Hello everyone. First time posting on here. I have an issue with my freshly rebuilt 235. After idling for about 10-15 min the temperature gauge is pegged. The top of the rad is hot but the bottom of the rad is cold. I suspect the water pump is not pumping. Any advice? The pump is brand new. I can't recall where I bought it. Is there possibly a look-alike water pump that id designed for opposite rotation? Im stumped and Im new to these engines. This truck has only been drive around the block once. Other things to note: Just installed the heater today. Heater core hoses both get hot and heater blows hot. Its almost like the water pump is circulating the Thermostat is a 180. I believe installed correctly (coil spring down) Rad is not overfilled Rad cap is 1.3 bar Rad is new rad hoses get pressurized with cap on Ran truck with rad cap off. still pegs the gauge with rad cap off I can squeeze the hoses and get the coolant to rise After turning off and letting sit for 10 min, temperature probe in coolant at top of rad read 180F. - so not screaming hot... I took the belt off to experiment spinning the pump. Spins fine. Should I be able to hear any sloshing around? I suspected an air lock but not sure how to check currently I have the coolant drained and water pump and thermostat were removed to inspect. Everything seems fine to me.
Do you have an infrared temp gun that you can use to measure the actual temperature of the head, etc? That's the place to start...see what the gauge really means when it's pegged.
Like Jim said, measure actual temps. Heater working means water pump is working. Not pushing water out the rad with the cap off (and gauge pegged) tells us the engine is not as hot as the gauge is saying it is. Good chance it's only a gauge problem.
If it is pumping coolant through the heater core the pump is working. If you can run the engine with the cap off, and the temp gauge is pegged and it isn't puking coolant out the fill neck the main problem is the gauge. Especially if you have an electric gauge. Unless you work it hard an engine with a good cooling system and a 180 thermostat should run about 183/185 degrees. My guess is that the temp in Pa is down in the low 30's or below, the thermostat is working good and the heater core is big enough that is is serving as the primary radiator if it is putting plenty of hot air out and heating the car nicely. To the point that the thermostat never actually fully opens and isn't letting a lot of hot coolant go to the radiator. That happens when it gets down cold and is pretty normal. Back in 1978 my Best friend was running a 29 Model A roadster with a small block chev and a Walker Radiator. His gauge was showing 269 degrees but he walked around in front of the car with it running to show the Walker rep at the show that it was hot, No shirt on and he opened the radiator cap and not one whisp of steam came out, I saw my Snap-On tool guy at the show and asked him if he had a radiator temp probe on the truck and he did and sold it to the Walker rep who tested Ron's radiator that was happily working just fine at just over the rating of the thermostat. It was the name brand gauge that was off. Meaning that even though the frigging gauge is pegged, if you can remove the radiator cap or run the engine with no cap on the radiator that engine is NOT HOT!
Since you're running a 235, I found leaving the temp sender out at the rear of the head while adding water worked. Once the coolant started to run out, I placed the sender back in. I only had to burp the system once and had water at the right level.
I was suspecting gauge too. Thanks for the quick replies, guys. The gauge is original and was broken (thin little coil wires off their posts). I repaired with solder. Good call on the infrared gun. I wish I made this post before tearing everything apart. Ill pick up a temp gun this week (along with new gaskets), put it all back together and let you know.
It has to be the gauge or the wire to the gauge is grounding out. My 235 has never, ever been near 180.
Take the thermostat out and see if it circulates better. Then put the thermostat in a pan of water with a thermometer in it and see at what temperature it opens at. That will tell you if the thermostat is defective.
Shouldn't the bottom of the radiator be cold? I mean that's the radiators job. And if only after 10 minutes, the therostat is just opening.
Pull the thermostat and run it. I had a defective new one just a few days ago from Napa for a 4.3 gm v6 It happens now and then
In the past I have had occasional issues like this. I now remove the thermostat and fill the radiator until I just see the coolant coming into the housing. Then put everything back together and run the engine. Takes care of any air lock in the system
Sounds exactly like the "air lock" problem I had with my 235 the first time I ran it. It overheated and blew the lower radiator hose off. It turns out it was air-locked when I filled it with radiator fluid/water. I drilled a small 1/16 hole in the thermostat to prevent this from happening in the future if I ever drained & replaced the fluid. I read online about where others had done this.
you can disconnect the heater hose from the lower thermostat housing to get rid of air lock, but if the heater is working, then it sounds like it's probably full of coolant.
Those temp gauges have a fluid inside the tube. If broken the fluid sprays out like it’s under pressure. Don’t think you can just solder them.
GENTs, a for once in your freaking lives read his post all the way through before posting your wild ass guesses. True, with the cap off he should be able to see coolant move in the top of the radiator as soon as the thermostat opens. Not a bad idea to pop the hoses off if he hasn't and see if a plastic cap got left on, Thinking that I have those on my new radiator out in the garage. I'd shut the heater valve off and see what happens, it may be that the heater is keeping the engine cool enough that the thermostat isn't opening up very much if at all. This especially when most of the country is cold as all get out right now.
Is there a fan pulling air through the radiator while its sitting and idling? Not that it is the current issue, but I didn't see it recorded. If the gauge has a copper tube to the temp gauge that was been broken, the gauge can not be reading correctly unless it has been refilled with the gas, resealed, and calibrated, soldering it closed won't help. If it has wires to the gauge and you soldered those, you may have damaged the gauge. If the cap is off the radiator and the gauge is pegged, the gauge is bad, because an air pocket at the sending unit would show low coolant temp, not a higher temp. It measures coolant temp, not air temp, without coolant, the gauge won't function. You have more things indicating a bad gauge then any other problem.
Bad gauge is my first guess. If it has a bulb and tube sender, it should read cold all the time if it's defective. An electric sender, if it's new is a possibility. If it's old, it's likely. Just because it's a new one does not mean it's good these days. The sender must match the gauge. If it doesn't boil and puke, it's not over heating. If it needs soldering, it needs to be replaced. Get one from somebody other than NAPA.
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