View Full Version : Thermostat or Temp. Guage Problems !!!

08-24-2004, 07:57 PM
After being out on the water for about 3 hours today I noticed that the temperature was running low (about 130 F). This happened after we had been barefooting for a while and had stopped for a half hour then we were gonna do some wakeboarding and upon starting i noticed the temp was low. I thought maybe it was because the boat had been sitting and cooled down, but in never cools down that fast or low. After pulling one wakeboarder for 15 min or so the temp didn't change.

So my first thought was that the temp guage was broken. But on close examination i can see that the needle does go up and down about 10 degrees or so. After running fast and stopping it shows heat soak but the temp never goes up more than 130, then after idleing it goes back down to 120.

So now i'm thinking that maybe the termostat/s are stuck. Would this cause the problem i'm seeing? I figure running too low of temp isn't a good thing. If anyone has any input on the situation please let me know. I will also be looking through the other threads to find out if anyone else has talked about this.

Oh and one more thing, after every use i bring the boat back and flush it. When i do this i always feel the water that comes out of the exhaust and today i noticed that it felt cooler than it usually does.

My boat is a 94 Prostar W/ LT1 engine. Thanks for all the help and if you know any threads that have anything that talks about this please point me in the right direction.


08-24-2004, 09:17 PM
Search for "overheats" or on variants of LT1 (LT-1; LT/1) over at the old forum (as well as here) and you'll find TONS. You probably have a stuck open 'stat..

08-24-2004, 09:40 PM
Thanks, I've done a bit of that and found most of them, none for too cold though :mad: However, I talked to a mechanic I know who is very familiar with the LT1 engine and as soon as i described the problem he said it was the top stat. So i will pick one up and install it tomorrow then test it out. But if anyone else out there has any more input please let me know, i'd appreciate it very much.


08-24-2004, 10:15 PM
When you pull the 'stat out, if you launched an impeller recently and lost one or more of the vanes, you probably will find it stuck in the thermostat.

08-24-2004, 10:34 PM
Got the stat out. Nothing lodged in it. I also tested the stat and it started to open (1/16-1/8 in.) at about 125 F and was fully opened around 160-165 F. Is this normal? My second thing to try is the lower t-stat, by the way is this located under the triangular shaped cover? I will check the lower if the problem isn't solved after i replace the upper stat.

Thanks for the info, I will post any results if/when they occur.


09-08-2004, 09:33 AM
Nathan. We are talking about a similar problem in a new post titled, Temp Gauge. My 88' is behaving similar, and can't seem to figure it out. Gauge says 130 when I fire it up, and drops down to 100 instantly. Could it possibly be running this cold? What are your most recent findings? Was the problem solved?


09-10-2004, 01:45 PM
I solved my problem by replacing both of the thermostats (it's an lt-1). I also had to clean the debris from my tranny cooler. Now its running about 170, a bit hotter than usual, but i'm not worried.

09-10-2004, 04:55 PM
did you replace them w/ thermostats from any auto parts store or get the MC ones? 170 seems a little hot??? My LT1 starts runnning strange around 185. What does the temp raise to during the "heat soak"?

09-10-2004, 05:54 PM
Nate- did one of the new 'stats have 1 or 2 small holes in it? If not, you need to get the right one in there. The hole(s) bleeds a little water into the water jacket to keep the temp stable.

09-11-2004, 08:51 PM
I drilled the 2 holes in the top tstat myself. I'm thinking about making them a little bit larger to bring the running temp down to 160. I've checked the water pump and its pulling in plenty of water, anyone have any other ideas as to why i'm still running a bit warm?

09-11-2004, 08:53 PM
Oh yeah, during heat soak the the highest temp i've seen was just under 220, but thats after i drive hard and cut the engine completely. If i'm driving regularly and just slow down to idle then the temp never goes above 180.

09-11-2004, 09:06 PM
Did you drill the holes the same size as the original ones? They're that size for a reason. Too much cold water and the motor won't be at the preferred operating temperature. The normal fuel mapping is based on the temp being in a certain range. Too cold and it runs rich, too hot and it's too lean, leading to detonation and meltdown. Buy the right parts and don't try to make them yourself.

Did you check the bleeder hoses and fittings yet? Also, in another thread, someone had a circulating pump that went south and wasn't moving enough water so you should look into that, too, since his was a similar vintage.

09-12-2004, 09:40 AM
I made the holes the same size (i ordered the tstats from skidim, they told me the size to make them), and i've checked out the pump as well and that seems fine. Whats this about bleeder hoses?

09-12-2004, 10:25 AM
Do a search here for LT-1 overheats. The small rubber hoses going from the heads to the exhaust manifolds bleed air out of the cooling water. If these are clogged, they can't and the motor runs hot.

09-12-2004, 11:31 AM
Okay, thanks. I'll give those a check today.