does it have purge holes in the flange? If not you can drill 1 or 2.


Does he have the normally optimum 50/50% coolant to water mix in there ? And have not mixed the old "long life" (Dexcool ) A/F with non-long-life A/F so gelling does not occur? ( Most long-life A/F now says on the label, compatible with all other type A/F.)

If not done already, maybe time for a good flush & drain of the rest of the FW side of the system in spite of the cleaned H/ex.?

Can you tell if the H.ex is same as the original part?. (Similar-size exchangers on the outside can have different "passes" setups on the inside..... but that may lees common on this size engine. ) Or perhaps it is even an aftermarket conversion to FWC ? Is the H.ex mounted so the top is above the engine to better trap circulating air in the coolant for purging?

At least you have confirmed any actual temp problem is not on the RW side with your hand-on-the-riser/elbow basic simple test ( as long as you can keep it there painlessly & indefinitely at any rpm and load. .)
Old 06-10-2021, 04:38 PM
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Yes. Heat exchanger was boiled and tested. Clear as a whistle.
This is 2nd thermostat we installed. I was hoping first one was bad but same thing.
Old 06-10-2021, 04:44 PM
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Check it with a temp gun.
Old 06-10-2021, 04:49 PM
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Originally Posted by TTaxi View Post
Agree with all above.
Has this engine been the same since your friend got it or is this a recent change? Same engine and drive. He just replaced the long block with same specs. (Over 30 yrs this is the 2nd time he replaced it)
At WOT underway, does the engine reach toward the top of it's spec rpm range , or possibly well below that with engine overloaded due to over-pitched prop? RPM range is within spec. Same as always been for 30yrs. Plenty of power. Same prop.

Confirm you don't have installed a 2-station temp sender with 1/2 the resistance at any given temp. Lower resistance in a temp sender temp equates to higher gauge reading. And do use an IR temp gun aimed next to the thermostat housing and temp sender. when the gauge is reading 200*F . Readings should be very close to the other. Since this is a new sender and gauge, I will have him double check. He has infrared gun and I believe he verified it was very close to what the gauge was reading.

All FW -side hose clamps are tight, no weep at the bottom of the circ pump? All tight. No weeping. New impeller.

Is the coolant staying at the same level each time when checked cold , or is there overflow to the reservoir or just have to add often with no overflow evident? If overflow at 200*, is the correct pressure cap being used?
Are you sure the t-stat is installed correct side up? Does it have purge holes in the flange? If not you can drill 1 or 2. No coolant loss. Cap is correct. T-stat installed correctly and is 2nd one replaced. Dont remember if it has purge holes.


Does he have the normally optimum 50/50% coolant to water mix in there ? And have not mixed the old "long life" (Dexcool ) A/F with non-long-life A/F so gelling does not occur? ( Most long-life A/F now says on the label, compatible with all other type A/F.). Basic 50/50 mix. Same as he always used.

If not done already, maybe time for a good flush & drain of the rest of the FW side of the system in spite of the cleaned H/ex.? Its a new engine block, intake manifold and circulator pump. He ran a hose thru the block when circulator pump was removed and flow was fine.

Can you tell if the H.ex is same as the original part?. (Similar-size exchangers on the outside can have different "passes" setups on the inside..... but that may lees common on this size engine. ) Or perhaps it is even an aftermarket conversion to FWC ? Is the H.ex mounted so the top is above the engine to better trap circulating air in the coolant for purging? This is an OE setup. It was fine for first half of last summer after engine was replaced. It started to overheat end of last summer but we think we vastly improved it when we replaced housing on top of outdrive(air was being sucked in when on plane) and all SW hoses.

At least you have confirmed any actual temp problem is not on the RW side with your hand-on-the-riser/elbow basic simple test ( as long as you can keep it there painlessly & indefinitely at any rpm and load. .)
. yes. manifolds never get hot to the touch. You can leave your hand on it all day long.
Old 06-10-2021, 05:24 PM
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Originally Posted by Aussieguy View Post
if bad head gasket
you'll either loose coolant in the closed system or you'll see bubbles in it or Both
how often does the coolant need topping off ? never

did you check heat exchangers for blockage take off both end caps and look down each tube?
have the heat exchanger pressure tested, yes and yes. Clean as a whistle. was boiled and tested too.


test the new thermostat by boiling it make sure it opens all the way at 160 This is 2nd thermostat so I am assuming we cant get 2 bad ones in a row.

test motor without thermostat
We did this last year when it was actually overheating, and it didn't help at all.
Old 06-10-2021, 07:25 PM
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Originally Posted by AlexisMarie View Post
. yes. manifolds never get hot to the touch. You can leave your hand on it all day long.
I expect you meant to type riser/elbows as ex. manifolds are going to be hotter. But if the riser/elbows are that cool he has plenty of flow on the RW side.so ignore that.
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Old 06-11-2021, 06:09 AM
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only other things I can think of.....

air pocket in closed cooling?

too much pressure in the closed cooling?
change the radiator cap
Old 06-11-2021, 08:50 AM
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I would first check the temps with an IR temp gun as several others advised, check right under the stat housing on the intake manifold, I found that this area seems to read closed to the true temp. Also have you ever bled all the air out of the engine, hoses and H/E, an air pocket can cause this problem, consider getting one of the Lisle radiatior funnels, they work well to bleed air out, it can take a while. If you see bubbles in the cooling system, that is a sign of a bad head gasket, it is exhaust gas getting in the coolant. There are testers to check for that as well.


Old 06-11-2021, 10:09 AM
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Record and post the water temperatures entering and leaving the heat exchanger on both the raw and coolant sides.

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