Low RPM Enging Load Causing High Temps
Thread Starter
Burning Brakes
Joined: Aug 2006
Posts: 878
Likes: 2
From: BC
Low RPM Enging Load Causing High Temps
Now this might be a bit of a stupid question as I've not cheked the tuning since going doing a manual swap but I've noticed a trend with my temps when cruising that worrys me slightly.
If I'm cruising with the engine loaded up say 6th gear at 60 (ZF6 with 3.07) and doing around 1600rpm, although the engine feels happy and is not lugging or bucking, I've noticed that the water temps seem to rise rather quickly.
Its floating around the 2-6degree C over here at the moment and most of the time my temps are around 180-190f but left to load as said above I have seen 225f before I switched to a lower gear. As soon as I do the temp comes straight back down.
What I want to know is, could this be something to do with my tuning or am I just spinning to low an RPM for the waterpump to be able to cool effieciently?
If I'm cruising with the engine loaded up say 6th gear at 60 (ZF6 with 3.07) and doing around 1600rpm, although the engine feels happy and is not lugging or bucking, I've noticed that the water temps seem to rise rather quickly.
Its floating around the 2-6degree C over here at the moment and most of the time my temps are around 180-190f but left to load as said above I have seen 225f before I switched to a lower gear. As soon as I do the temp comes straight back down.
What I want to know is, could this be something to do with my tuning or am I just spinning to low an RPM for the waterpump to be able to cool effieciently?
Safety Car
Joined: May 2002
Posts: 4,659
Likes: 82
From: Toronto ontario
timing could be too high. WHat tune do you have in the car ? Generally speaking higher load = lower timing. So, I am guessing here but if you have a tune for a 6 spd car in yours (In which i am guessing used to be an auto and is now a 6 spd) the rear gears may be too steep since the 6 spds come with 3.45 (or 3.54 i forget).
When timing is too far advanced and engine load is high ( or lugging in a high gear at low rpm ) the engine can overheat yes.
When you are cruising at freeway speeds do you notice you are putting your foot into the pedal slightly to maintain speed?
Last but not least 6th gear was designed for cruising speeds with a 3.45 rear axle ratio. Having a 3.07 i wold suggest using 6th over speeds of 75-80 mph or so.
When timing is too far advanced and engine load is high ( or lugging in a high gear at low rpm ) the engine can overheat yes.
When you are cruising at freeway speeds do you notice you are putting your foot into the pedal slightly to maintain speed?
Last but not least 6th gear was designed for cruising speeds with a 3.45 rear axle ratio. Having a 3.07 i wold suggest using 6th over speeds of 75-80 mph or so.
Last edited by 5abivt; Jan 21, 2009 at 11:58 AM.
Safety Car
Joined: May 2002
Posts: 4,659
Likes: 82
From: Toronto ontario
Also when you are on the highway and it starts getting hot, pop the hood and feel all the hoses. Check to see if they are hot or cold. Careful of the fans if they turn on but try to feel if the rad is getting warm. Also have you used dex-cool coolant by any chance? Lots of people mistakenly put it into gm cars that use the green stuff because it says GM on the coolant. You may have sludge build up in the system somewhere preventing coolant from flowing at low rpms where the pump isnt spinning so fast. 
Race Director
Joined: Apr 2003
Posts: 17,700
Likes: 1,667
From: moraga ca
timing could be too high. WHat tune do you have in the car ? Generally speaking higher load = lower timing. So, I am guessing here but if you have a tune for a 6 spd car in yours (In which i am guessing used to be an auto and is now a 6 spd) the rear gears may be too steep since the 6 spds come with 3.45 (or 3.54 i forget).
When timing is too far advanced and engine load is high ( or lugging in a high gear at low rpm ) the engine can overheat yes.
When timing is too far advanced and engine load is high ( or lugging in a high gear at low rpm ) the engine can overheat yes.
Le Mans Master
Joined: Dec 2004
Posts: 5,789
Likes: 8
From: Myrtle Beach SC
St. Jude Donor '05-'06
Engine running lean will cause some heating issues too. I do not consider a moving car running at 225 normal. Even in traffic mine rarely hitts 210. I am guessing WP.
Melting Slicks
Joined: Feb 2008
Posts: 3,286
Likes: 6
From: Palm Beach
The fans don't run at highway speeds. My LT4 does not run hotter in cruise in 6TH. A cooling system tuneup may be in order.
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Race Director
Joined: May 2001
Posts: 14,165
Likes: 9
60 MPH in 6th gear with a ZF pushing 3.07 rear is only turning 1200 RPM's. My guess is that although the engine makes plenty of torque that low, it was never really designed to be operated under heavy load at that RPM. My guess is that your water pump simply isn't flowing enough at that RPM to keep it cool.
Step it up to a 3.45 rear like it was designed for, or install an electric water pump, or both.
Step it up to a 3.45 rear like it was designed for, or install an electric water pump, or both.