Water Temp--what's too hot?

[kopy kat]

My '99 5.7 EFI w/Alpha 1 runs fine at 3200 rpm or less, but a long run at 4,000 + rpm brings the sometimes working temp gauge up to the 220 mark. No alarms go off, as I watch the guage and bring the rpms back down to 3,000-and the temp gauge drops back to 160-170 area. I'm running a new 160 degree t-stat, and have a new sending unit. Any ideas as to why the temp rise (I can't find a restriction-but my hoses are 5 years old)? thanks, Larry

 

[Lou C]

Re: Water Temp--what's too hot?

That is definitly too hot, you should be running from 160-175 or so with the 160 stat. First place to look is the risers/manifolds. Are you in salt water, if so it may be time to replace them. Often high speed temp rises are due to clogging in the risers, the water can't get out of the engine fast enough. Also it is important to get this under control since the part of the exhaust system that is aft of the risers (rubber hoses) may be overheating as well which is potentially dangerous.

 

[kopy kat]

Re: Water Temp--what's too hot?

No salt---just fresh water-and only about 160 hours on the engine---new heads installed last year ( and the year before as well) so this high rpm heat problem isn't really new--but no one seems to have an answer. Is there a way to check flow rates coming into and out of the total system? Thanks, larry

 

[crazy charlie]

Re: Water Temp--what's too hot?

You can try a 145 degree thermostat.I believe thats what is called for.Check or backflush the power steering cooler.Open the small drain bolts(brass) on the risers one at a time while at idle and push the end of a coat hanger in there and move it around and see if some crud or rust comes out.If it does you can try digging it all out or take the riser off and run muriatic acid through it or replace it.Charlie

 

[kopy kat]

Re: Water Temp--what's too hot?

Hey Crazy Charlie (and to think they make fun of my name)---I checked the risers last year while the mechanic took 8 weeks to replace the heads--they were fine-no rust to speak of. The required stat is a 160---and I did try a 140, but it made no difference on a high rpm run--I think I'll try replacing the hoses this spring, as well as another impeller (is there any chance the main water pump might not push enough water at a higher rpm?)-and if so, how do you test the main water pump? Thanks to all, Larry

 

[cobra 3.0]

Re: Water Temp--what's too hot?

Usually the main water pump will squeel when it's shot and or leak. <br /><br />On mine, I had changed the impeller, sending unit, thermostat, took off and checked the riser and manifold, and flushed every hose possible. Still showewd overheating. <br /><br />I then put on a cheap mechanical auto guage from Wally World and it showed that the temp was fine.<br />So it was my guage that was faulty.

 

[Boomyal]

Re: Water Temp--what's too hot?

I don't have wide experience, but for years my 1975 302 ran right on 160 deg's w/ a 160 deg stat. It never varied more than a couple of deg between idle and a hard run. Several years ago I installed a closed cooling system and installed a 180 deg stat. Same, same. Never varies more than a couple of degrees from hard run to idle.

 

[kopy kat]

Re: Water Temp--what's too hot?

According to my Clymer manual--the t-stat should be fully open at 25 degrees past the setting on the t-stat. Since my t-stat is a 160, add 25 = 185 degrees---isn't this running too hot?

 

[Boomyal]

Re: Water Temp--what's too hot?

185 deg is a much better tempurature for ideal combustion efficiency. The only reason they run 160's and 140's is to reduce the amount of salt that would plate out in a motor. If the motor is never run in salt water there is no need to run that cool. Manufacturers cannot guess where the boat will be used so they install the cooler stat. Auto engines, today, run well into the 200's for emission purposes.<br /><br />That being said, even though a stat may not be fully open until 25 deg past it's rating, they are still intended to hold an engine at the rated temperature, constantly. Motors do not want to keep expanding and contracting during operation.<br /><br />I suggest that you must have issues, related to cooling, that are not allowing your engine to remain at the t-stat rating.

 

[Capt.T]

Re: Water Temp--what's too hot?

I recall someone with a 5.7 L. Mercruiser I/O having an overheating problem and learned that one of the exhaust water flapper valves (located inside of the exhaust pipe) had broken off and lodged near the outlet of the exhaust. This caused a restriction of the exhaust/water outlet and therefore overheated the engine.<br /><br />You may want to check this out.

 

[calwldlif]

Re: Water Temp--what's too hot?

If the valves are adjusted too "tight"<br />heat will build up.

 

[O.P.]

Re: Water Temp--what's too hot?

Had a newly built 350 in a fellow workers truck. He's literally done dozens of intake jobs and head jobs for customers with never a problem. He built his own motor on a stand at the shop and put the intake gaskets on backwards. The coolant passages from the heads on the front should have an opening in the intake gaskets the size of the ports. The rear are closed except for a hole the size of a pencil lead. When he put his on backwards then the coolant couldn't get to the thermostat to properly open it. His symptoms were just like yours. We pulled the thermostat housing and looked down the passages to the heads and saw they were installed wrong. fixed that and fixed his overheating problem. Maybe this could help you.<br />O.P.

 

[Alexo1us]

Re: Water Temp--what's too hot?

I can tell you the temp on my boat runs less then 100 with out thermostat I had a 160 it runs at 160 or less all the time and around 145-150 1000 rpm.<br />A;ex