Thermostat Question

coltarms · Post by **coltarms** » Fri Dec 01, 2006 9:58 am

My temp gauge hardly ever goes above the line for cold. The only times I've ever seen it come up to "warm" is on a really really really really hot day (like 98deg-ish) or when the car is idling in my garage for 20min. It also seems to have an issue with the heater, as in the heater doean't seem to put out any heat.....except that it does great when the temp gauge is showing warm. I understand the principles of a coolant loop and how the heater core works, etc. My question, however, is in regards to the thermostat. If the thermostat was just blown out, as in stuck open, coolant would be flowing at max flow capacity all the time. This would mean that the heat generated by the engine would be transferred away very efficiently, and the heater core wouldn't really have any heat to radiate out. But my understanding was that eventually (like 20 min or so) max engine temp and subsequently max coolant temp would be reached and the thermostat, if properly functioning, would be all the way open anyway. I know my temp gauge works, as I have seen it respond in the garage. I have even seen it respond correctly then the radiator fan kicks on. Ignition timing is perfect. I've set it and checked it many times, and it never goes out. Coolant was drained during the timing belt change (pulled the radiator), and replaced with Propylene Glycol instead of Ethylene Glycol (eco-friendlier.)

So now to the questions:
1. Will the thermostat open and close continuously during engine operation or will it eventually just remain fully open?
2. Could this lack of intended engine operation temp be affecting my vaporization significantly enough to kill mileage and/or affect the EGR operation?
3. Could the Propylene Glycol mixed with the ethylene glycol residue have eaten the Thermostat?
4. Anyone else ever have this issue?

Dave
Hillsboro, OR

Typrus · Post by **Typrus** » Fri Dec 01, 2006 10:46 am

Our cars are Ethylene Glycol only approved. Thermostats, gaskets, etc will be chewed at by anything else. Could be part of your problem.

They can get stuck open. Unfortunatly they can get stuck closed too.

It will open and close based on heat. If it just opened and stayed that way, the engine would lose a lot of heat and thereby mileage. It closes when it gets cool enough, opens when its hot enough. It is a thermo-stat. The spring is a thermostatically controlled metal. It expands with heat, opening the valve, contracts with cool, closing it. It has a pre-set temp it functions at.

Cold=power (unless to cold to combust efficiently)
Hot= economy (untill things blow up and or warp)

I'd recommend either a new thermostat or to try that electronic pump/heat control we were talking about a while ago.
And FULLY flush the system and put in Ethylene Glycol. It won't hurt the environment if it isn't leaking into it.

coltarms · Post by **coltarms** » Fri Dec 01, 2006 11:14 am

Thanks for your input on the thermostat, noted. Time to check it out I guess.

As to the issue of propylene compatibility, ethylene is much more toxic and corrosive than propylene. I have been google searching this for about an hour now and found that all roads lead to propylene being fine, but that mixing the two is a no-no. Here at work we switched to propylene 8 yrs ago in out HVAC units due to workplace safety and the toxicity of ethylene. No issues to date except that the propylene needs to be changed out more often than the ethylene did. Ethylene also tends to create a film that hardens over time, blocking small passages. This is why euro cars (BMWs) now use propylene. I immagine a flush and a new thermostat is definitely the way to go though.....

coltarms · Post by **coltarms** » Fri Dec 01, 2006 5:10 pm

Well, I flushed the beejeezus out of the system. That engine block drain is pretty messy. I then pulled the thermostat and found that it was stuck open. There was no black residue in the coolant. No oil residue either

Just the normal offwhite scale residue in the reservoir and in the radiator. I put in the new t-stat and gasket and filled her up with about 70% water and 30% Propylene Glycol. It rarely gets below freezing here, and it'll be flushed again with radiator cleaner in the spring.

My temp needle comes up about 1/3 of the way within 5 minutes of starting the car and steys there for all conditions!!! I even have heat!!! Hopefully we'll see a mileage increase!

keith · Post by **keith** » Fri Dec 01, 2006 6:14 pm

A lot of people confuse Propylene Glycol with Dexcol. Propylene Glycol is fine in any coolant system, it can mix with Ethylene Glycol, but not recommended. Dexcol is Ethylene Glycol with a different additive package for detergency and corrosion protection.

Unlike Ethylene Glycol, you can run concentration above 67%. I ran 80+% in a car a few years ago. There are some race cars that run 100%. The higher the concentration, the greater the protection from freezing, boiling and corrosion.

The down side of Propylene Glycol is that it tends to trail its Ethylene Glycol counterparts in corrosion protection packages. I haven't seen any silicate free formulas yet, which is required in cars whose timing belt also runs the coolant pump.

As for thermostats, they tend to stick open, rarely stick closed. I've heard rumors of them sticking closed, but I have never seen one or know anyone who has personally seen one stick closed. I'm sure someone will post here that has, now that I've made that statement.

coltarms · Post by **coltarms** » Fri Dec 01, 2006 6:21 pm

As for thermostats, they tend to stick open, rarely stick closed. I've heard rumors of them sticking closed, but I have never seen one or know anyone who has personally seen one stick closed. I'm sure someone will post here that has, now that I've made that statement.

ALLOW ME!!!

I had an 85 accord that had the tstat stick closed. Caused the headgasket to blow, burnt holes in a couple of valves, bent a couple others. Lucky I didn't warp the alum. head..........

keith · Post by **keith** » Fri Dec 01, 2006 6:42 pm

Well your the first. In the past its always been "I know a guy who knows a guy" kind of thing, never first hand. Next question, was it a Honda tstat or an aftermarket? Seems like some Japanese OEM tstats had a eutectic metal that would melt above a certain temperature to prevent this from happening.

Typrus · Post by **Typrus** » Sat Dec 02, 2006 12:29 am

Saw a few examples out of old V-8's we had sitting around our school. A few more exmaples of stuck open though.

Mac · Post by **Mac** » Sat Dec 02, 2006 2:56 am

they can fail closed, my tercel did that when it was put back on the road after 7 years in storage. didn't make it overheat, the engine just ran hot all the time untill i replaced it with an aftermarket t-stat.

several years later, i decided to change it with an OEM t-stat, the car warms up faster, and the coolant temp is more consistant. what am i getting at? use an OEM t-stat for best results.

anyways, your problem is most likeley the "fail safe" T-stat you have in your terc has failed in the open position and needs replaced. your rad cap, if its origional, should probably be changed too. make sure you replace the gasket, and if your DIY make sure you remove the housing from the lower radiator hose for installation, the first time i changed it i left the hose on and ended up installing the t-stat so that it wasn't sitting in the ridge like its suppost to and a week later it pissed out all the coolant.

keith · Post by **keith** » Sat Dec 02, 2006 9:37 am

I can see that with a thermostat that had been good when it went into storage. ColtArms, was you Honda coming out of a period of non use too?

Mac, you make an excellent point about the radiator cap. I have see more than a few people spend a lot of money to correct an overheating problem only to have it fixed with a new radiator cap. New radiators do not come with a new cap either.

I'm constantly amazed at people who always go for the most difficult solution to the simplest problems. I have even seen (at another web site) where people jump in and change a head gasket the first time the temp gauge goes past the mid point on the gauge. There are posters there who always recommend that solution whenever someone asks for advice about an overheating problem. When that doesn't work, then its a new radiator, then water pump and finally the thermostat, never the radiator cap.

In fact, with our Tercel, which my dad bought new and my sister bought from my mother after he passed away, she had a double core radiator installed when the temp gauge would start to rise when going uphill. I think she even had a new water pump put in when that didn't work. When she gave it to my son, I put a new cap on it and that solved the problem. I replaced the thermostat a year later because it stuck open.

xirdneh · Post by **xirdneh** » Sat Dec 02, 2006 4:49 pm

"I'm constantly amazed at people who always go for the most difficult solution to the simplest problems. "

hey, i'm one of those people.
even though i'm aware of it i still tend to go for the most difficult solution.
i think i need therapy?

i have dealt with a stuck (closed) thermostat on my truck (ford f-150).
and once on a tercel (closed).
never had stuck open one.

coltarms · Post by **coltarms** » Sat Dec 02, 2006 6:33 pm

I can see that with a thermostat that had been good when it went into storage. ColtArms, was you Honda coming out of a period of non use too?

No, I had been driving it regularly. That was when I was a teen in Northern NH, and it tended to get pretty cold there..... The car had about 180k on it and it's previous owner neglected most of the maintenance. That was the 1st clutch I ever replaced

I sure do miss that car.....lots of memories....especially in the back seat....

Typrus · Post by **Typrus** » Sun Dec 03, 2006 12:04 pm

My Terc is something of a mystery when it comes to overheating.
I don't suspect a head gasket. Once my compression guage read right, it had good, consistant compression. Low, but consistant. Leakdown tests indicate its all fine.
Yet with heater on full and 7 degrees F out, it rise aboce half. My cap has good spring and is only a year old.

After I replaced a stuck open (Fail-Safe style) termostat in the 86 because it'd start to warm up after 7 miles, not the 4 minutes it does right now (4 to see a change in temp, not to reach operating... Thats about 7). The temp came up to operating pretty quick, but it'd bounce up fairly easily. Hills. Heh. I found revving would drop it. I was worried about my water pump at first, then I asked my dad. He told me to go buy a cap and see what happened. $4 later it was stable. Yay.

After it started running hot in the summer, I swapped for the double-core OEM-style I had from the 84's engine. It ran cooler, but was still a bit warm. Wasn't too worried about it.

Now she will start to get hot if I run lower RPM, say 45MPH in 5th, then I downshift and the temp drops. Now I really am worried about the water pump. I have a spare in the garage, but I don't want to have to do it. I was saving that for my rebuild..... But its not a hard fix thankfully, nor is the pump expensive. And most parts places have it on hand around here. I think I paid $31 or somehting like that. A little more than a fuel pump (which is also on hand easily at NAPA stores).

If I had the money, I'd want to try that electric pump on my rebuild....

Man... Recirculating block heater, electric water pump, MSD Digi-6A ignition, headers, Mikuni 44mm 2bbl sidedraft (or a Weber 38/38 for tunability), 5-angle port and polish, high-volume oil pump, race-style bearings, decked head, dual-rate valve springs, custom cam (haven't decided who or what yet) if I can find them then roller-bearing rockers.
Maybe a custom aluminum 2 or 3-core rad... or just a really wide 1-core with custom slim A/C condensor... Oil-cooling, probably courtesy of Perma-Cool.... Bypass oil filtration, Schaeffer oil, probably Supreme 7000....

Man... A guy can dream.... What do you think that setup would be good for? Buck-50?