Temp Rise at idle

flaMtneer · **Posted:** Tue Sep 13, 2011 7:56 am

Hey - '99 VP 5.7L Gsi/Sx, 234FS. Had head gasket replace + valve work + thermo, circ pump, water pump, etc done this summer which probably makes me paranoid, but it seems I'm getting more temperature rise at idle after running then I used to. When I'm on the throttle temp gauge goes right to 175 and stays rock solid there, but when I drop to idle it rises up into the mid-190s. If I've been pulling the tube or kneeboard it might push after returning to idle. Does this sound normal? Mechanic says he thinks it is, but would have to schedule back in to check.

I feel kinda stupid because in all the years I've had the boat I never noticed or paid that close attention to the differences in the temp and I don't recall it jumping up this high.

ric · **Posted:** Tue Sep 13, 2011 8:11 am

flaMtneer wrote:

Hey - '99 VP 5.7L Gsi/Sx, 234FS. Had head gasket replace + valve work + thermo, circ pump, water pump, etc done this summer which probably makes me paranoid, but it seems I'm getting more temperature rise at idle after running then I used to. When I'm on the throttle temp gauge goes right to 175 and stays rock solid there, but when I drop to idle it rises up into the mid-190s. If I've been pulling the tube or kneeboard it might push after returning to idle. Does this sound normal? Mechanic says he thinks it is, but would have to schedule back in to check.

I feel kinda stupid because in all the years I've had the boat I never noticed or paid that close attention to the differences in the temp and I don't recall it jumping up this high.

When you say drop to idle, you mean instantly it rises, or it rises while sitting there idling for longer then 5 minutes?

acguy · **Posted:** Tue Sep 13, 2011 9:08 pm

I would verify the temp with an IR thermometer, don't trust the gauge there is room for error

flaMtneer · **Posted:** Wed Sep 14, 2011 6:27 am

ric: No, I don't think it's instantly...I'd say over a couple, maybe a few, minutes. When I get back on the throttle, it's almost instantly that it cools back to 175ish.

ac: I don't trust the gauges either, at least not for absolute. It's the difference between the running vs idle reading that concerns me.

Edit: Just re-read my initial post and left out a important fact: Meant to say" If I've been pulling the tube or kneeboard it might push 200 after returning to idle"

M3eater · **Posted:** Wed Sep 14, 2011 7:01 am

With all that you have provided (parts replaced and symptoms), I'll add some thought to the good suggestions, so far.

* There is the possibility of a voltage problem at the gauge. This would typically be due to a poor ground or a system voltage issue (alternator). However, the description of your symptoms does not really fit this issue.

* If your exhaust risers are partially clogged (rusted), this could fit into your current symptoms.

flaMtneer · **Posted:** Wed Sep 14, 2011 7:10 am

M3eater wrote:

With all that you have provided (parts replaced and symptoms), I'll add some thought to the good suggestions, so far.

* There is the possibility of a voltage problem at the gauge. This would typically be due to a poor ground or a system voltage issue (alternator). However, the description of your symptoms does not really fit this issue.

* If your exhaust risers are partially clogged (rusted), this could fit into your current symptoms.

Thanks for the reply. I had the risers and manifolds replaced a couple years ago - so I've assumed they're ok. Maybe that's a bad assumption.

M3eater · **Posted:** Wed Sep 14, 2011 7:12 am

In that case, they "should" be fine.

ric · **Posted:** Wed Sep 14, 2011 9:40 am

Maybe you sucked something up in the inlet or the water pump rubber got damaged (sand from shoring, etc).

When tubing my boat will get to 200*, but if i cruise around for about 3 mins its back down to normal.

Paul I. · **Posted:** Wed Sep 14, 2011 10:02 pm

flaMtneer wrote:

Hey - '99 VP 5.7L Gsi/Sx, 234FS. Had head gasket replace + valve work + thermo, circ pump, water pump, etc done this summer which probably makes me paranoid, but it seems I'm getting more temperature rise at idle after running then I used to. When I'm on the throttle temp gauge goes right to 175 and stays rock solid there, but when I drop to idle it rises up into the mid-190s. If I've been pulling the tube or kneeboard it might push after returning to idle. Does this sound normal? Mechanic says he thinks it is, but would have to schedule back in to check.

I feel kinda stupid because in all the years I've had the boat I never noticed or paid that close attention to the differences in the temp and I don't recall it jumping up this high.

Not to be harsh, but you don't use the words "raw water pump" or "impeller". The impeller was changed out, right? Because, thats what it sounds like to me. More so since the manifolds were replaced a few years ago.

flaMtneer · **Posted:** Thu Sep 15, 2011 7:07 am

Paul I. wrote:

flaMtneer wrote:

Hey - '99 VP 5.7L Gsi/Sx, 234FS. Had head gasket replace + valve work + thermo, circ pump, water pump, etc done this summer which probably makes me paranoid, but it seems I'm getting more temperature rise at idle after running then I used to. When I'm on the throttle temp gauge goes right to 175 and stays rock solid there, but when I drop to idle it rises up into the mid-190s. If I've been pulling the tube or kneeboard it might push after returning to idle. Does this sound normal? Mechanic says he thinks it is, but would have to schedule back in to check.

I feel kinda stupid because in all the years I've had the boat I never noticed or paid that close attention to the differences in the temp and I don't recall it jumping up this high.

Not to be harsh, but you don't use the words "raw water pump" or "impeller". The impeller was changed out, right? Because, thats what it sounds like to me. More so since the manifolds were replaced a few years ago.

Yes the impeller was replaced - twice I believe. (It's a long story.) I'm not even sure this is a problem which is what I'm trying to get a feel for...how much temperature rise should I expect after returning to idle after running on plane, pulling tubes, whatever? If the answer is "None" then there is definitely an issue, if the answer is "Some", then how much is too much?
Thanks.

ric · **Posted:** Thu Sep 15, 2011 8:28 am

I see a rise when pulling but.. I also always do a "cool down" cruise after running hard to cool the engine down. What you're seeing is common in the car world: Heat soak.

After pulling tubes and going nuts, collect the passengers out of the water and cruise around at minimum plane RPM for 5 minutes to cool down the sucker (one song on the radio). Your engine will last longer anyways. It shouldn't rise temp going to idle after.

Also put your blower fan on too when running hard. It will help circulate some cooler air in there as the engine compartment can get very hot.

If you're pulling tubes like a madman (what I do haha) and just sitting there at idle after screaming around at 4500rpms without coolin it down first, yes your temp will rise. The engine has the heat from going 4500rpm and you just slowed it down to idle. The water circulation at idle is nothing compared to what it was seconds ago and with the instant drop of water flow with all that heat = temp will go up.

LouC · **Posted:** Thu Sep 15, 2011 7:56 pm

With my boat (88 4.3 OMC) and a 160 thermostat, it normally ran between 165-170 and would heat maybe to 175 after running on plane, but recently it was running at 175 to start, and heating to 185 after running on plane. After some investigation, I found that one of the manifolds was starting to clog and the water intakes on the outdrive had barnacles in the water intakes. After cleaning them out and replacing the manifolds it's back to normal temps, 165 or so and heats up to 175 after running on plane. I know many boat temp gauges are not that accurate, and some are hard to read because of how the #s are spread out on the gauge. So verify temps by using an IR temp gun at the base of the intake manifold right under the thermo housing. I think heating to 200 after running on plane, is too hot. I'd be looking at the raw water pump and any restrictions in the raw water system. If the raw water pump pulls in air (can be checked using clear hoses spliced into the raw water pump hoses) the same thing can happen.

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Temp Rise at idle

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