'95: Could a rotted heater core cause a low temp guage?

kimcrwbr1 · May 21, 2014

To test the guage pull the 1 wire connector sending unit wire and jumper it to ground with the key on the guage should read hot.

bbb0777 · Nov 18, 2014

Add to this, for people who get here via Google.

Post-fan-clutch change, things better yeah. Gauge is still wonky. I was thinking everything was fine sans the guage, but then - I bought a bluetooth ODB2 reader. The engine if warming up from idle never goes about 181 (kinda weird on a 192 thermostat), and when driving - never goes about 193. All a little low, I've been told.

When letting the car warm up at idle, I notice the upper radiator hose gets warm with the engine, instead of staying cold until the thermostat opens. Also noticed, with the radiator cap off, there's never a sudden movement in the coolant. Probably because it never gets warm enough for the thermostat to actually open.

Taking the thermostat housing out, I see that if I put water in one end of it, it dribbles out the thermostat on the other end. So...it seems like coolant is getting past the thermostat prior to it opening. Put in a new thermostat (Napa Premium this time) - same thing. I almost want to say there's something wrong with the housing...but I don't know. Will update if any more info.

Mark_88 · Nov 18, 2014

Have you checked the temperature rating of the coolant? If the coolant mixture is too weak (as in too much coolant to water ratio) then the coolant will not heat up as high as a properly mixed batch...ask me how I know...

Get one of those coolant testers and check what it is rated for...if way above or below the recommended levels then draw some out and put in some of that water that is meant to be used (can't think of the name right now) in rads and batteries...non-iodized or whatever they call it...that will thin out the coolant and give you more heat...

tomw · Nov 18, 2014

The thermostat will have a small opening to allow air to exit the block when filling the cooling system. The thermostat should seal pretty tight to the housing with a rubbery gasket. The 'ears' should hold the stat from side to side, and keep it in its place in the housing.
Both of the hoses leading to the heater core should be too hot to hold onto when the engine is at operating temperature. The radiator return hose from the thermostat housing to the tank should also be too hot to hold onto with the engine warmed up.
You can install a flushing tee into the heater core hose, and connect to a garden hose to backflush the whole system. A clogged heater core will not get unclogged in most cases by any flush. You can determine the IN and OUT of the heater core by following the hoses to their origin. The feed hose will come from the cylinder head or thermostat housing 'behind' the thermostat. The lower hose into the water pump is the return from the radiator, and may have a return for the heater core coolant.
The sending unit for the gauge might have gotten damaged by the engine overheating and be sending incorrect readings to the gauge.
to

bbb0777 · Nov 25, 2014

OK, solved...ish. The fan clutch was bad - and that improved things. But it wasn't 100%, as it was still *barely* getting above the bottom line on the temperature gauge.

And it turned out: The engine simply wasn't getting that hot.

Why? Coolant was getting around the thermostat, so it was like having a slightly open thermostat open all the time. Tried several thermostats, they (including Motocraft) all sealed about as well.

To corect this, I first tried sealing the thermostat in the thermostat housing better, using water pump gasket making stuff. Using my Bluetooth ODB2 reader / Torque app, I could see my coolant temperature was range while driving was about 15 degrees higher, and the temperature needle was also showing somewhat higher.

Second, for testing, I blocked off about 90% of my radiator (10% being a hole in the middle cut out, roughly in front of where the fan clutch is). I blocked it off with black foam board from WalMart, attached directly to the radiator with two zip ties. Driving - temperature via bluetooth ODB2 reader got all the way up to 231 eventually, and the temperature needle actually went above the middle of the gauge.

So - it was not the heater core, temperature sending unit, gauge, or water pump impellers. The coolant just wasn't getting very hot.

Cut out a larger hole - tested. Cut out a slightly larger hole - tested. In the last test, I drove around for about 45 minutes on a cool night, and the engine temp that varied between 191-201. Seems like a good place to leave things for now. In all of this - the temperature gauge behaved perfectly.

For the last step, I have a Four Seasons thermostat housing on the way. Perhaps being new and smooth it will make a better seal with a thermostat. Or maybe it'll just be slightly better than the Motocraft original. If it does - great, that'll go in the car, and some or all of the foam board will come off. If it doesn't - at least I know, and it'll go on Ebay.

tomw · Nov 26, 2014

You might have gotten the wrong thermostat for your application. I got a Stant from amazon, delivered, for less than local. The local could have been a "freds thermostat & pie" version, so I got the Stant. There was, as remembered, a square cut O-ring around the 'front' of the stat(away from the engine) that fit snugly into the housing. As noted before, there were metal ears that needed a bit of tweaking to make them hold the stat squarely in place in the housing before assembly, and to hold after, I suppose.
Either you lack a good seal, or your stat is not as functional as desired. The stat is still leaking coolant past its obstruction as it is getting to the radiator to be chilled (if not, blocking air flow over radiator fins would make no difference). Fix the seal with a new housing or a good stat. I had to replace my housing as I punctured it with a screwdriver(!!! thought it a casting!!!) and got a stamped replacement. Had to be ordered by Advance, normally not stocked. The Stant sealed well.
tom

Mark_88 · Nov 26, 2014

Good to hear you are on the way to a solution...

Where I live, I've had to block the rad a few times over the years even though all parts were fairly new and functioning...it was just -25 to -35 some times and the little heater just wasn't able to keep the cab warm enough (OK...there were some issues with insulation in the doors and a few other places)...it was dang cold driving for over an hour home some nights...blocking the rad off a bit helped raise the heat levels...

bbb0777 · Nov 26, 2014

tomw said:
You might have gotten the wrong thermostat for your application. I got a Stant from amazon, delivered, for less than local. The local could have been a "freds thermostat & pie" version, so I got the Stant. There was, as remembered, a square cut O-ring around the 'front' of the stat(away from the engine) that fit snugly into the housing. As noted before, there were metal ears that needed a bit of tweaking to make them hold the stat squarely in place in the housing before assembly, and to hold after, I suppose.
Either you lack a good seal, or your stat is not as functional as desired. The stat is still leaking coolant past its obstruction as it is getting to the radiator to be chilled (if not, blocking air flow over radiator fins would make no difference). Fix the seal with a new housing or a good stat. I had to replace my housing as I punctured it with a screwdriver(!!! thought it a casting!!!) and got a stamped replacement. Had to be ordered by Advance, normally not stocked. The Stant sealed well.
tom

Oh, I forgot I hadn't posted all this info in this thread: Yes - I lack a good seal. Coolant is definitely still leaking around the thermostat, just much less.

Prior to the gasket-making - I eventually took the thermostat housing out - and did a "sink test" - tested it via pouring water into it the sink, and seeing how quickly water drained past two different thermostats. Both a "Napa Premium" and a Motorad had water leak past at the exact same rate. Using gasket making stuff, I was able to cut the flow down to about 1/7 of what it was before. Still not perfect, but it's gotten the above results.

So I've got the Motorad thermostat from O'Reillys, a "Napa Premium" from Napa - both of which behave identically in the engine, and in the "sink test". Then way in the beginning...the original Motocraft thermostat, with which it ran cold. Then, a replacement Motocraft from the dealership - same engine performance. So I'm pretty certain it's not a thermostat issue...so then:

Yup, as I said, new thermostat housing on the way, which I'll test in the sink with two different thermostats, and see if it's going to be any better (kinda assume it will be...).

XLTsplash · Nov 27, 2014

If you fill your cooling system with 100% antifreeze, without water mixed in your engine should run warmer.

bbb0777 · Nov 27, 2014

XLTsplash said:
If you fill your cooling system with 100% antifreeze, without water mixed in your engine should run warmer.

Right, that makes sense. I had never thought about that, thanks.

Mark_88 · Nov 27, 2014

XLTsplash said:
If you fill your cooling system with 100% antifreeze, without water mixed in your engine should run warmer.

Hmmmm....I always thought it would run colder...the mix itself is less likely to heat up more (my logic, not fact) and the water thins it out allows it to heat up more...since the water doesn't have anything special about it to prevent heating or cooling too much, I'd always thought the "anti-freeze" was designed to prevent too much heat or too much cold...

now I'm going to have to go look it up... :icon_confused:

Ah ha! I knew it...I was WRONG again... :yahoo:

I am now, officially, 8 for 10 (wrong)...working on that 100% wrong...somebody has to do it...

XLTsplash · Nov 29, 2014

Water cools better than anti-freeze. Anti-freeze offers corrosion and freeze protection.

'95: Could a rotted heater core cause a low temp guage?

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