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Over heating mystery...

A

Alce Deal

Member
Hello Everyone, continuing with my engine rebuild, Volvo Penta AQ231 A, 1989. Engine is running smoothly, how ever; every time I start the engine after been off for few hours the Temp raises to 180 plus within 7 minutes, and the red light temp flashes. Once I turn the engine off for 5 mins, I can then turn the engine back on and if I squeeze the water supply line (hose) from the thermostat housing to the circulating pump for few mins the temp drops down to 149 and stays there, the temp light continues to flash indicating a possible problem. I have removed the thermostat and tested, is rated at 140 and it does open at 140 degrees, I have run the engine without the thermostat and the temp never raises it all. Is it possible that the circulating pump has gone bad? is it normal for the hose that goes from the thermostat housing to the circulating pump to the hot all the time? :confused:
 
All too often we blame the thermostat for an over-heating issue.
I've found that the best way to find out what's wrong, is to start with the entire system from the water intake, and on up and through the entire system.
P of E.... process of elimination... one item, and one item only at a time.

Here's your AQ 231A, shown with the DP drive.

Volvo-Penta-AQ231B-Abbildung.jpg


At the front of the engine, will be your sea water pump..... crankshaft style.
This pump shown is the Johnson F5B-9 (4 front cover screws).
(being shown 180* out of phase)

JOH10-24232-1


Your pump may be a Jabsco (shown below w/ 6 front cover screws), and may have been replaced with the large volume Jabsco.

140.jpg



The large volume Jabsco impeller measures 1.990" in depth.
The large volume Johnson (F6B-9) impeller measures 1.900" in depth.

The two impellers look almost identical, and the F6B-9 impeller will fit into the large volume Jabsco pump body.
The lacking .090" difference in impeller depth, will play Hell with you.

If by chance you have the Jabsco pump (6 front cover screws), verify that you have the correct Jabsco impeller for it.
Parts counter people get this wrong more often than they should! :mad:

*******************

OK.... if that's not the issue, look at the two pump body thrust surfaces.... one is the cover, the other is deep within the body.
These surfaces must be nice and flat.


Next, look at the water neck fitting. These are a routine replacement item.
One small suction breach here.... and your sea water pump will have trouble pulling water in.

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Hello Ricardo thanks for your reply, I checked the numbers of the old pump and the new pump, its a match exactly, for screws pump; I also replaced the neck fitting during the removal and replacement of the engine. I tried the engine again today, same thing, within 7 mins the engine overheated to 190, turned the engine off for one minute, tried again the temp dropped down to 149 and maintained there for 30 mins, low idle 600-700 RPM, you think I may have the thermostat upside down? am trying to find an schematic or sketch to see if the spring goes down or up. Thanks.
 
Have you aimed a laser style heat gun at your engine to check against your temperature gauge?
It may be possible that you do not actually have an over-heating problem, but rather a faulty sender or instrument.

Infrared_Gun.png
 
Possible it's the circ pump?
You in fresh or salt water.
Is it the original?
If not original and your in salt water it could be eaten by salt water.
Is the plate on the rear of the housing stainless?
Not SS then it's probably not original.
The pump itself.Original?
Inside the pump is a cam.
It's what bends the blade and makes the pump pick up water. It's held in place by 1 screw.
These wear down and will pump just not enough??
 
I'll take liberty here and will clarify something, if I may.

The circulating pump is the GM pump on the upper front of the engine. For the raw water cooled engines, this must be the Marine version with the SS rear cover, bronze or SS impeller, and special ceramic shaft seal.
Some people will replace this pump with the automotive version. This works for a Closed Cooling system engine... but not for a raw water cooled engine.

Here is an automotive circ pump kit.
The Marine version pump will use the above mentioned parts.

195519561957WaterPumpRebuildKit.jpg




The Sea Water pump (the pump at the crankshaft), is the pump with the impeller cam.
As Jerry said, look at the cam for wear.
Also look at the two impeller thrust surfaces. There can be no deep scoring at these surfaces.


This is NOT your exact pump, but is similar with regard to the impeller cam and the thrust surfaces.
 

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Hello everyone, Thanks for all your reads and replies; After conducting some home testing and removal and reset thermostat housing numerous times, came to the conclusion that the thermostat was upside down. Things were not making sense, new raw water pump (original kind), temp raising rapidly to 190 within seven mins, turning the engine off for 1 or 2 mins, re-start the engine again after the 2 mins and temp would drop down to 149 steady. Removed the thermostat submerged in broiling water spring and cup down = 16 seconds to open at 140 degrees temp, thermostat submerged in broiling water spring up cup up filled with cold water to simulate cold engine conditions = 36 seconds to open at 140 degrees temp, Results compared with a new thermostat without cup = similar. Unable to find a 140 thermostat without cup I proceeded to install a thermostat rated at 160 degrees and wualaa -- engine temp raised to 160 degrees and remained the same without ever passing that mark, Temp warning red light remains flashing starting at 148 degrees. Evidently, the old raw water pump was pumping very slow prior to fail which allowed the water to raise and heat the thermostat from above, the new pump pressure would not allow the cold water above the thermostat to warm up therefore preventing the thermostat from opening... I still need to find a thermostat rated 140 degrees without a cup in order to fit in the thermostat housing spring down. Is kind no embarrassing since am not a mechanic by trade evidently I caused the problem, few years ago, the old thermostat housing broke few years ago and I replaced with a new housing I got from my local dealer and I was told that it was an original part, the housing came with the thermostat which is a cup kind instead of a disk kind and the thermostat only fits in the housing with the spring up... Am curious if any of you have seen this happen before? also, since the thermostat I installed is rated at 160 degrees I will need to find one for 140 degrees that will stop the red warning light from flashing, (my boat has warning temp and a temp gauge). I was just told by my local dealer that all thermostats are rated 160 degrees now days, my question is would it be wise to try to find a 140 degrees? Thanks everyone for all your comments and help...
 
If your boat is operated in fresh water, 160 is OK, else if in salt or brackish, needs to be 140. Re: your dealer and " all Tstats are 160".... Don't think so. 140 is default for sea water cooled engines, 160 for those with a heat exchanger.
 
sandkicker said:
If your boat is operated in fresh water, 160 is OK, else if in salt or brackish, needs to be 140. Re: your dealer and " all Tstats are 160".... Don't think so. 140 is default for sea water cooled engines, 160 for those with a heat exchanger.
Click to expand...
Yes.... I agree!

This is a common misnomer that Raw Water cooled engines need the 140* thermostat.
If in river/lake water, keep your engine temp up.... raw water cooled or closed system cooled.

The reason for the 140* thermostat is due to salt crystallization that begins to occur at/near 143*.
There are no dangerous levels of salt in River/Lake water.


.
 
RE: "If in river/lake water, keep your engine temp up.... raw water cooled or closed system cooled."

You will get notably better fuel consumption at the higher engine temp. I once had a new 318 that I bought from a distributor w/FWC. They left the 140 t'stat in it. I ran it that way for a month and then after determining that my water temp gauge was correct, replaced the t'stat with a 160 one. Instant improvement in fuel consumption. Also at the higher temp, water condensation in oil ( somtimes shows as yellow crud in the rocker covers) is supposed to be less of a problem.

Worse thing you can do is the remove T'stat completely. Internal combustion engines need to run as hot as possible ( within design limits) to run their best. As Ricardo mentioned, salt deposits a big issue with high temp t'stats in salt. I saw this in my HONDA OB when a dealer gave me a miscataloged t'stat. plugged up passages in just a couple of hours of operation. Will never install a t'stat again without the old pot on the stove with thermometer test!!!
 
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