1989 5.8 OMC runs hot

[kpoly]

I'm trying to run down why my 5.8 runs hot and I'm focused on seeing if it is getting enough water. When I measure it at the t stat housing, I get about half the amount then if I take a measurement from the gimble housing below ( outdrive is off so I'm putting the 1/2 inch pex tube in the water inlet. Can anyone tell me how much water these engines should be receiving when they are relying on the impeller for delivery? Any other suggestions on where to look is appreciated.

Engine seems to run fine. Replaced exhaust manifolds last year, so that problem is ruled out. I suspect the hose that connects at the gimble housing and goes just inside the transom. Not sure how one inspects this hose without taking the gimble housing apart.

Thanks.

 

[Bondo]

Re: 1989 5.8 OMC runs hot

I'm trying to run down why my 5.8 runs hot and I'm focused on seeing if it is getting enough water. When I measure it at the t stat housing, I get about half the amount then if I take a measurement from the gimble housing below ( outdrive is off so I'm putting the 1/2 inch pex tube in the water inlet. Can anyone tell me how much water these engines should be receiving when they are relying on the impeller for delivery? Any other suggestions on where to look is appreciated.

Engine seems to run fine. Replaced exhaust manifolds last year, so that problem is ruled out. I suspect the hose that connects at the gimble housing and goes just inside the transom. Not sure how one inspects this hose without taking the gimble housing apart.

Thanks.

Ayuh,.... How old is the impeller,..??

 

[Lou C]

Re: 1989 5.8 OMC runs hot

In the shop manual it says with the boat in the water, if you disconnect that hose; hold it up and have someone start the engine, you should get a head of water 2-4" high. If not, you have to check the impeller for wear, the hose and p/s cooler for blockages...
Other things that can cause hot running are bad seals on the water tube in the drive, the gasket for the impeller housing not sealing, exhaust flappers that may have melted in a previous overheat dropping downand blocking the exhaust. Thermostats can stick but usually they stick open not closed. These are high volume low pressure systems, anything that restricts the flow of water in or out will cause hot running. Normal temps are 160-175*F.

 

[kpoly]

Re: 1989 5.8 OMC runs hot

Hooked the engine up to garden hose without the outdrive on. Measured amount of water intake and gets 1 cup after 10 seconds outside the boat but when I measure it at the t-stat housing, the amount of water drops to 1/2 cup for 10 seconds. What's the best way to measure water amount when the boat is out of the water

 

[Lou C]

Re: 1989 5.8 OMC runs hot

I'm not sure what you are asking here but if you want to know how much water the impeller can supply the engine (the only important thing to know here) the only way to do it is the way I described above. You can't do it on the water muffs because they don't supply enough water. If you have a raw water supply issue that's the best way to test. Then if you have a problem you have to go back and see if its a blockage in the PS cooler, leak in the impeller housing gasket, worn impeller/wear plate, bad gaskets for the water tube in the drive (not so simple drive has to be split to check). One last thing is make sure the little hole for the nipple on the impeller housing is open, it allows air out of the impeller housing to make it easier for it to prime.

Put the outdrive back on, put the plug in, back the boat in the water, till the stern floats and test again and post back. If you have enough water there then raw water supply is not your problem.

 

[kpoly]

Re: 1989 5.8 OMC runs hot

I'm continuing to find out why my 5.8 runs hot. Did a leakdown test and it looks as though #5 has a 15% leakage, #6 -20%, #7 - 30% and #8 has about a 35% leakage, enough to make me suspect either a head gasket, head malfunction or a block issue. In my test I noted the heads on this engine have a bolt for the rocker arms that does not adjust rather than than a nut where you make the adjustment with a feeler guage. Did 5.8s have this type of rocker assembly? And do you think 20% leakage is significant?

 

[jerryjerry05]

Re: 1989 5.8 OMC runs hot

What's the compression on the motor.
The non-adjustable lifters are standard on your motor.
Just tighten down and use locktite.
The old manifold?did it leak into the cylinders?

 

[kpoly]

Re: 1989 5.8 OMC runs hot

I don't believe the old exhaust manifolds leaked as I tested them after pulling them off the engine. I did not do a compression check but the engine ran fine when started and there was no water/oil mix noted on the dipstick. The boat is new to me so I do not have a history but I suspect if may have been in salt water. Thanks for confirming these lifters are standard and simply need to be tightened down.