'89 150 Carbed XR4 Uneven Head Temps

Starboard side is running approx. 145* and Port is approx. 120* taken with a temp gun. This is a new to me motor as I've never run it other than on muffs yesterday and today. Also has high WP 12-15 psi at idle with little to none tell tale, it varies, but never has a good forceful flow. WP drops to near normal when tell tale is working, then shoots back up.
Fellow I bought it from says he put in new water pump and both thermostats. I will check both, but the uneven head temps bothers me...as they are not overheated.

Thanks for any helpful direction,

Re: '89 150 Carbed XR4 Uneven Head Temps

I had that problem once, right after I sawed a rotten log in half with the engine. High water pressure indicates plugged water passages. When it gets warm enough for t-stats to open, then pressure will drop. All the water for the tell-tale goes through t-stats first. A strong stream doesn't necessarily indicate good cooling, only that the water pump is working and the engine is warm.

Normally, there's a considerable amount of water exiting the power head before the t-stats. More leaves when the poppet opens up at about 12 psi. T-stats only open up when the engine reaches full operating temperature.

I believe it would overheat under load. You need to get it cleaned out.

I was able to clean out enough splinters to get it back to normal by looking behind the exhaust cover.

Re: '89 150 Carbed XR4 Uneven Head Temps

I had that problem once, right after I sawed a rotten log in half with the engine...

I believe it would overheat under load. You need to get it cleaned out.

I was able to clean out enough splinters to get it back to normal by looking behind the exhaust cover.

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Heh, they make Stihl's for those logs.
Thanks, I'll get to tearing into it. Been reading that those exhaust cover bolts might be a problem breaking and such...

Re: '89 150 Carbed XR4 Uneven Head Temps

Auminer said:

Heh, they make Stihl's for those logs.
Thanks, I'll get to tearing into it. Been reading that those exhaust cover bolts might be a problem breaking and such...

Click to expand...

Good penetrant (pb blaster), some light tapping (shock for the penetrant), and patience, much patience.

Re: '89 150 Carbed XR4 Uneven Head Temps

Ok, here's what I've got, first shot shows the exhaust clearer, second the water ports best. Note the piece of carbon in #2. Also as you can see I have a leaking gasket at the bottom, I believe it is from it running rich. (because the oil tank lid is loose/cracked)

Nothing that says "here's the restriction", guess its on to the heads? The popoff valve wouldn't give me uneven temps.

BTW didn't break one bolt!!

Re: '89 150 Carbed XR4 Uneven Head Temps

Auminer said:

BTW didn't break one bolt!!

Click to expand...

Good Job.

Carbon goes with the territory (big 2 cycle engine)

Re: '89 150 Carbed XR4 Uneven Head Temps

Any place to buy head gaskets without buying the entire gasket $et? I don't see individual head gaskets on boats.net...

Re: '89 150 Carbed XR4 Uneven Head Temps

Sorry 'bout that, I've found them. Back to work...

Re: '89 150 Carbed XR4 Uneven Head Temps

Ok have the heads off and found only minor (IMO) restrictions, two of these "things" in each side. They are approx. the size of an half worn pencil eraser and looks to be seed or egg of some sorts...soft/fragile rubber like shell. NOT a piece of an impeller which I was expecting to find.

Remember this wasn't heating up, but had high water pressure at idle and low flow pee, would this minor restriction in the head cause high pressure? Do I need to look further...where??

Re: '89 150 Carbed XR4 Uneven Head Temps

...any thoughts or input?

Re: '89 150 Carbed XR4 Uneven Head Temps

Well, it seems as the help/knowledge has come to an end here on this subject.

Re: '89 150 Carbed XR4 Uneven Head Temps

Auminer said:

Well, it seems as the help/knowledge has come to an end here on this subject.

Click to expand...

I guess you got that one right.

Re: '89 150 Carbed XR4 Uneven Head Temps

Remember this wasn't heating up, but had high water pressure at idle and low flow pee, would this minor restriction in the head cause high pressure? Do I need to look further...where??

Click to expand...

I'm also guessing you are stumped too.

Re: '89 150 Carbed XR4 Uneven Head Temps

Since I was left hanging on this thread, I'll let others know the outcome as to keeping with the forums helpful policy.

I found the partial restrictions as shown, but the ones leading to high water pressure readings were found in the Poppet
Valve as indicated by this water pressure guide I found searching the forum. I cleared the blockage and installed a Poppet Valve kit.
If I would have been directed to this initially I would not have had to risk taking off the exhaust cover which can very likely lead to broken bolts.
There were no restrictions under the exhaust cover, only in the heads and Poppet Valve.

Speaking of the exhaust bolts breaking, I will add a little help here. It has been correctly stated to use heat, and
moderate hammering and much patience to loosen these bolts. While this is true, it was helpful to me to know just how much
heat is needed or required. The manual states to apply Loctite 271 (Red) to these bolts when installing and torque to 200
inch lbs (which is 16.66666 ft lbs). Well Loctite 271 needs 500*F to melt and the bolts must be removed while heated, so
don't let them cool off prior to breaking them loose. A little tapping wouldn't hurt either.

Hope this helps someone else...

Re: '89 150 Carbed XR4 Uneven Head Temps

I will say thanks for keeping this thread alive as I think I am having a similar issue with my 150. I thought I had found the issue last week but after running the boat over the weekend I have found that I still have an unusual overheat issue. I will say that I have a water pressure gauge coming this week and once that is installed I will be able to do some further investigation. My engine runs fine at idle and the temp gauge sits at 140. At 2,000-4,000 rpm the gauge creeps up until the alarm finally goes off. If I run at above 4,000 up to WOT it sits on 175. Engine isn't too high, water flow on the foot is good as far as I can tell. Water pump new last year, poppet assembly two years ago and new t-stats last week. Jackets were clean at the t-stat housings but I did ingest sand two years ago, thus the water pump and poppet. Maybe I have sand laying in a passage. The water pressure will tell me. I appreciate your posts as they will help me fix mine.

Re: '89 150 Carbed XR4 Uneven Head Temps

Figured someone might need similar help as there are over 300 visits to this thread.
A water pressure gauge is always good to have and I'm curious as to what yours will read. From my limited experience on this motor I'll place my bets on sand in the heads, a relative easy chore providing you are careful and don't twist off a corroded head bolt. (take special care if any appear corroded and work them out, I broke one and had to drill it out) Around $50 or less for gaskets and re-torque to 40ft lbs. The Exhaust cover doesn't need to come off to access the heads. These bolts don't call for Loctite or anything except for a light coating of oil when reinstalling hence there shouldn't be any Loctite to give you problems.
HTH and let us know...