Warm-up rate for larger engines

[rationull]

Prior to now I've always driven cars with smaller engines, but we've recently acquired a 99 chevy suburban 2500 with a 7.4 V8 to use [very] occasionally to tow a horse trailer. Last weekend we drove it around a little to get a feel for it and give it some road time before getting it ready for towing, and the engine's behavior with respect to temperature got me a little concerned.

For a while on the highway the temperature was staying pretty low. It was below the middle of the dash gauge, and according to my scangauge it was just barely breaking 140 to 150 degrees for a while. In stop and go driving, it eventually rose to 175 or so but it would still cool down a bit if not stressed after that. I'm not sure if the t-stat is a 180 degree or a 160 degree.

The other cars I've driven, esp my 07 civic (which is the only other car I've monitored w/ my scangauge) reach operating temperature relatively quickly and have no trouble staying there.

At first I assumed the suburban's t-stat was bad, but since the temperature eventually did get up to a reasonable range I'm not so sure anymore. I realize that since it's a large engine with excess cooling capacity (for towing) it's probably going to run pretty cool when it's not stressed, but I just wanted to ask here if anyone w/ more experience with larger engines recognizes this as normal or if there might be some problem.

 

[wapacz]

in the middle of the winter my 95 gmc 1500 with a 5 liter takes about 2 to 3 miles on the express way to get up to heat. Then the cooling system opens up and it drops fast about 50 degrees then climbs back up over the next mile or so to 190. Thought I am pretty sure that it doesn't get as cold there as it does here.

 

[Shannow]

V-8s (particularly iron blocked V-8s) have a lot of metal and water to get up to temperature.

 

[SevenBizzos]

Geez.

My 4.6 took nearly 10 minutes of drive time to warm up when I was driving it in the winter. Somewhat annoying. I can only imagine with a larger engine than that would be longer than that.

Bigger engines take longer to warm up.

 

[BuickGN]

I think iron vs aluminum is the biggest factor. My GN (iron block)takes 10 minutes to warm up with an easy morning drive. When I put aluminum heads I could swear it warmed up faster but I changed so many things it's hard to tell. The TL takes about 2 minutes to hit full water temp on a 35 degree day if I drive it right away but it's putting out heat within 45 seconds.

 

[Gary Allan]

My 4.0 cast iron warms faster then my aluminum head engines (when I had them) ..but this is due to the bypass rate of the cooling system. I think the radiator circuit "also runs".

That said, you shouldn't have trouble reaching op temp. It may take you a while, but you should reach it. Change the thermostat.

 

[Shannow]

When I was mucking around with lower hose thermostats on V-8s (and later a 4), it was possible to run 8 miles to work (3/4 of that highway) with a dead cold top tank on the radiator.

The block surface area and heater were more than enough heat rejection surface to keep water from making it to the radiator.

 

[rationull]

Hmm. I should take the truck out again and watch this more closely to verify what I'm seeing. It sounds like the thermostat might be going bad, but I've never had one "sort of" fail on me before.

I'm pretty sure this is an iron block engine. Not sure about the heads but I assume they're aluminum. I'll take it out tomorrow morning on a highway drive and pay more specific attention to how the temperature trends.

 

[mechtech2]

160 or even 180 is not what I'd choose.
I'd go higher, like 195 for fuel economy and engine wear.
If the engine needs more cooling, any thermostat is open fully anyway.

 

[dwendt44]

A 160° thermostat is unlikely. Hard to find and most folks wouldn't even think of it.
180° are almost as hard to find; around here, you have to order them out.
Wouldn't hurt to change the thermostat, 195-198° are what the factory put in. The gauge on the dash could be off, I've known several GM products that read low.
The size of the radiator/cooling system shouldn't matter as the theromstat would just shut down the water flow until it's near it's opening temp.

 

[rationull]

Good to know. The only reason I thought it might be a 160 was because of where the temperature seemed to be hovering. Like I said I'm going to have to take it out tomorrow and do some more careful observation. If I do end up replacing it (which I probably will) then I probably would go for a 195.

I'm not going off the dash gauge, btw (I'm not even sure if that gauge even has any number on it). I was using my scangauge, which presumably pulls from a reliable source.

For what it's worth, the colder thermostats are probably a little easier to find out here, since it gets relatively hot sometimes.

 

[Doug Hillary]

Hi,
I have done extensive temperature monitoring on Porsche 928's V8 engines

As Shannow points out some engines, such as the Porsche V8 mentioned (AluSil structure), generate sufficient heat rejection to only have an occasional "bleed" into the radiator if any.
This is especially so at around The occasional coolant bleed as the system reaches equilibrium ensures that no thermal shock occurs as the coolant's thermostat finally fully opens. On the way, the oil's intercooler also heats the lower part of the radiator
Of course air flow on these engines is regulated by an air flap system (fully closed, 30%, 70% fully open) and fully variable fan (twin) speeds - all "computer" controlled
Even at an ambient of 35C and on the open road it is common to have the flaps at only 30% open and no fans on!

The process from a cold start until the operating "core" temperature is attained takes from 15 to 30minutes depending on the ambient

In heavy trucks this process also takes around 20 to 30 minutes

Typically, the lubricant trails coolant from a cold start by up to 20C until the core temperature is stabilised

This helps to understand why engine manufacturers have been using 5w-XX and 0w-XX lubricants for some time now

Regards
Doug

 

[rationull]

Thanks Doug, great information. If it takes 15 or 20 minutes of driving to get to operating temperature for this 7.4 then it's possible the thermostat is fine. Although I'm not dealing with truly cold temperatures here. I'll find out tomorrow.

One question though.. if I do end up getting a new t-stat, I assume OEM (AC Delco?) is the way to go, right? Is something like a Stant OK if I want to avoid going to a dealer?

 

[Doug Hillary]

Hi,
rationull - Yes, IMHE I would always use an OEM thermostat!

I do my temperature checks using a IR reader

On any engine "family" there are always key points to log the temperature(s) from. Consistency is the trick in each case

Regards
Doug

 

[BuickGN]

I guess I'm one of the rare ones running a 160 degree thremostat. Wouldn't think of it in the Acura but I'm not concerned with the extra engine wear associated with it in the Buick and the detonation resistance makes it worth it. Unfortunately, even with the water at a full 160 degrees, the heater doesn't get hot enough on cold days.

 

[eljefino]

I bet you have a 160 in there. Lots of "old school" types wind up working on these things.

 

[Doug Hillary]

Hi,
most Euro car manufacturers appear to seek a "core" operating temperature of around 91-96C. It is common to have a bulk oil temperature of around 100C - however, much depends on the metallurgy used and the engine's application

Regards
Doug

 

[another Todd]

You should have at least a 195 thermostat, maybe a 202. In any rate after a few miles the temp should be up to the thermostats temp rating and not go below that the rest of the trip no matter what size your radiator is. If the radiator cools the coolant way down the thermostat should close building the heat back up. So, I would say your first thought was correct, you have a bad thermostat (as in stuck open or unable to close fully).

 

[rationull]

So after some more careful observation (and a trip that didn't involve so many stops with only short drives between them) my conclusion is that the thermostat is fine, and it's a 160. After 10 or 15 minutes of driving the temperature stayed at 161 according to the scangauge.

The drive I based my original post on was a poor sample in that it was much shorter and for a relatively large percentage of it we were either making long stops at places close together, or going down a very large hill (which tends to delay warm-up even on my civic, depending on the temperature).

So now I'm wondering whether I might as well just run the 160 that's in there until it goes bad, or whether I should get an OEM 195. Any strong opinions? Seems like the going opinion is that a 195 would be better, which I totally agree with, but is it really worth replacing a working t-stat just because it's a 160?

 

[Propflux01]

Yes, it is worth it.