Engine and Transmission Tech

This is a piggy back to my Thermostat inquiry a couple days ago. My car (3.9L --- 160* thermostat---mgb radiator) for years has run low coolant temperature during the fall and winter months. During spring and summer months the car runs betwen 160-180 with occasional blips to 190 in heavy traffic. For me this is a very satisfactory set up. BUT, when the outside ambient temperatures begin to dip below 55*, my car typically runs between 140 --- 120. My heater in January is the equivalent of 5 hamsters blowing through a straw. Not good!
I changed the thermostat yesterday thinking that perhaps it was faulty and sticking open. The new 160 thermostat has the same problem as the one I took out. I can't help thinking that the bypass line from the water pump to the thermostat housing must have some influence on this problem. Does anyone have any thoughts about this? I guess I could go to 180 or 195 to see if that helps the problem, but I'm sure that would create much higher coolant temps in the summer months. Mark at D&D recommends staying with the 160* thermostat. Any thoughts would be appreciated!



Edited 1 time(s). Last edit at 11/01/2011 10:43AM by RMO 699F.

For the same cooling phonomenon, our mutual friend Pete Smith adds a piece of cardboard in front of his rad......either that or add more hamsters.

Mike, after I re-did my fan & radiator on my MG this spring, I also installed a 180 degree thermostat.
When we did the rally to Reno (7500 miles), Temp stayed at 195 deg. (thats where my fan is set to come on) but did move up to around 205 deg thru Mojave Desert (think too HOT for humans) but car ran fine.
Yesterday morning I had MG out and the outside temperature was around 34 deg. and temp gage on MG read around 185 and the heater was WORKING quite well.
Merv

"I guess I could go to 180 or 195 to see if that helps the problem, but I'm sure that would create much higher coolant temps in the summer months."

Not necessarily. If your cooling system is working that well, I think you'll be fine in the Summer. I'd try the 180 year round. Actually, that's what I do on my mine. Can't agree with Mark, 160 is not warm enough for the engine, IMO.

Did the cardboard trick one winter, many years ago on my Ford Courier pickup. Later, discovered the thermostat had come apart.

Honestly I don't know why they still sell the 160* thermostats. The big problem people had with those was that they caused increased engine wear and accumulation of crud in the valve covers. The engines never got warm enough to evaporate the water and acids that accumulated from blowby out of the oil. As for the cooling, the 180 thermostat should be fully open by 190 so from there on up there should be no difference in performance. 210 is not excessively high as long as you don't get into thermal runaway. And if you do, I'd look for something other than an issue with the thermostat.

JB

Mike, your engine should run at the thermostat setting, not any cooler. An aluminum block and heads will have some degree of "air cooling" that a cast iron block and heads don't, but not that much I suspect.
The bypass line is just that a bypass for the coolant when the thermostat is closed to allow it to recirculate in the engine. Shouldn't affect the engine running temp at all. I'd try a 180 degree thermostat and look at improvements to you heater if you want more output there this winter. The conversion to a GM 3 speed blower really helps as the fan is larger and pushes a lot more air than the five hampsters you now have.

A couple of possibilities come to mind Mike.
The first is a poor quality Tstat. A lot of the cheaper ones will leak enough coolant by to cool the engine right off in the colder months. It doesn't take a lot of coolant flow to keep the Rover engine cool. A quality Tstat will close completely. You shouldn't even be able to blow air through it.
The second is the old standby "drilling a vent hole" in the Tstat. Not needed, and it will pass enough coolant to make the Rover engine run cold.
Where is your temp sensor mounted? Is it reading properly? An infrared temp gun is pretty handy to check out the real temp of your motor.
Hope thats helpful
Cheers
Fred

Mike, I wonder if the low winter temps aren't the just the nature of these old V8s. I had the same problem with my 215 whether I ran a 160 or 180, and now the same is true of the fuel injected 3.9, The thermostat in the 3.9 is a 90C from Atlantic British and on 50 degree day like today at highway speeds it will run between 170 and 180 on the gauge. Now that I have added a engine driven fan even at idle it rarely goes above 200 even on a hot day.

My parts hauler is a '98 Dodge Dakota with a 318 V8 with a 195 thermostat and it acts the same way to winter weather. Our Jetta, with a more modern 2 liter engine, warms up to 190 and never moves, winter or summer.

Al

If your themostst is working correctly it will close down in cold weather to keep the engine at proper temp. We tried the BYPASS hole at 1/8 inch and it was too much for a 350 chevy here in AZ. Just a steam/ air bubble hole of 1/16 is all that is needed. I'm still not convinced we need it at all. A goog quality Robert Shaw thermostat at 180 deg and a Fan switch that comes on at 195 and off at 185 off works perfect here in Tucson with the a/c on as long as you have a good radiator and electric fan. In cold weather it should hold it at 180 no problem.
Painless wiring switch #30110
EMP/Stewart components thermostst #EMP308
Available from Summit Racing

I have the same problem. I am convinced it's because of the thermostat housing to water pump bypass hose. It needs to be much smaller or closed off in the colder weather.

The thermostat bypass hose is supposed to allow the water to circulate around the engine block when the thermostat is closed. It is not designed to allow water to go back to the radiator. The routing is from under the thermostat to the pump inlet and back to the block. The purpose is to lessen the chance of cavitation in the pump which can ruin the pump vanes and housing over time. This should not effect warmup time.

Jim

I understand it is to prevent cavitation & that the water is supposed to bypass the radiator & recirculate thru the block only. What I don't understand is why my engine will not warm up & maintain the same temp year round. Some of that water must be going thru the radiator.

I have a new 180 'stat with no bypass hole. The old 'stat works great on the stove. I thought sure it was stuck open (it wasn't). I have the radiator 2/3 cover with cardboard to get it to run at the same temp as during warmer weather. Gee, I thought that is the thermostat's job.

Steve in AZ,

SBC has a bypass built in to the water pump (unlike BBC), so, yes, you would only need a very small hole in the thermostat.

Very odd Carl, but your engine seems to run unusually cool. Maybe the output from the heater core is cooling it enough for winter? Just curious, how's your gas mileage?

Do you have one of those HF infra-red pistols? Be a good idea to check the radiator temps and gradients to get a better idea of what's going on. Same at the hoses and thermostat housing.

Jim

Nope. Don't really trust the Harbor Freight ones. BTW, their Cen-Tech #69465 sale price of $35.99 (compare at $69.99) and "special" price from the email flyer $19.99 plus sales tax & a trip to the store can be had on Ebay for the same $19.99 with NO sales tax & free shipping. So, I don't trust their sales promos, either.

[www.ebay.com]

Gas mileage to Durham was better than 27mpg. Temp gauge runs right where it is supposed to be in warm weather. Didn't try shutting off the heater valve cause I wanted some heat in the cabin.

Gonna go remove my engine fan & just run the factory twin electrics until the weather gets warm again.

Hey Carl,

The bypass hose on the Rover engine goes from the coolant outlet on the head to the waterpump inlet.
It has no access to the radiator at all. In fact it causes more problems in the summer with overheating as it always bypasses some of the rad cooling.
It's a bit of a double edged sword. Without the by pass the coolant would stagnate in the block and the thermostat would never see the actual water temp. Causing the engine to overheat.
With it you reduce the rads effectiveness when it's needed most.
That's why modern designs use a dual acting tstat to block the bypass under high demand.
The only access that the coolant has to the radiator is through the thermostat. So if your rad is warm and your engine isn't then there is only one answer.
Most likely you have the wrong thermostat. Not by your doing, but due to the aftermarket,
The thermostat just happens to be the same size as a small block chevy. So that's what they sell you. They work fine on a big cast iron engine but leak too much for the little aluminum motor. Many of the SBC tstats even have a small "V" notch in the disc to promote self bleeding and to allow the tstat to sense water temp as they don't use a bypass..
This notch is enough to cool your engine right down. Let alone the crummy build quality of most these days.
The proper tstat will have a tapered seal. The best ones have a rubber seal.
You should not be able to blow any air through them when they are closed.
So if reducing the efficiency of your rad fixes the problem it has to be the tstat.

Cheers
Fred

I think Fred's probably nailed it.

But I also think, knowing your car, that your engine is remarkably well optimized and operating at an efficiency that many of us only dream of achieving. Which partially explains it running cooler. So maybe you have less heat to spare.

Jim

Have you tried covering the oil pan?

Oil carries a fair amount of heat away, especially in an aluminum engine.

I've seen other engine swaps do the same thing in winter and covering the pan helped some of them.

Just for a test, some cardboard, tie wire, duct tape, whatever, as long as it stays put.

Of course, make sure it doesn't touch the exhaust, external combustion is bad. ;)

Just clarify, I have a Buick 215. The Rover diagram above is the only one I could find. Looks similar, except my bypass is a straight hose from the intake to the back of the timing cover. The port sticking up off the water pump goes to the upper heater core fitting.

Fred is right about the thermostat being SBC cause that is what I bought both times. I thought they were interchangeable. Not sure they aren't for Buick/Chevy. the two I have do both close all the way.

I removed my engine driven fan (still have the OEM twin electrics). Greatly helped warmup. :) Can't tell much else for now since we are having an extended Indian Summer with temps in the high 60s to low 70s.

Maybe I just have less horsepower making less heat. :)

Carl, I'd get a thermostat for specifically a 215. Second choice TR8 or 3.5 Rover if they interchange.