Overheating issue - I am stumped!

[Mattchu60]

I will try to get a picture, but I didnt change anything over the stock setup for the heater hose - disconnected the one from the intake when I removed the engine, hooked it back up with I re-installed. The radiator has a connection point for the coolant to flow into the radiator after it passes through the heater core.

Its like this on mine - leaves the intake near the thermostat, routed into the heater core, leaves heater core and travels to the radiator, leaves radiator and travels to the water pump. This is the stock setup from what I see.

[Dead Parrot]

My 75 is like yours. Output from the intake manifold port, through the heater, return into the radiator. If that is the flow you are talking about happening cold, then things are working as expected. There should be minimal flow from the radiator itself with the engine cold and t-stat installed.

A lot of folks assume the water pump port is an output and run from that, to the heater core, and back to the radiator, then complain of poor heat output during cold weather.

Not sure when or why GM switched from return to radiator to return to water pump.

[Custom.Chevy]

i really wish the heater hoses on the c10 were the same size. im also running a serpentine belt system on a newer block. my heater core is way bad and leaking on my floor. thank god i rhino lined my cab floor! I"m currently in escrow from selling my home and buying another so i have no access to tools or a garage, does anyone know any good tricks to bypass the heater core so i can still drive my truck. its summer anyhow no need for it.

[rich weyand]

This plus a foot of both hose sizes (3/4 and 5/8) and a couple clamps gives you your bypass.
http://www.autozone.com/fittings-and...or/102831_0_0/

[ironroad9c1]

OK first off factory gauges are there for Amusement only , get a real temp gage for that spot in the head, you can even just get a cheap mechanical one and hook it up temporarily and take a drive, , the fan clutch , usually only causes overheating at slow times like in stop and go traffic, the fan clutch is only slightly engaged when the engine is at speed moving down the road, you can check it by revving it up from under the hood watching the fan, you should be able to tell its disengageing at higher rpms and reengaging when you bring it back down to idle, also its hard to get a good quality tstat nowadays being as everything has moved offshore, and last if the intake manifold is showing the correct temp the rest of the engine will be pretty close to that temp. once everything is warmed up. also new engines tend to run a tad warm until everything breaks in.

[rich weyand]

Originally Posted by Dead Parrot

Not sure when or why GM switched from return to radiator to return to water pump.

The engine comes up to temp faster, because all of that extra water, and the heat-radiating effect of the passenger-side radiator reservoir, aren't in the loop. The engine comes up to operational temp faster, and the thermostat opens sooner, reducing the buildup of hot spots in the engine waiting for the thermostat to open.

But the OP doesn't want to do the improved routing apparently.

[Mattchu60]

been a busy day and I haven't had any chance to take pictures yet of my setup, i work two jobs and just got into the house for the day (started at 630 this morning). I'll try to get one tomorrow.

guessing part of the issue with my heat buildup is this being a new engine, its very tight and creating a lot of heat once the T-stat does open, seems to be running around 210-215 on the highway. I have a 180 T-stat coming from Rock Auto which I think may help somewhat, should open it before the temp starts soaring (thats my hope).

[Mattchu60]

Got pictures of the engine bay. Here is one of the top side - you can see the heater hoses exit the intake and dumping into the radiator. I believe this is not routed back to the water pump because the coolant flows over the trans cooler in the radiator.


Heres one of the sensor that keeps going high.



Heres the guage on its way to the high mark during warm up.




Last, picture of the truck. Been using it for pulling tanks around the farm the last week, its dusty and dirty from a lot of gravel travel.

[Dead Parrot]

That 'hose' off the intake looks an awful lot like a re-purposed AC hose instead of a normal heater hose. Wonder if it is restricting flow somewhat. That might explain your temp spiking before the t-stat opens. Without the free flow of water through the heater, it just sits static in the engine until the t-stat opens.

BTW- That truck looks very clean compared to most farm trucks I see.

[Mattchu60]

The heater hose use to come off the rear of the engine, thats why is has that bend in it. Its not kinked and I can see water pouring out of the heater core exit hose into the radiator.

I may replace it anyways though, because it looks sort of dumb the way its setup, rather have it come strait off the intake.

[wilkin250r]

Originally Posted by Dead Parrot

A lot of folks assume the water pump port is an output and run from that, to the heater core, and back to the radiator, then complain of poor heat output during cold weather.

Not sure when or why GM switched from return to radiator to return to water pump.

I believe the manual transmissions had the heater return to the water pump, while the automatic transmissions had the heater return to the radiator. At least, that's the one thing that stuck in my head from a factory hose diagram I saw years ago.

[KQQL IT]

Mine has no heater or hoses, pipe plugs in the holes.
I'd be more concerned with the gauge being accurate and thermostat opening with pressure against it.

[ptc]

Have you physically tested the water temp in the radiator with a "simple thermometer" instead of all these new fangled 'tools' like laptops and infrared and gauges and all? Im an Infrared THermographer and I still verify all my readings with another source ALWAYS.

I know it sounds too simple.... but maybe your water temp is actually just fine like your "Dad' says....

http://www.ebay.com/itm/General-DPT3...25.m3641.l6368

[Katrina/10]

I find this interesting because I put a complete 87 engine with TBI into my 71, and the temp gauge does exactly the same thing as yours! I have had many carbureted V8s over the years, but none of them ever did this. Aftermarket mechanical gauge in the dash reads 230 degrees before the thermostat opens, then goes to 200. I have a 195 thermostat installed, which I did switch out for a new one, with no change. I was considering drilling a hole in it until I read it had no effect on Matt's truck.

I don't like seeing the gauge go up so high either, but I could not think of anything else to do with it. So, I have been driving the truck for two years, and it has not caused any problems. It just puzzles me why this would happen.

[Mattchu60]

I am going to try a 180 Stat over the weekend. I dont know if it will help or not. One of our theories is that the since the heads are iron and the intake is aluminum the intake is cooling a little more than the heads which is causing the stat to open slower.

Doesn't really seem like coolant would drop 20-30 degrees within a few seconds though as it travels from the head to the intake. Starting to think more and more that its just faulty gauge readings. I have another temp sender coming to try as well. Thought about putting a mechanical gauge in the head to see what it reads in the future.

[cadillac_al]

The coolant isn't moving when the the thermostat closed. The coolant in the head is cooking while the intake warms up. It seems perfectly normal to me. My truck gauge doesn't do it because it is the stock gauge for amusement but does settle on a normal range every day like clockwork.. Rich Weyand has be intrigued once again with his theory of "improved routing" of the heater hose. It makes perfect sense but I probable won't change mine either since my trucks and cars seem to warm up within 2 miles anyway. In my experience the heater hose was routed to the radiator in heavy duty applications and big luxury car applications. It may even have better flow through the heater core but never spent much time thinking about it.

[Dead Parrot]

There is some flow through the heater core even if the t-stat is closed. Given where the output to the heater is, it might favor the passenger side head and account for the driver's side head spiking a bit before the t-stat opens.

My truck has an aluminum performer intake and I haven't noticed any temp spiking. Standard sample size of 1 disclaimer.

[Gotenntitans]

Hope it's not a head gasket. That happened to my 97. GTT

[nonstop]

My big block runs hot with a 195 thermostat, but just about right with the 180. With that said, I am still leaning toward a thermostat issue since there is a spike, then it drops and settles.

[Dc42d76]

Have incorrect intake gaskets been ruled out ? 88 and up engines use a reverse rotation water pump driven by the smooth side of the serpentine belt. This set up requires the rear cooling ports in the cylinder heads to be blocked,the 88 and up gasket will come with the block off built in and will be marked rear on the gasket. Looks like your 87 water pump is driven by the ribbed side of the belt so this would be a standard rotation pump, so all 4 cooling ports need to be open for this setup. I have also seen these gaskets installed incorrectly with the rear section of the gasket facing forward blocking off the front cooling ports. Kinda think something like this is going on.

[Mattchu60]

180 stat didn't change anything, just runs cooler after my temp spikes.

I am going to try Rich's idea of an external bypass. Trying to determine how to best rig one up. I'd like to leave the heater core bypass in place and use the hole on the driver side of the intake and run it to the water pump, this way I'd have coolant bypassing on both sides of the motor.

[78trk]

I had a 350 that did the same thing one day going to work. I did everything you did including taking thermostat out. The key was it only happened on start up. Then temp dropped to normal. It was a cracked head. Found it when I took the heads to head shop. I think crack was open and then closed when temp came up.

[rich weyand]

Originally Posted by Mattchu60

180 stat didn't change anything, just runs cooler after my temp spikes.

I am going to try Rich's idea of an external bypass. Trying to determine how to best rig one up. I'd like to leave the heater core bypass in place and use the hole on the driver side of the intake and run it to the water pump, this way I'd have coolant bypassing on both sides of the motor.

That, or try routing the heater hose return to the water pump and get the radiator reservoir out of circuit. The water jacket should heat up faster, before hot spots develop, and open the thermostat.

Both are worth trying. Take the one with the best results. There must be a reason the General changed the heater hose routing.

I'm thinking those heads have no internal bypass, or the gaskets don't accommodate it. Something is going on, because I have none of these issues. The differences in my setup: heater hose routing, and stock heads.

[Desert1957]

I would like to mention something I noticed on the pics just posted.
My 87 has that steel line shown at the rear of the intake manifold / passengers side, Coolant comes out of the intake at the rear port, through the heater core,returns to the water-pump.

maybe should be hooked up like pic below.



Desert

[Mattchu60]

Yes, you are right that it exits from the rear on the original setup. My new intake has the outlet on the front so thats where i had to connect it. Possible that this does have something to do with my issue though.