1989 carbed 454 temp issue

[stinger222]

40 hrs on 454, new temp gauge, new sender, new 160 deg thermostat/gaskets/etc,new impeller,new circ pump. started seeing an issue last season where needle will only move slightly up to 120 deg, then it stays there as the boat is driven. Come off plane, gauge spikes up to 180-200, then quickly drops back to 120. Temp gun reads 160 the thermostat housing. Heads/valve covers/intake are hot as they should be, risers cool like they should be. Only part I haven't replaced is the thermostat housing. This orig was a saltwater boat. Could their be an internal leak causing these weird temp readings.

 

[Boat Doctor1]

Something to check?? Should be a rubber hose -on outside under outdrive-sort of "Hidden" unless drive is tilted up. Make sure that hose is not broken, cracked, or split! if so that will cause some overheating as water can be leaking out of that hose & not getting full flow to engine.

 

[alldodge]

40 hrs on 454, new temp gauge, new sender, new 160 deg thermostat/gaskets/etc,new impeller,new circ pump. started seeing an issue last season where needle will only move slightly up to 120 deg, then it stays there as the boat is driven. Come off plane, gauge spikes up to 180-200, then quickly drops back to 120. Temp gun reads 160 the thermostat housing. Heads/valve covers/intake are hot as they should be, risers cool like they should be. Only part I haven't replaced is the thermostat housing. This orig was a saltwater boat. Could their be an internal leak causing these weird temp readings.

Do you have the thermostat housing like the one in the link? If you do, are the check balls still there?

http://www.mercruiserparts.com/Show...bnbr=160&bdesc=THERMOSTAT+HOUSING++NEW+DESIGN

 

[stinger222]

no I don't have the one with the check balls, I have the one that only dumps water into the manifolds, not the risers

 

[tpenfield]

You will see the temperature rise when you go from cruising speed to a slow speed, but it should only be about 20 degrees or so. I would suspect that you are not getting quite enough flow at lower RPM's, but the trick would be to figure out why. Oil Cooler OK and clear?

 

[alldodge]

no I don't have the one with the check balls, I have the one that only dumps water into the manifolds, not the risers

You or someone must have changed them out. The old style for your year is in the link below and it has feeds for both manifolds and elbows. The Tee/valve item in lower left corner, it also has check balls. If the balls have been removed there is no restriction so water will flow out to the elbows and allow the block to not be full of water.


Or do you have another design?

 

[stinger222]

I have a different design. See this link.

http://www.marineengine.com/newpart...454+&+502+cid)+engines&replacement=-8M0061381

 

[alldodge]

I have a different design. See this link.

http://www.*****************/newpar...454+&+502+cid)+engines&replacement=-8M0061381

That link was done away with by iboats (competitor). I'm looking as a 1989, but if you have one which resembles this one then it has been upgraded

 

[stinger222]

that looks like mine

 

[alldodge]

that looks like mine

OK then your engine has been upgraded. This is good, need to find out what style or manifold to elbow gasket your using. If you are using ones with four large holes this could be allowing to much water to pass and not keeping the block full. You should have gaskets which look like this, with the two small holes

Keep in mind I'm guessing at possible issues. My thought is your coming off plane and the water draining off somehow. Issues which are not clear to determine, is the thermostat should keep the block full, the thermostat housing is reading 160 degrees (your IR gun) yet the temp gauge is going close to 200. The temp sender is in the same housing.

 

[stinger222]

Gauge reads about 120 after warmup. but when I point the IR gun at the sender, its about 175 (I'm using a 160 thermostat, water temp is 85). When I turn the boat off, but then turn the key back to "on" position, temp gauge goes up to 200 deg. no way the the temp goes up 80 in 2 seconds. What is going on?

 

[alldodge]

Gauge reads about 120 after warmup. but when I point the IR gun at the sender, its about 175

You know there is a possibility your gauge is the issue.

Also when the impeller was replaced did the housing have any signs of wear. How old was the impeller, reason for asking is there were some impellers made which were not the right size by mistake, This was some years ago but just an idea. The other thing is as tpenfield mentioned, have you checked the power steering cooler for restriction?

 

[stinger222]

I pulled the gauge and it hooked it up to my 71 corvette, works perfect. I'll wire the gauge in the boat with dedicated + wire to the ign switch and a fresh ground to the battery and see if that changes things.

 

[skippy2235]

Same issues I was having, went through 3 T-stats before I found this:
Yes this will fit.
Get this from a good parts store like Napa, carquest ect. Mr. Gasket 4363 Performance Thermostat

http://www.amazon.com/gp/aw/d/B000CM...B2L&ref=plSrch

 

[alldodge]

I pulled the gauge and it hooked it up to my 71 corvette, works perfect. I'll wire the gauge in the boat with dedicated + wire to the ign switch and a fresh ground to the battery and see if that changes things.

Sorry should have mentioned the sender as well, gauge appears to be ok, but the sender feeding the gauge may be the issue. This isn't to say it's not overheating but just want to make sure.

Mr. Gasket 4363 Performance Thermostat

This is a 160 degree stat, the OP should have a 140

 

[skippy2235]

then do a search for 140 they come in all temps. go to MR gasket , com and look.

 

[stinger222]

The sending unit is brand new. I'm wondering if the circulation pump is to blame.

 

[alldodge]

I'm leaning toward exhaust riser gaskets or risers. Something is causing it to loose water to fast and it is not staying full.

I'm wondering if the circulation pump is to blame.

In your first post you said the circulation pump is new

 

[stinger222]

I meant to say the circ pump is not the original, but it has a couple seasons on it, it is one of those GLM ones that are sold on ebay.

 

[stinger222]

I have the 496 manifolds/risers. There is no gasket, the water passes from the manifolds to risers through 2 short 90 deg hoses. I'm with you, its like the sender is not immersed in water, but I know I am pumping tons of water because you can see it coming out of the exhaust, risers are cool to the touch. Engine is heating up to operating temp, but sender is not reading it. When I come off plane, the gauge does begin to rise (the boat levels out and the water rushes to the front of the block) The only old part in the mix here is the thermostat housing. It was orig a saltwater boat, the thermostat housing looks pretty corroded inside. Maybe internal leak is letting cold water hit the themostat all the time before it goes through the block????