Overcooling? YEP! overcooling

after an engine change (“new” rebuild top+bottom) my car is running quite cool, 160 deg f, stat is 192. I have installed multiple stats, tested them in hot water, i have an after mkt temp gauge. Both the stock gauge and a/m gauge follow each other. the engine will reach temp if idleing but as soon as i start moving she goes right down to 160 or less. I have 100% radiator coverage of the radiator, no real air flow. when idleing i can watch gauges and at 190-195 stat opens and temp drops. fan kicks in at 210 exactly on time.
anyone have any ideas?..what problems can occur due to running cool? besides lack of heat, and lower mpg.

You probably have a defective thermostat that either does not fit tight and allows bypass of water or it stays open too long. That would be your first and inexpensive fix. There is another thread about an owner whose car will not get over 190F.

“when idleing i can watch gauges and at 190-195 stat opens and temp drops. fan kicks in at 210 exactly on time.” Isn’t there something wrong with this statement??

If this isn’t a mysterious hand-made multi-cylinder beast that you’ve created in your garage, chances are there’s a year, make and model associated with both the car and engine. Try hitting a dealer, and getting an OEM stat, just to be safe. Nothing in your description points to anything other than a badly made or malfunctioning stat.


yes there is Elly, it should have read, “temp drops, right down to 160 deg f or less.” and it will only come over 160 while idling. while driving at any speed (5 to 75) it is 160. I’ve been through 9 stats, 88 deg c, 92 deg c, 195 deg f, as stamped in, also different styles, ie w + w/o rubber gasket. further to get 160, i have 100% radiator coverage.
Docnick, 190 is ONLY at idle. 160 deg f rolling. WITH radiator covered tight to core with hy-temp nylon sheet.
basicly, Chase, it is 95 geo metro, “quit laughing”, 3 cyl, 5 spd, i changed the front steering “knuckle” back to the pre 95, so i can run 12 in rims. and cheaper brake parts.
I looked into a dealer stat, at $ 32.90 !!! it must be gold plated.
All stats were tested by submersing in a pan of cool water then warmed while watching a meat thermometer.
all stats were closed when installed, yes, spring toward head.
I also have a 93 3/5, comes to temp190 and even in sub zero temps stays 185-190. with zero rad cover.
heater air temp = from 93 110 deg f. from 95 = 88 deg f…as would be expected.

What you have to know about the stat is not whether or not it opens when it should. You can tell that from the car’s temp behavior. You need to know about it closing when it should, and about whether or not it is sealing up to the head when it is mounted. Its either sticking open or allowing flow through in some other way.

thanks everyone for help and insights, sorry for shortfalls.
on both gauges, stock + a/m, i can, at idle, watch the needle get to ± 190, (stat opens) and down to 160. then back up 190, open, 160,190,160,190,160.

Hey roller, can you be more specific, now that that I have filled in some holes? Do you have any idea of possible damage that might be caused, internally? I already know I’ll be riden cold round zero.

If hot water flows into the top radiator hose (feel it) before the engine reaches normal temp (190) then the thermostat isn’t doing its job.

I wasn’t laughing, actually. They’re not bad little cars, for what they are. It’s a 1 liter (1.0) engine, and the car isn’t heavy, so they’re fairly peppy even with that little motor. Quite economical, if the driver doesn’t try to make it a race car - 'cause it can never be. A guy that used to work for me had one - I’ve never worked on one, though.

What Cig’s getting at is the job of the stat is not to keep the engine cool (the rad will do that with no problem), it’s to keep it hot. If your stat isn’t starting to close a few degrees below the listed temp (190), then it’s faulty. Simple as that. It should have a temp range that it’s partially open, some degrees below the listed temp. My guess is it’s about 185, but that’s just my guess. I do believe 160 is too low, and it should be partially closed at 185, maybe fully closed at 180 or 175.

Maybe my numbers aren’t quite right, but you should get the meaning, anyway. I’m sure Cigroller or OK can correct those.

I’m not sure what to be more specific about - chaissos basically said it. If the thermostat sticks open then the car runs too cool. The thermostat that you installed might be designed to operate this way. Or maybe its defective. The thing about aftermarket parts is that they are often designed to meet the specs of a whole lot of different cars. The net gets cast really wide so that that same part can be sold for lots of cars, but that means it doesn’t work exactly like the one the manufacturer designed for the car.

But its also possible that the stat is not seating properly onto the head and coolant is getting by even if it is closed. A lot of cars, for instance, have a couple of seating tabs for the thermostat that fit into slots on the head. If the tabs don’t go in their slots it can basically create a permanent leak past the thermostat. The thermostat will open and close around its design temperature. When its cold, closing it puts the floor on the coolant temp. A leak or a sluggish thermostat will constantly circulate coolant through the radiator & have you running too cool.

ok, the one i took out had a rubber 'gasket" that fit around the flange, the largest diameter. it is a ring with a groove for the stat to fit in. and there is a weep hole, for air, that must be at the top. I do like the thought that after market stats can cover a wide range of applications. i have tried 9 different stats, figure
one must have been an oem. maybe not. at $32.90 thats an expensive experiment. i have to pick up more gaskets, rtv is a hassle, to clean off with this meny swaps, and the cure time, and temp, single digits, heating the garage and its cold contents, not practical. anyway i intend to pull the one out of the 93 and put it into the95. and put a different one in the 93. if the “new” one functions properly in the 93, i’ll leave it. then i can figure the one i put in the 95 from 93, should good also. I will keep everyone posted.
Thanks again.

yesterday the temp was about zero so i got brave. using two pieces of 1 1/2 x 1/4 flat steel 4 in long, and two bolts, i made a radiator hose compresser., by drilling a 3/8 hole at the end of each. This i used to cut off the flow from the stat to the radiator,
i figured with no flow through the top hose the car would over heat quickly, wrong wrong wrong. The temp ran about 165/170, rolling. i let it idle when i went in to the post office. expecting 190 or a boil over when i came out i was ready to quickly remove my ‘custom made hose compression tool’, no only made 180 or so after 10 minutes of idle time, following a 21 mi drive to get there. as soon as i began to drive it went down again. repeat performance for two more stops and 35 more miles.
so in effect i created a simulation of a stuck closed stat, which made minimal change in the operating temp. the heater air was warmer, by a good deal, heatercore acting alone. but even when i shut the fan down, the op temp would only reach ± 180.

It seems apparent that coolant is bypassing the thermostat. It’s just a matter of feeling the hoses to pin point where.

I don’t believe it is the thermostat based on all you have tried and reported. BTW- my Camry has the exact same type of tstat and gasket. Those can be a biotch to get seated properly into the groove of the housing but they do a tremendous job of sealing without the need for any goop whatsoever. Assuming the gasket isn’t ancient, it can be re-used many times over for your experimenting purposes.

The thing that sticks out for me is that the engine reaches op temp when motionless. The tstat is doing the job of regulating temp under those conditions. Start moving and what happens? 1. the water pump is turning much faster than at idle and 2. the convective cooling is amplified many times. First test, what happens sitting motionless at temp when you rev the motor for say 30 seconds to 2k rpms or wherever you feel comfortable holding it for about that amount of time? When the engine was swapped out, did anyone leave out ANY of the shrouding or other trim that orginally came with the car? Air dams, shrouds and such like play a critical role in air flow. Sometimes, their removal results in over heating, sometimes over cooling if the area being protected from cold raw air isn’t anymore… Just some things to think about.

“yesterday the temp was about zero”…

I think I found your problem. When I lived in North Dakota we used to put corrogated cardboard or pieces of blanket in front of our radiators to allow the engines to get to and maintain normal operating temperature. The bottom line is that if the ambient temp is that cold, the average cooling system is going to dissipate heat faster than the average engine can generate it. And the faster you go, the worse the problem is. Zero degree air passing through a radiator at even 30 mph can remove a whole lot of heat really fast. More than your engine can create.

Small engined cars with in very cold weather have a problem, epecially in slow driving mode. If you turn the heater on high to keep warm, you may be draining all the engine heat that way.

When I lived in the North we had custom fitted, padded leatherette radiator covers with small flaps that could be opened for highway driving. In the city these covers stayed closed all winter.

Custom fitted, padded leatherette covers? My INTERIOR wasn’t even that classy!

Mountainbike; I lived near a shop that customized these. My 1976 Ford Granada had such a cover with 2 little flaps that you could open and secure with snap buttons. My 1988 Caprice, likewise had one, it cost about $40 for a cutom fit.

I’m sure in Alaska there are shops that sell these covers.

Well, I grew up in an area that routinely saw -25f for a week straight during winter. We never used any radiator blockage devices or block heaters and the only well maintained cars without blasting heat were beetles. :wink: Granted, it took time to get there but the heat was more than comfortable. Nothing like a rock solid car seat and a very very slow turning engine to start out your day. Cars today are designed to run hotter and get there faster.

One other thought, running a 50/50 coolant mix? Too much AF will also make it run cool.